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Update on the Manish situation

The fact that one of the moderators is pretty much inactive has been brought up many times already (e.g. this meta post from last year). In fact, he has been invited to step aside a couple of times by now, with no feedback from his side (AFAIK). I believe it is important to have a conversation about it at some point, so why not now?

Do we want this person to remain a moderator? Is there any mechanism to enforce the decision if he does not manifest any will to follow the community's wish?

• FWIW, the Stack Exchange administration tracks moderator activity on every site; there are no moderators here who have been completely inactive for an extended length of time. – Shog9 Feb 20 '19 at 3:19
• @Shog9 Thank you for the input. I guess that kind of depends what you mean by completely inactive. Is just logging in/out enough to be considered active? Or you do have to e.g. review flags or something of the like? – AccidentalFourierTransform Feb 20 '19 at 3:49
• When I talk about moderator activity, I'm generally talking about stuff that would contribute to a list such as the one I posted earlier this year. – Shog9 Feb 20 '19 at 3:55
• Last october I saw a question which I answered migrated to chem SE (which he moderates) by him. I don't see how such activities could be noticed by most users, unless there's something of the sort in the mod tools. (I'm not suggesting that one migration means anything significant though) – user191954 Feb 20 '19 at 3:58
• It was my understanding that, while he'd decreased his activity here, he was still quite active as a chem.SE moderator - but it does seem that his participation there has tailed off significantly in late 2014 (which, reminder, is coming up on five years ago) with his phys.SE moderation tailing off in mid 2016. – Emilio Pisanty Feb 20 '19 at 11:16
• He was a great moderator, with a calm and conciliatory voice over many rough conversations, and he was extremely active in improving the site and the platform, both actively writing code (example) and participating on the mother meta. But it does feel to me that if he's not actively moderating then him having a diamond doesn't make much sense. There's a proportionality to moderator powers - we give additional authority to people who will use it because we need them to do so - and if the tools are not being used then they should be put back in their box. – Emilio Pisanty Feb 20 '19 at 11:21
• Is it implausible for the mods/SE team to contact him, maybe via email, and request him to respond to this post, if at all he is in a position to respond? While site users can debate his continuation/dis-continuation as a moderator, with all the service he has done to the community, if he has to step down, he deserves the privilege of being the one to make that decision. – 299792458 Feb 23 '19 at 11:53
• @Chair - Correct. But such an attempt must precede any drastic measure from the SE team, if there is ever going to be one. :) – 299792458 Feb 23 '19 at 14:49
• PLEASE NOTE: His "bio" links to his Twitter account, on which he was active 15 hours back (from the time of posting this comment). Any one with a Twitter account can perhaps reach out to him. Hoping somebody would volunteer. :) – 299792458 Feb 23 '19 at 15:03
• @299792458 If 'drastic measure' means 'removal from the mod team', I'd say that the SE team has already made it clear that they don't remove mods for inactivity, and in this case, we even have a couple of 'invisible-ish' actions of moderation from Manish, including the migration mentioned in my first comment. – user191954 Feb 23 '19 at 15:14
• @Chair - I agree. Thanks. – 299792458 Feb 23 '19 at 15:22
• I would be much more comfortable if Manish just said something. This post has been on "hot meta posts" for over a week now. – knzhou Feb 28 '19 at 16:59
• "In fact, he has been invited to step aside a couple of times by now, with no feedback from his side" I wrote a longer answer clarifying things, but just wanted to note: I basically rarely opened meta, so I never noticed these things :) – Manishearth Mar 3 '19 at 16:43
• @Rishi Actually, SE does remove moderators for inactivity, if they don't perform a single action for a period of six months; at that point, they're emailed, and if there is no response or the mod says they want to resign, their status is procedurally revoked. In this case, he was performing an action at least once every six months, so he didn't fall under that policy; however, the same can apply if 1. the user keeps responding that they want to continue moderating, or 2. the rare case where SE forgets to remove the tools: ... – gparyani May 6 '19 at 23:17
• ...there was one case on the now-closed Startups site where a new mod was appointed to fill in the gap caused by one mod not being seen in the last three years, but that mod's privileges weren't revoked for some reason. – gparyani May 6 '19 at 23:18

Oh, wow, I hadn't realized this was going on :)

I first just wish to apologise to the community, both Chem.SE and Physics.SE, for my lack of activity. I'll shortly explain what happened, but I also just feel bad for causing this conflict, and think I could have handled this better. Sorry about that.

So a bit of background: Around 2014 I started getting involved in the Rust community, and my capacity for dealing with stuff online decreased. I also was just busier in college, and balancing my time on Stack Exchange became increasingly harder. I still spent time moderating, though.

I've always had a bit of conflict in picking between a career in software vs a career in physics -- I really like physics and picked it as a major, but I've really enjoyed programming. My opinion eventually shifted from being set on doing physics to doing software (for a complex tangle of reasons), and I eventually got a job doing Rust stuff at Mozilla.

This also meant that Being Online was a part of my job so I didn't have as much of an inclination to participate here as I used to. It also decentered physics from my life, impacting my participation similarly.

But Stack Exchange used to be a big part of my life. It was an online community I truly enjoyed, and I'd learned so much from it, both in terms of actual physics/etc as well as so many things about community dynamics. A bunch of the stuff I've learned here has been applied to the Rust community at a fundamental level, and it's overall been super helpful. So I couldn't bring myself to stop participating. Instead, I felt like I would eventually have time again, and that would be soon. Sometimes I'd drop by and moderate a couple things and check out the meta and overall be really happy that this place exists and is running smoothly. The comm team sends out these check in emails to semi inactive moderators and that would occasionally spur me into participating a bit again, but it never lasted. I recognized that this wasn't sustainable, but it always felt like "eh, I'll have more time next month".

Of course, tomorrow never comes, and I've only gotten busier over time. I still love this place to pieces, but it's just hard to find time to participate.

Honestly, moderation isn't the ideal way for me to participate anyway, as someone who isn't doing physics all the time anymore I should probably spend more time doing q&a for fun, not moderation. The reason I like moderating is that I really care about communities I care about being pleasant spaces, and I care about it enough to consider it my duty to help. But I'm not helping right now, and if I wanted to I can help quite a bit without having the diamond. There's really no reason for me to still have the diamond, it's just taken this nudge to cause the reflection necessary for me to explicitly realize that :)

So yeah, I definitely should step down. Consider this my resignation letter.

It's been fun!

I hope to eventually have time to participate again. I'll definitely be dropping by now and then.

• thx for your work on the site! for/ under a variety of reasons/ circumstances theres a major exodus of physicists → coders/ developers/ software engrs, there are many cases of this mentioned in Physics Chat many by hi rep users + other mods and hope/ encourage everyone to drop by with their own stories, and its just a great place to try to build up community connections or other informal discussions etc. – vzn Mar 3 '19 at 16:23
• Hey Manishearth, thanks for chiming in :) – David Z Mar 4 '19 at 9:01

I'll post this as an answer since it seems there's disagreements and it's important to get a feeling for folks' responses to this.

For one, I find that a particularly useful tool for gauging moderation activity is the All Actions tab on the Activity profile page, or at least a reasonably zoomed-out view of it. If you look at any given active moderator's All Actions history, you'll see a bunch of reviews, a bunch of edits, and a ton of moderation-related comments, in addition to the standard-user interactions with the site. We can't see all of a moderator's actions, since many of them (like, say, deleting obsolete comments) are designed to be invisible.

However, I would claim that if a moderator hangs out on a site in a moderatorial mood, for a few hours, then they're not going to only do those invisible actions - they're going to end up doing stuff like moving discussions to chat, fixing the tags on a post, approving an edit suggestion, or opening or closing a post here or there, which do leave a visible trace. For Manish, the last such activity dates from May 2017. While I have no trouble believing Shog9's assertion that Manish's moderatorial actions over, say, the past six months, are strictly-speaking nonzero, I am having a hard time swallowing the argument that it crosses any reasonable line drawn above 'negligible'.

And, frankly, it does feel to me that if he's not actively moderating then him having a diamond doesn't make much sense. There's a proportionality to moderator powers: they represent additional authority and powers which we give to some users because we need them to do use it. If the tools are not being used, then they should be put back in their box. There's no hard feelings about this, but I do think the position of moderator should be seen as active, and not just this special status that's conferred on you for life regardless of whether you ever come back to the site or not. I think it's part of an outlook where we do periodically, as a community, take clear looks at our moderation stance and evolve it as necessary. Site culture shifts, and we need all of our moderators along on the ride.

And in particular, I think OP is right to want a clear participation and used-in-practice line of communication with every moderator. We have a substantial amount of turnover, and a bit of digging is likely to turn up a substantial fraction of our active user base who joined after Manish effectively stopped moderating.

It's also worth noting that the stepping-down of a moderator who had become inactive has explicit precedent - mbq was elected as a moderator in 2011, together with David Z and dmckee, and s/he stepped down in mid-2014, about some six months after the last of their publicly-recorded moderation activity. Not to mention stronger precedent on other SE sites.

More importantly, though, to address the key voice that we should be hearing from here: Manish, what's up? What is your take on this? I can very well understand the pressures pointing away from physics and away from internet participation that come from a move to software development. Obviously the 2013-era Business As Usual has been replaced - but by what?

• Just one little thing I'd like to pick on: it seems reasonable to ask that every moderator be generally responsive to communication, but that shouldn't mean that any user is automatically entitled to a discussion with a mod of their choice, just like a user isn't entitled to a discussion with any user of their choice. I don't think that's what you meant but I thought it worth being clear. – David Z Feb 21 '19 at 1:26
• Another important thing I'd like to add: moderators are supposed to be active on meta, and the Quorum/convention badges for meta participation are mentioned on candidate nominations. They have an icon in the top bar to notify them of meta activity. But Manish was last seen on physics meta on the 28th of November. – user191954 Feb 21 '19 at 1:59

Just a quick note about the moderator perspective on this: as far as the duties of moderation are concerned, it doesn't really matter to us. After all, if someone is not regularly acting as a moderator, whether they have a diamond or not doesn't make any difference in our ability to carry out those duties. And if something is causing a problem, we have ways to deal with that; for instance, if we feel there are not enough active moderators to handle the workload, we can coordinate with the SE team to schedule an election.

Is there any mechanism to enforce the decision if he does not manifest any will to follow the community's wish?

Separately from what I said above, individual people in the community (including mods) can have their own opinions about whether it makes sense for a moderator to retain their diamond even if their activity is low. However, as far as I know, there isn't a process to turn those opinions into action, at least not a direct one. Moderators' accountability to the community is less than e.g. a democratic system where elected officials can be impeached, and that's by design, since moderators need the freedom to make unpopular decisions sometimes without worrying about their position being at risk. (At least, that's what I read somewhere. Of course if the mods are constantly at odds with the community, that's a whole different kind of problem.)

If there are serious concerns that would warrant a moderator's removal from the role, there's a process in place by which the SE team, if prompted by "numerous, substantiated complaints from users on the site", can do it, but I don't think the team would consider low activity enough to start that process. (I'm not saying that is or isn't how it should be, I'm just saying that is the current state of things.)

• Something I've seen on at least one other SE site with a similar appearing issue, was that a moderator without much visible activity was apparently still providing valuable advice to the more active mods, about disagreements, meta discussions, site direction, etc, via private chats or other channels; and they valued that mod's input even if they weren't as active as they were in their "prime", so to speak. I'm not sure if you or any of the other mods are interested in speaking to that, one way or the other. I understand that's somewhat private so please don't feel any obligation to respond. – mbrig Feb 21 '19 at 16:57
• Thanks for bringing that up, that's a good point. I would definitely want to check with the rest of the mod team before saying anything about that. – David Z Feb 21 '19 at 19:51
• @DavidZ Any update on that comment? – AccidentalFourierTransform Feb 28 '19 at 22:51
• Not yet. Sorry, I've been busy. I'll look into it. – David Z Mar 1 '19 at 0:15
• @AccidentalFourierTransform I got busy and didn't get to reply over the weekend, sorry. But we came to the conclusion that, in general, if a moderator isn't active on the site, we would be comfortable revealing whether they are interacting behind the scenes in a way that the community at large wouldn't see. – David Z Mar 4 '19 at 9:08

Said moderator logs in from time to time, so we cannot say for sure whether he's actually doing any actual moderation or not. The two options are

• He does not moderate at all, or

• He does perform some actions occasionally, but leaves no trace.

In either case, I'm not too happy about the situation. If this person is not doing any moderation, then the logical course of action is to step aside.

On the other hand, if he really is doing some moderation in the background, I would feel uneasy about the fact that a person I never interacted with is doing such important work. I want to hold moderators accountable for their actions. Manish was elected, spent some time moderating, and eventually became inactive, long before I joined SE. I have no idea how he behaves, and I don't want him to have the power that comes with the responsibility of being a moderator.

In conclusion, both options lead me to suggest that maybe he should resign. I am obviously very thankful for his time making this community what it is today, but I see no point in him staying a moderator when he has de facto resigned a long time ago.

There are many actions that the moderators take that aren't visible to users (e.g., cleaning up comments), so the bulk populous of this site would not able to determine how much said moderator is actually doing.

I think that so long as the moderator is not actively harming the site (no such evidence) and the current (visibly?) active moderators are not complaining (doesn't seem to be the case, given DavidZ's response), there really isn't cause for anyone to try removing the moderator.

An apparent "invisibility" isn't enough to justify trying to remove a moderator, in my opinion. I think actionable evidence is what is needed to move forward, but pretty much all of us are not privy to such evidence, hence any calls need to come from higher up (i.e., other mods or SE team).

• There are indeed many moderator actions that aren't visible to users, but I find it really implausible that any reasonably active moderation activity will leave a completely clean trace on the Activity page. A user who spends a meaningful amount of time handling moderation duties and yet none of the things they saw on the site during that time led them to post even a single (still-extant) comment over a full two years? Is this really something we want to keep on the table as plausible? – Emilio Pisanty Feb 20 '19 at 17:07
• I don't see why that's not plausible, especially given shog's comments to the main post. I also don't see what business it is of ours (i.e., non-mods) to complain about the invisibility of another mod & raise our pitchforks. If the mods or SE team see fit to remove a mod, that's fine. I just don't think we regular users have any business shoving our noses where they don't belong. – Kyle Kanos Feb 20 '19 at 17:29
• Shog's comments only state that the moderation activity is strictly nonzero; it sounds like one deleted comment every six months would snooze that alarm. But the concept of a moderator who, say, has a go at the moderation queues once a month for an hour or so, and yet never once approves an edit suggestion, or reopens a post, or cleans up a tag, or indeed interacts with any post in any visible way, over a full two years? If this is really being considered as realistic then to be frank I think that conversation's gone completely bonkers - or at the very least it does call for an explanation. – Emilio Pisanty Feb 20 '19 at 17:42
• And I don't see why this needs to be viewed with a "raising our pitchforks" lens at all. OP has a good point that moderators are community representatives and that there is now a significant fraction of the userbase that's never had any chance to interact with a specific moderator, and they are right to want that chance. – Emilio Pisanty Feb 20 '19 at 17:47
• I simply disagree. If any mod chooses to do $\epsilon>0$ amount of work, great & there really isn't anything to complain about. If they choose to do $\epsilon=0$ work, sure someone should say something. But it shouldn't be us. It should be the people impacted: other mods and SE team. – Kyle Kanos Feb 20 '19 at 17:53
• Re: "actionable evidence", are you talking about evidence of a mod doing harm to the site, or just evidence that they're not actively moderating? If the former, note that the rest of the mod team (and SE) is watching for that sort of thing and we would definitely do something about it if we saw it. In the latter case, you make a good point that only mods/SE have access to the evidence about how much a given mod is actually doing, and that may carry some responsibility to represent the community's view on it, even though we (mods) may not care about it ourselves. – David Z Feb 20 '19 at 21:33
• @DavidZ I would say either/or: either evidence of harm or evidence of negligence. It seems some/many feel there is enough of the latter to push this this far, but I don't feel it's compelling evidence given how much is hidden from our view (by design!). – Kyle Kanos Feb 20 '19 at 21:36


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# Geometric Thickness of Complete Graphs

Dillencourt, Michael B. and Eppstein, David and Hirschberg, Daniel S. (1998) Geometric Thickness of Complete Graphs. In: Graph Drawing 6th International Symposium, GD’ 98, August 13-15, 1998 , pp. 102-110(Official URL: http://dx.doi.org/10.1007/3-540-37623-2_8).

Full text not available from this repository.

## Abstract

We define the geometric thickness of a graph to be the smallest number of layers such that we can draw the graph in the plane with straight-line edges and assign each edge to a layer so that no two edges on the same layer cross. The geometric thickness lies between two previously studied quantities, the (graph-theoretical) thickness and the book thickness. We investigate the geometric thickness of the family of complete graphs, {K_n} . We show that the geometric thickness of K_n lies between \lceil (n/5.646)+0.342 \rceil and \lceil n/4 \rceil, and we give exact values of the geometric thickness of K_n for n \le 12 and n \in {15,16}.

Item Type: Conference Paper 10.1007/3-540-37623-2_8 M Methods > M.999 OthersM Methods > M.500 LayeredG Algorithms and Complexity > G.700 LayeringP Styles > P.720 Straight-lineZ Theory > Z.250 GeometryG Algorithms and Complexity > G.999 OthersG Algorithms and Complexity > G.420 CrossingsP Styles > P.480 Layered http://gdea.informatik.uni-koeln.de/id/eprint/287

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Subsections

### 5.9 A Summary of Separation of Variables

After the previous three examples, it is time to give a more general description of the method of separation of variables.

#### 5.9.1 The form of the solution

Before starting the process, you should have some idea of the form of the solution you are looking for. Some experience helps here.

For example, for unsteady heat conduction in a bar of length , with homogeneous end conditions, the temperature would be written

where the are chosen eigenfunctions and the are computed Fourier coefficients of . The separation of variables procedure allows you to choose the eigenfunctions cleverly.

For a uniform bar, you will find sines and/or cosines for the functions . In that case the above expansion for is called a Fourier series. In general it is called a generalized Fourier series.

After the functions have been found, the Fourier coefficients can simply be found from substituting the expression above for in the given partial differential equation and initial conditions. (The boundary conditions are satisfied when you choose the eigenfunctions .) If there are other functions in the partial differential equation or initial conditions, they too need to be expanded in a Fourier series.

If the problem was axially symmetric heat conduction through the wall of a pipe, the temperature would still be written

but the expansion functions would now be found to be Bessel functions, not sines or cosines.

For heat conduction through a pipe wall without axial symmetry, still with homogeneous boundary conditions, the temperature would be written

where the eigenfunctions turn out to be sines and cosines and the eigenfunctions Bessel functions. Note that in the first sum, the temperature is written as a simple Fourier series in , with coefficients that of course depend on and . Then in the second sum, these coefficients themselves are written as a (generalized) Fourier series in with coefficients that depend on .

(For steady heat conduction, the coordinate '' might actually be a second spatial coordinate. For convenience, we will refer to conditions at given values of as initial conditions'', even though they might physically really be boundary conditions.)

#### 5.9.2 Limitations of the method

The problems that can be solved with separation of variables are relatively limited.

First of all, the equation must be linear. After all, the solution is found as an sum of simple solutions.

The partial differential equation does not necessarily have to be a constant coefficient equation, but the coefficients cannot be too complicated. You should be able to separate variables. A coefficient like in the equation is not separable.

Further, the boundaries must be at constant values of the coordinates. For example, for the heat conduction in a bar, the ends of the bar must be at fixed locations and . The bar cannot expand, since then the end points would depend on time.

You may be able to find fixes for problems such as the ones above, of course. For example, the nonlinear Burger's equation can be converted into the linear heat equation. The above observations apply to straightforward application of the method.

#### 5.9.3 The procedure

The general lines of the procedure are to choose the eigenfunctions and then to find the (generalized) Fourier coefficients of the desired solution . In more detail, the steps are:

1. Make the boundary conditions for the eigenfunctions homogeneous

For heat conduction in a bar, this means that if nonzero end temperatures or heat fluxes through the ends are given, you will need to eliminate these.

Typically, you eliminate nonzero boundary conditions for the eigenfunctions by subtracting a function from that satisfies these boundary conditions. Since only needs to satisfy the boundary conditions, not the partial differential equation or the initial conditions, such a function is easy to find.

If the boundary conditions are steady, you can try subtracting the steady solution, if it exists. More generally, a low degree polynomial can be tried, say , where the coefficients are chosen to satisfy the boundary conditions.

Afterwards, carefully identify the partial differential equation and initial conditions satisfied by the new unknown . (They are typically different from the ones for .)

2. Identify the eigenfunctions

To do this substitute a single term into the homogeneous partial differential equation. Then take all terms involving and the corresponding independent variable to one side of the equation, and and the other independent variables to the other side. (If that turns out to be impossible, the partial differential equation cannot be solved using separation of variables.)

Now, since the two sides of the equation depends on different coordinates, they must both be equal to some constant. The constant is called the eigenvalue.

Setting the -side equal to the eigenvalue gives an ordinary differential equation. Solve it to get the eigenfunctions . In particular, you get the complete set of eigenfunctions by finding all possible solutions to this ordinary differential equation. (If the ordinary differential equation problem for the turns out to be a regular Sturm-Liouville problem of the type described in the next section, the method is guaranteed to work.)

The equation for is usually safest ignored. The book tells you to also solve for the , to get the Fourier coefficients , but if you have an inhomogeneous partial differential equation, you have to mess around to get it right. Also, it is confusing, since the eigenfunctions do not have undetermined constants, but the coefficients do. It are the undetermined constants in that allow you to satisfy the initial conditions. They probably did not make this fundamental difference between the functions and the coefficients clear in your undergraduate classes.

There is one case in which you do need to use the equation for the : in problems with more than two independent variables, where you want to expand the themselves in a generalized Fourier series. That would be the case for the pipe wall without axial symmetry. Simply repeat the above separation of variables process for the partial differential equation satisfied by the .

3. Find the coefficients

Now find the Fourier coefficients (or for three independent variables) by putting the Fourier series expansion into the partial differential equation and initial conditions.

While doing this, you will also need to expand the inhomogeneous terms in the partial differential equation and initial conditions into a Fourier series of the same form. You can find the coefficients of these Fourier series using the orthogonality property described in the next section.

You will find that the partial differential equation produces ordinary differential equations for the individual coefficients. And the integration constants in solving those equations follow from the initial conditions.

Afterwards you can play around with the solution to get other equivalent forms. For example, you can interchange the order of summation and integration (which results from the orthogonality property) to put the result in a Green's function form, etcetera.

#### 5.9.4 More general eigenvalue problems

So far, the eigenvalue problems in the examples were of the form . But you might get a different problem in other examples. Usually that produces a different orthogonality expression.

You can figure out what is the correct expression by writing your ordinary differential equation in the standard form of a Sturm-Liouville problem:

where is the eigenfunction to be found and , , and are given functions. The distinguishing feature is that the coefficient of the second, , term is the derivative of the coefficient of the first, term.

Starting with an arbitrary second order linear ordinary differential equation, you can achieve such a form by multiplying the entire ordinary differential equation with a suitable factor.

The boundary conditions may either be periodic ones,

or they can be homogeneous of the form

where , , , and are given constants. Note the important fact that a Sturm-Liouville problem must be completely homogeneous: must be a solution.

If you have a Sturm-Liouville problem, simply (well, simply ...) solve it. The solutions only exists for certain values of . Make sure you find all solutions, or you are in trouble. They will form an infinite sequence of eigenfunctions', say , , , ... with corresponding eigenvalues' , , , ... that go off to positive infinity.

You can represent arbitrary functions, say , on the interval as a generalized Fourier series:

If you know , the orthogonality relation that gives the generalized Fourier coefficients is

Now you know why you need to write your Sturm-Liouville problem in standard form: it allows you to pick out the weight factor that you need to put in the orthogonality relation!


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# Determine resistor values when designing astable multivibrator with BJT

I want to design an astable multivibrator with a frequency of 1 kHz and a duty cycle of 40%.

This is my circuit:

Now, all the references I have tell me how to choose the values of R3, R4, C1 and C2 according to the formula of duty cycle and frequency. But how do I choose R1, R2, R5 and R6?

I have a variable power supply of 0..25 V. I also have two models of BJT available: 2N3904 and BC108.

• I want to use the above mentioned circuit,so that I can obtain a better square wave. If I leave out the diodes,the waveform is not a perfect square wave. Sep 5 '15 at 13:29

In this astable multivibrator

frequency is given by the following formula:

$$f = \frac 1 {ln(2) \times (R_2C_1 + R_3C_2)} \ \approx \frac {1.443} {(R_2C_1 + R_3C_2)}$$

If C1 = C2 = C and R2 = R3 = R:

$$f \approx \frac {0.72} {RC}$$

It just takes a ratio between R2 and R3 to change the cyclic ratio, keeping $$\frac {R_2 + R_3} 2 = R$$

R1 and R4 must be low resistances. Their value won't affect frequency if they're noticeably smaller than the base resistors. Just beware of the maximum collector current.

Sources from Wikipedia.

• How does taking the diodes out affect the waveforms at the collectors? Sep 5 '15 at 11:40
• Just making asymmetric is not my only concern. I need a perfect square wave. Without the diodes it is not possible. Sep 5 '15 at 13:31
• Why not add a buffering stage transistor then? Do you also need two diodes that you need the outputs in phase opposition?
– user59864
Sep 5 '15 at 13:45
• I do not know about buffering stage transistor from the books I have. But,yes,I need them in opposite phases. I need two complementary waveforms. Sep 5 '15 at 13:51
• Indeed using diodes looks like a smart tip to sharpen waveforms. From what I understand the computation I exposed should not differ and give you a sufficiently close approximation of the frequency and ratio. Just that collector resistors (R1/R2 and R5/R6 in your case) should be kept smaller than base resistors and you're good to go.
– user59864
Sep 5 '15 at 13:57

5 years later, and I find this question on Google. So, I'll add my comments for the next guy looking for info.

There's lots of documentation describing the selection of R2 and R3, and the capacitors, but little documentation on the effect of R1 and R4.

I'm playing with my scope and a multivibrator circuit (without steering diodes). I've noticed that my waveform is much more sawtooth shaped than square when I'm using 1k/10nF RC networks and 270R collector resistors (at about 70kHz). However, increasing the RC network to 51k/100pF, and keeping my 270R collector resistors really sharpens up the waveform (at about 150kHz).

Here's the 51k:270R

And with 1k/270R

About the best analysis I can come up with is this (and I might be wrong): These transistors are operating in common-emitter mode. Therefore, gain is proportional to the ratio of the resistors R1:R2 and R4:R3. My transistors (BC337-40) should be capable of a gain of 250, but using 1k:270R sets the max gain permitted to about 4. A higher gain would drive the transistors to the rail (saturation) much faster than a lower gain. So using a 51k/270R configuration sets the gain to ~200 and reduces the rise time, sharpening up the wave.

Think about it this way - as the capacitor comes up to voltage, that increase is multiplied by the gain of the circuit, until it hits your V+ rail (saturation). If the gain is low then the increase is also low, and there's a broader zone where the (capacitor voltage * gain) is still less than V+.

So if your goal is sharp square waves, you should use high beta transistors and the highest ratio of R1/4:R2/3 that you can manage. Steering diodes may or may not be necessary depending on just HOW square you need your wave to be, the frequency, and the particulars of your transistors.


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## Chain Rule vs Product Rule

I have a question more than a problem to answer.
I'm having a difficult time recognizing when to use the product rule and when to use the chain rule.

How do you recognize when to use each, especially when you have to use both in the same problem. Problems like $$y+x^4y^3-5x^6+3y^8-42=0$$ tend to mix me up.
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 Product rule: x times y $$\frac{d}{dx}(xy)=xy'+y$$ Chain rule: 2x+2 raised to the power of 2 $$\frac{d}{dx}(2x+2)^2=2(2x+2)\cdot2$$

 Similar discussions for: Chain Rule vs Product Rule Thread Forum Replies Calculus & Beyond Homework 2 Calculus & Beyond Homework 2 Calculus & Beyond Homework 2 Calculus 8 Calculus 2


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cambrassk3

2022-07-03

I am trying to find the maximum of a hermitian positive definite quadratic form $xQ{x}^{H}$ (where $Q={Q}^{H}$ and all eigenvalues of $Q$ are non-negative) over the complex unit cube $|{x}_{i}|\le 1$, $i=1,\dots ,n$ where $x=\left({x}_{1},{x}_{2},\dots ,{x}_{n}\right)\in {\mathbb{C}}^{n}$.

This is the problem of minimizing a concave function over a convex domain. I have read that this problem is NP-hard but there exist some bounds on the optimum. What global optimization technique would your recommend to tackle this problem numerically? Since I am new to the field of optimization, I would appreciate every answer, thanks!

1s1zubv

Expert


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# Quark Matter 2012

12-18 August 2012
US/Eastern timezone

## Observation of identical "near-side" jet-like correlations in d+Au and Au+Au collisions at low trigger $p_T$ by STAR

16 Aug 2012, 16:00
2h

Poster Jets

Joshua Konzer

### Description

Particle production mechanisms vary with $p_T$. At low $p_T$ soft processes dominate whereas hard processes dominate at higher $p_T$. Experimental data has shown drastic change from d+Au to Au+Au collision in $p_T$ spectra, collective phenomena, and baryon/meson ratio at intermediate $p_T$. This indicates that the relative mixture of particles produced by hard and soft processes differ between Au+Au and d+Au at a given, relatively low $p_T$ (< 2.0GeV). It is therefore expected that the dihadron correlations will differ between d+Au and Au+Au with relatively low trigger particle $p_T$. In this talk we present the near-side jet-like correlations in d+Au and Au+Au collisions at 200 GeV by STAR. The jet-like results are obtained by the difference of small and large \Delta\eta correlations. We report the findings as a function of trigger and associated particle $p_T$, collision centrality, and Event Plane trigger orientation. We find the $/sqrt{S_{NN}}=200$GeV d+Au and Au+Au near-side correlations to be identical even at trigger $p_T$ as low as 1.5 GeV/c. The AMPT and HIJING models do not describe the data. Our results seem to challenge the current understanding of particle production mechanisms in relativistic heavy-ion collisions.

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C2h6o Lewis Structure

Thermo; FAQs; Links. And I can see carbon is in group IV. Lewis structure is based on the octet rule. Get Answer to Consider two different organic compounds, each with the formula C2H6O. The hydrogens will create bonds with the outside carbons and the oxygen will be double bonded to the center carbon. Révisez en Première S : Exercice Modéliser une molécule par une représentation de Lewis avec Kartable  Programmes officiels de l'Éducation nationale. For example, two isomeric Lewis structures can be written for C2H6O and four can be written for HCNO. Molecular Lewis Structure Electronic Hybrid- Molecular Ideal Bond Formula Geometry ization Geometry Angles *PCl5(violate octet rule)CH2O C CC C C2H6O C CC C(CH3OCH3) O OO O C CC C C2H6O CC C C(C2H5OH) CC C C OO O O C6H6(C's form a One C only ring)#9 VSEPR/Molecular Geometry Rev F09NF Fall 2009 Page 10 of 10. Molecular Polarity Chemical Properties Dipole Moment: 1. In a chemical equation, C2H6O + PCl3 --> C2H5Cl + H3PO3, when the reaction was carried out, the actual yield of C2H5Cl was calculated as 97. She has taught science courses at the high school, college, and graduate levels. Ethanol's chemical formula is C 2 H 6 O. Silicon having valence electrons in the 3rd energy level, will also have access to the 4d sublevel, thus allowing for more than 8 electrons. - Carbon and Hydrogen (2. It has a flashpoint of 55°F, is classified as a depressant drug, and. Hydrogen has one valance electrons, Carbon has four, and Oxygen has six. The concept is that valence shell electron pairs are involved in bonding, and that these electron. 4 Related Records. Electrons are placed around each atom so that the octet rule is obeyed. Schéma de Lewis de la molécule Classe de 2nd Chimie II Représentation de Cram : Représenter en relief sur votre feuille les molécules CH4 ; NH3 et C2H6O (aidez vous en construisant la molécule grâce aux modèles moléculaires). Build and Draw ethyl alcohol and dimethyl ether both of these have the formula C2H6O. The word "alcohol" comes from the Arabic term al kohl meaning "the fine powder. Use information from step 4 and 5 to draw the C 2 H 5 OH lewis structure. 2 Lewis Structures. Isobutane is a colorless, odorless, transparent gas. The carbon-oxygen double bond of aldehydes are composed of one sigma() and one pi (π) bond like the double bond of alkenes. In this formula, n is the number of moles, P is the pressure, V is the. So if I look at the molecular formula CH4, which is methane, and I want to draw a dot structure for the methane molecule, I would go over here to my organic periodic table and find carbon. Carbon Dioxide (CO 2). Valence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). The Lewis structure is built for the up and down electrons, separately. Lewis structures represent the valence electrons in an element or atom (electrons in the outmost shell used for bonding to other atoms). Dipole moments of individual conformers (rotational isomers) are given when they have been measured. C:4×2=8 H:1×6=6 O:6. Molecular Lewis Structure Electronic Hybrid- Molecular Ideal Bond Formula Geometry ization Geometry Angles *PCl5(violate octet rule)CH2O C CC C C2H6O C CC C(CH3OCH3) O OO O C CC C C2H6O CC C C(C2H5OH) CC C C OO O O C6H6(C's form a One C only ring)#9 VSEPR/Molecular Geometry Rev F09NF Fall 2009 Page 10 of 10. dimethyl ether (248 K) e. 5 Chemical Vendors. SCl 2 - Sulfur Dichloride: First draw the Lewis dot structure: Then draw the 3D molecular structure using VSEPR rules: The molecular geometry of SCl 2 is bent with asymmetric charge distribution around the central atom. Ethanol (C 2 H 6 O) Molar Mass Oxidation Number. Methane, CH 4 , the simplest organic compound, contains covalent bonds. Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. Add the valence electrons of each element to get the total needed. org) Methoxyethene Propanone (from www. Draw three Lewis structures for C 3 H 8 O. The Lewis structure for C2H6 requires you have a double bond between the Carbon (C) atoms in order to fill the octets of each atom. The Lewis symbols for the atoms are used to account for the bonding in a compound; the resulting representation is called the Lewis formula (or Lewis structure) for the compound. CCl 2 F 2 d. Molécules, schéma de Lewis d'après www. 2 Names and Identifiers. Below, the concept of hybridization is described using four simple organic molecules as examples. Phosphorus pentafluoride is found to have a regular trigonal bipyramidal structure. A Lewis electron dot diagram (or electron dot diagram or a Lewis diagram or a Lewis structure) is a representation of the valence electrons of an atom that uses dots around the symbol of the element. , and thanks for watching. Hybridization is a model that attempts to remedy the shortcomings of simple valence bond theory. The O atom has two. This chemical formula can also be written as CH 3 CH 2 OH or C 2 H 5 OH. if triple then 2 pi and 1 sigma. Ethanol, like all alcohols, has an OH (hydroxylic) group attached to a saturated carbon atom. This is illustrated by the drawings below. The result is called a Lewis structure, or dot structure. It contains six carbon and hydrogen atoms each. The shape of the molecule must be considered as well. Carbon Dioxide (CO 2). And the π bond is formed by the overlap of two unhybridized p. In a similar sense, the two Lewis structures for the SO 2 molecule are in resonance. edu |Chemistry Home. If an internal link led you here, you may wish to change the link to point directly to the intended article. com) And its tautomer, Prop-1-en-2-ol Propanal (from commons. Le schéma de Lewis d'une molécule s'obtient en considérant les pseudo-schémas de Lewis des atomes qui la composent, conformément à sa formule brute. The hydrogen atoms lie outside the ring structure, each connected to a single carbon atom. Lewis dot structure of C 2 H 6. Lewis Dot of Ethanol (Ethyl Alcohol) CH 3 CH 2 OH. Lewis, who. Structure, Geometry, and Polarity of Molecules What you will accomplish in this experiment This experiment will give you an opportunity to draw Lewis structures of covalent compounds, then use those structures to visualize the three-dimensional shapes of the molecules. Équations chimiques balancées. Finally we calculate the smallest whole integer ratios by multiplying each number above by 3 to get. So they're both valid Lewis structures. The molecular formula for ethanol is C 2 H 6 O and its molar mass is 46. Ethanol, or C2H6O, has two different types of bonding between its constituent atoms. Rank C2H6O, C3H8O and C4H^10 O in terms of IMF and explain their structures? neeed heeelppp. BrO3- + N2H4 -----> NO3- + Br –B. Draw two Lewis structures for C2H6O. " Originally, this referred to an antimony sulfide compound (Sb 2 S 3) used for eye shadow. So in the case of water, N = 8 + 2(2) = 12 (8 valence electrons for the oxygen atom, plus 2 each for the two hydrogen atoms) A = 6 + 2(1) = 8 (6 valence electrons for the oxygen atom, plus 1 for each of the two hydrogen atoms). Ethanol's chemical formula is C 2 H 6 O. 118 of the Thermochemical Network This version of ATcT results was partially described in Ruscic et al. A molecular formula shows the number and identity. If there are more electrons than it, then that compound donates the electron. On the unbonded sides, there are five single bonded H atoms and one single bonded O atom. Use lines to indicate bonding pairs, and dots to indicate lone pairs. Sulfur Trioxide Molecular Geometry. isooctane. Lewis structure is based on the octet rule. Draw two Lewis structures for C 2 H 6 O. ethanol (C2H6O, bp 78 degrees C) or 1-propanol (C3H8O, bp 97 degrees C) B. Expand this section. In turn, these polar covalent bonds can lead to hydrogen bonds forming between ethanol. To determine the total number of shared (bonding) and unshared (non-bonding) electrons in a compound use the following rule: S= N-A, where S is the total number of shared electrons, N is the total number of valence shell electrons needed by all the atoms in. C2H4F2 or h. Helmenstine holds a Ph. In Lewis theory, the val. 4 groups = tetrahedral = 109. Consider two different organic compounds, each with the formula C 2 H 6 O. RESONANCE STRUCTURE OF C6H5OH - Chemistry - Organic Chemistry Some Basic Principles and Techniques. 04% C 1 character in a sp2. As a liquid, it is ideal for transport and storage. if triple then 2 pi and 1 sigma. Let's do the Lewis structure for C2H6, ethane. The most famous Kekule structures are what we would now call the two most significant resonance contributors of benzene. For C 2 H 2 you have a total of 10 valence electrons to work with. C3H8 is a linear molecule because it has no specific central atom. Draw good Lewis structures for each of the following: CO NO 2 C 2H 6O (2 isomers) BC 3H 9 (4 isomers) 2. This is called dimethyl ether. C2H6O: UNII Type: INGREDIENT SUBSTANCE: InChIKey: LFQSCWFLJHTTHZ-UHFFFAOYSA-N : Search the web for this InChIKey : NOTE: UNIIs are generated based on scientific identity characteristics using ISO 11238 data elements. 7915 g/mL, is required to produce exactly 1000 kg of MTBE, assuming a 100% yield? Write two complete balanced equations for each of the following reactions, one using condensed formulas and one using Lewis structures. Lewis dot structure of C 2 H 6. in C2H6 all are single bonds hence 7 sigma bonds. The word "alcohol" comes from the Arabic term al kohl meaning "the fine powder. Ethanol | CH3CH2OH or C2H6O | CID 702 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities. Whenever you see a compound made of Carbon and Hydrogen that ends in ane that means it will only have single bonds. Équations chimiques balancées. Draw the Lewis structure for the molecule or ion. The carbon and oxygen both are sp 2 hybridized. In these cases, the entire structure is placed in brackets, and the charge is written as a superscript on the upper right, outside of the bracket. In simple molecules, the atom with the most available sites for bondng is usually placed central. Answer to Draw Lewis structures for (a) Two compounds of formula C4H10 (b) Two compounds of formula C2H6O (c) Two compounds of formula C2H7N (d) Three com. Illustrated Glossary of Organic Chemistry Kekule structure : A Lewis structure in which bonded electron pairs in covalent bonds are shown as lines. A Lewis electron dot diagram (or electron dot diagram or a Lewis diagram or a Lewis structure) is a representation of the valence electrons of an atom that uses dots around the symbol of the element. Based on the VSEPR model, we predict a tetrahedral distribution of electron clouds around carbon, H - C - H and H - C - Cl bond angles of 109. Label all formal charge. In drawing the Lewis structure for C 2 H 2 (also called ethyne) you'll find that you don't have enough valence electrons available to satisfy the octet for each element (if you use only single bonds). Lewis dot structure of C 2 H 6. For the best answers, search on this site https://shorturl. 🤓 Based on our data, we think this question is relevant for Professor Ritchey's class at CSUS. They have the same number of electrons, and a similar length to the molecule. Structural Isomers – Just how many structures can you make from a simple formula? 1. atoms are bonded to each other. - Carbon and Hydrogen (2. And the π bond is formed by the overlap of two unhybridized p. CHAPTER 14 COVALENT BONDING: ORBITALS The Localized Electron Model and Hybrid Orbitals 9. This set index page lists chemical structure articles associated with the same molecular formula. Answer to Draw Lewis structures for (a) Two compounds of formula C4H10 (b) Two compounds of formula C2H6O (c) Two compounds of formula C2H7N (d) Three com. Thus, it is termed 'hydrocarbon'. Hydrogen has one valance electrons, Carbon has four, and Oxygen has six. 1) C2H60- This functional group is alchohol. Silicon having valence electrons in the 3rd energy level, will also have access to the 4d sublevel, thus allowing for more than 8 electrons. nonbonding valence electrons. Counting Regions of High Electron Density. Today, we are going to learn a process by [Filename: L2 - Lewis Structures 6. com) And its tautomer, Prop-1-en-2-ol Propanal (from commons. , in CO2, there are 4 + 6 + 6 = 16 VE 2. Ethanol, a primary alcohol, is an important raw material for the synthesis of various compounds. Reaction Information. Lewis dot structure of C 2 H 6. Other articles where Kekulé structure is discussed: chemical bonding: Resonant structures: …for each of these so-called Kekulé structures. April 27, 2017 Timtech 5 Comments. 04 moles how many grams of C2H5Cl were actually obtained? A) 123 grams B) 128 grams C) 132 grams D) 135 grams E) 138 grams. Draw a Lewis structure for each of the following molecules. Draw the dot structures in between each letter. C2H6O: UNII Type: INGREDIENT SUBSTANCE: InChIKey: LFQSCWFLJHTTHZ-UHFFFAOYSA-N : Search the web for this InChIKey : NOTE: UNIIs are generated based on scientific identity characteristics using ISO 11238 data elements. See the lower right cell in the table above. In the Lewis structure, the central oxygen atom is bonded to two carbon atoms, which have little or no electronegativity. Helmenstine holds a Ph. If the oxygen atom is bonded on the terminal C atoms then it is aldehyde and if it is bonded with the 2nd carbon atom then it is ketone. It will hold more than 8 electrons. The important thing to realize about resonance forms is that they are not necessarily different structures, but they all together defime what a molecule truly looks like! When a compound has a formal charge at a certain location, we indicate that with a plus or minus symbol at that atom. Draw the Lewis dot structure of NO2. The picture to the right shows a Lewis structure of cyclopropane. Structure of the aldehyde. Valence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Answer to Draw Lewis structures for (a) Two compounds of formula C4H10 (b) Two compounds of formula C2H6O (c) Two compounds of formula C2H7N (d) Three com. The result is called a Lewis structure, or dot structure. Ethanol's chemical formula is C 2 H 6 O. Hydrogen has one valance electrons, Carbon has four, and Oxygen has six. (refer to the second picture) in the example, the oxygen on the left has more. Lewis structures, also known as electron dot structures, are named after Gilbert N. En général les erreurs se corrigent par la prise en compte de plusieurs structures de Lewis (comme dans CO 2-), on parle de mésomérie. Note the usual number of bonds each can form. if double bond then one sigma and one pi. Expand this section. Consider the molecule H 2 CO 2. 4 Related Records. 13) (2) and (3) are possible Lewis structures. In ethanol there are two carbon atoms, six hydrogen atoms and one oxygen atoms. Structure and Heats of Formation of Iodine Fluorides and the Respective Closed-Shell Ions from CCSD(T) Electronic Structure Calculations and Reliable Prediction of the Steric Activity of the Free-Valence Electron Pair in ClF6−, BrF6−, and IF6−. 3) : very covalent. The carbomer is added to water in purell by sifting it in. The number of valence electrons correspond to the group in which you find the element. ), (4) determine the shape based on the number of electron groups, and (5) determine the hybridization based on the shape. Additional information for writing Lewis Structures Lewis Structures that Show Bonding between Nonmetals 1. In drawing the Lewis structure for C 2 H 2 (also called ethyne) you'll find that you don't have enough valence electrons available to satisfy the octet for each element (if you use only single bonds). This structure has resonance, so draw all the resonance structures and the resonance hybrid. Strong electron delocalization in your best Lewis structure will also show up as donor-acceptor interactions. A Lewis structure also helps to make a prediction about the geometry of a molecule. Viewing Notes: With C 2 H 6 there are only single bonds. 2 shows four ways of representing a C 4H 10 molecule. Functional groups are also indicators. Thus, it is termed ‘hydrocarbon’. Use information from step 4 and 5 to draw the lewis structure. ethanol (C2H6O, bp 78 degrees C) or 1-propanol (C3H8O, bp 97 degrees C) B. Search our 100 + Lewis Structures (Opens New Window) See the Big List of Lewis Structures : Frequently Tested Lewis Structures Basic CH 4, NH 3, C 2 H 4, O 2, N 2 Intermediate. Lewis structure: The properly way to determine the Lewis structure, based on this example, is: Total valence electrons: $4 + 6\cdot2 + 1\cdot2 = 18$ Total electrons needed for octets/doublets: $8\cdot3+2\cdot2 = 28$ Total shared/bonding electrons: $28-18 = 10$ (In other words, there are only five bonds. See the following examples for how to draw Lewis dot structures for common atoms involved in covalent bonding. Now, connect the Lewis Dot Structures. , C 6 H 8 O 6, or C9H12O9, or. in C2H6 all are single bonds hence 7 sigma bonds. Isobutane has a tertiary carbon, and it is the simplest molecule with a tertiary carbon. Find more Chemistry widgets in Wolfram|Alpha. The 2D chemical structure image of Vinyl iodide is also called skeletal formula, which is the standard notation for organic molecules. Enter the molecular formula of the molecule. Bond-line structure (bond-line formula, skeletal structure, skeletal formula): A representation of molecular structure in which covalent bonds are represented with one line for each level of bond order. Carbon has four valence electrons, while hydrogen has one valence electron. 1)Find the Lewis structure and the structural formula for these compounds and ions. Draw the Lewis Dot Structure for the. So let's multiply that times 2. if there is a single bond then its always sigma. Both use all 20 valence electrons and achieve full outer shells. By: Sharla Riddle. methane: CH4 C H H H H CH4 C H H condensed formula 2D formula 3D formula methane 2. Structure, properties, spectra, suppliers and links for: Ethanol, Alcohol, 64-17-5, 107-19-7, 110-65-6, 1725-82-2, 2348-46-1, EtOH, C2H5OH. They follow the duet rule (2 electrons). NBr 3 Write Lewis structures for each of the following odd electron molecules: a. Lewis structures represent the valence electrons in an element or atom (electrons in the outmost shell used for bonding to other atoms). Name: Argon Symbol: Ar Atomic Number: 18 Atomic Mass: 39. Structure of the aldehyde. drawing Lewis structures and structural formulas (Chapter 3, sections 3. 1021/ic800021h. hexane (C6H14, bp 69 degrees C) or octane. The 2D chemical structure image of Vinyl iodide is also called skeletal formula, which is the standard notation for organic molecules. Inorganic Chemistry 2008, 47 (12) , 5485-5494. 12 Check here for more information https://www. Draw two Lewis structures for C 2 H 6 O. Shorthand (line) formulas omit the symbols for carbon and hydrogen entirely. One point is earned for the correct Lewis structure. Lewis structure,molecular shape and polarity of the following: C2H6O,C2H6O,C4H8,C2H5CL,CH4,C3H6,HCOOH,CH3NH2. Carbon has four valence electrons, while hydrogen has one valence electron. On the unbonded sides, there are five single bonded H atoms and one single bonded O atom. It has a flashpoint of 55°F, is classified as a depressant drug, and. Counting Regions of High Electron Density. Compounds with the molecular formula C2H6O include: #N#list of chemical structure articles associated with the same molecular formula. Drawing the Lewis Structure for C 2 H 2 (Ethyne or Acetylene). Step 1: Find valence e- for all atoms. The chemical formula of ethanol is given by- Chemical Formula for Ethanol (Ethyl Alcohol) Formula for Ethyl Alcohol. Hybridization in the Best Lewis Structure Down Electrons. They mix to give a hybrid that is more than the sum of its components. 70 More Lewis Dot Structures. Structure and Heats of Formation of Iodine Fluorides and the Respective Closed-Shell Ions from CCSD(T) Electronic Structure Calculations and Reliable Prediction of the Steric Activity of the Free-Valence Electron Pair in ClF6−, BrF6−, and IF6−. The theoretical number of carbon dioxide moles produced from 3 moles C2H6O is _____. And the π bond is formed by the overlap of two unhybridized p. How To: Drawing Lewis Structures From Condensed Molecular Formulas. com) And its tautomer, Prop-1-en-2-ol Propanal (from commons. It is the simplest ketone possible with three carbons in a row with an oxygen doubled bonded to the central carbon atom. Silicon having valence electrons in the 3rd energy level, will also have access to the 4d sublevel, thus allowing for more than 8 electrons. Alternatively a dot method can be used to draw the lewis structure. Lewis, who. 3) C2H6O — are also fairly small. nonpolar (symmetrical distribution of polar bonds) b. This set index page lists chemical structure articles associated with the same molecular formula. Use the interactive menu bar located above to get started. Build and Draw ethyl alcohol and dimethyl ether both of these have the formula C2H6O. -the whole book! available from KrishiKosh, an Institutional Repository of Indian National Agricultural Research System. Since C has 4 valence electrons, and each H atoms contributes 1 valence electron, the total number of electrons will be 2*4 + 6*1 = 14 "e"^(-) This means that the Lewis dot structure for C_2H_6 must account for 14 valence electrons, either through. Molar mass of C2H6O = 46. For each of the following, draw the Lewis Dot Structure, give the electron arrangement (E. Temperature (K) A B C Reference Comment; 194. C2H6O (C-C-O sequence) 7. In a similar sense, the two Lewis structures for the SO 2 molecule are in resonance. Serious Science with an Approach Built for Today's StudentsSmith'sOrganic Chemistrycontinues to breathe new life into the organic chemistry world. 045 moles/0. e- = A group # ⚫except helium, which has 2 val e-. Draw a Lewis structure for each of the following molecules. This rule states that every molecule should have eight electrons in its outer shell of an atom to be stable. [1][2][3] A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. HClO2 (central chlorine, hydrogen attached. There is no Lewis structure of this, because there are at least TWO possible substances with this molecular (NOT structurized) formula C2H6O could be: C2H5OH, or better H3C-CH2(OH) for ethanol or DA: 7 PA: 94 MOZ Rank: 12. Set the grading options for the problem on the lower left: Click a grading setting option to toggle whether or not it will be active. in C2H6 all are single bonds hence 7 sigma bonds. Using the VSEPR theory, and the table above, predict the molecular shapes. Since the molecule is linear, it has 180 degree bond angles. It has two lone-pairs of electrons on the central atom. Counting Regions of High Electron Density. Lewis dot structure of this compound is: Figure 5. It is made of nine atoms that include two carbon (C) atoms, six hydrogen (H) atoms. One point is earned for the correct Lewis structure. (i) Complete the Lewis electron-dot diagram of the molecule in Box X. Ethyl alcohol is a colourless, volatile liquid with a characteristic odor and a pungent taste. The molecular formula for ethanol is C2H6O. They are of the kind in which a question is trying not to repeat structures. NBr 3 Write Lewis structures for each of the following odd electron molecules: a. 286 Chapter 9: Molecular Structures (e) PF5 (40 e The type is AX 5E0, so it is triangular bipyramidal. (1) The simplest alcohol is methanol (prim) (methyl alcohol), molecular formula of (a) (also the empirical formula) and four structural formulae representations: (b) abbreviated structural formulae (c) (d) displayed formulae and (e),. , C makes 4 bonds and O makes 2 bonds 3. (2) and (3)d. Add Your Answer. Sulfur Trioxide Molecular Geometry. The O atom has two pairs of dots and one additional single bond attached to an H atom. If there are multiple elements that have more dots than the rest, then just pick one at random among the higher dotted elements. In this formula, n is the number of moles, P is the pressure, V is the. Carbon->hydrogen is a covalent bond(1) Hydrogen-> oxygen is a covalent and hydrogen bond(1). Expand this section. C2H6O + Cr2O72. Thus, the difference between organic and inorganic chemistry stems from the difference between organic and inorganic compounds, which in turn, depends on the presence or absence of carbon atoms in their structure. Isobutane is a colorless, odorless, transparent gas. A B; What is the shape and polarity of H2? linear, nonpolar: What is the shape and polarity of BeBr2? linear, nonpolar: What is the shape and polarity of BI3?. The most famous Kekule structures are what we would now call the two most significant resonance contributors of benzene. Compounds with the molecular formula C2H6O include: #N#list of chemical structure articles associated with the same molecular formula. -the whole book! available from KrishiKosh, an Institutional Repository of Indian National Agricultural Research System. Why are the intermolecular forces in ethanol stronger than those in ethyl ether? To answer this question, we must look at the molecular structure of these two substances. It contains six carbon and hydrogen atoms each. (Hint: The two Lewis structures in part a are constitutional isomers; they have the same atoms, but differ in the way the atoms are connected; see page 143. So let's multiply that times 2. 5880 × 10^-3. Xef2 Lewis Structure. The chemical formula for ethanol is CH 3 CH 2 OH or C 2 H 5 OH (condensed structural formulas). Ethanol, a primary alcohol, is an important raw material for the synthesis of various compounds. Step 1: Find valence e- for all atoms. We show electrons around the atoms with dots: The number of dots equal to the number of valence electrons an element has. There is no Lewis structure of this, because there are at least TWO possible substances with this molecular (NOT structurized) formula C2H6O could be: C2H5OH, or better H3C-CH2(OH) for ethanol or DA: 7 PA: 94 MOZ Rank: 12. 3) : very covalent. Draw a structure that obeys the. Draw a skeleton for the molecule which connects all atoms using only single bonds. Formula Lewis Electron-Dot Diagram : Ethanethiol CH 3 CH 2 SH : Ethane : CH 3 CH 3: Ethanol CH 3 CH 2 OH : Ethyne : C 2 H 2 (a) Draw the complete Lewis electron-dot diagram for ethyne in the appropriate cell in the table above. Triple bonds are the strongest, and double the second strongest. If there are multiple elements that have more dots than the rest, then just pick one at random among the higher dotted elements. H2SO4 + HI -----> H2S + I2 + H2OC. Lewis structures are a simple and the most common way we represent molecules. How to Draw the Lewis dot structures for 2 types of. Setarakan reaksi redoks di bawah ini :A. If you look at the geometry of the tetrahedron, you see that this puts the nitrogen directly opposite the hydrogen. Another way of writing this molecular formula is CH 3-O-CH 3. There are four carbons joined up in a row, with a CH 3 group attached to the next-to-end one. 0 atm pressure of oxygen is 0. Valence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Get the free "Lewis structure" widget for your website, blog, Wordpress, Blogger, or iGoogle. The salts produced by this reactions are neutral and when they are dissolved in water they behave as electrolytes and conduct electricity. (2) is called dimethyl ether while (3) is called ethanol. In this video, we're going to look at how to draw dot structures of simple organic molecules that have single bonds. Step method to draw the Lewis dot structure of C2H5OH, ethanol, ethyl alcohol. This set index page lists chemical structure articles associated with the same molecular formula. The Lewis dot structure for C2H6O begins with two C atoms singly bonded to each other. Three are two ways to draw the Lewis structure for C2H6O. They mix to give a hybrid that is more than the sum of its components. Hydrogen (H) atoms always go on the outside of a Lewis structure. One of these compounds is a liquid at room conditions and the other is a gas. Now, connect the Lewis Dot Structures. If an internal link led you here, you may wish to change the link to point directly to the intended article. Chart and Diagram Slides for PowerPoint - Beautifully designed chart and diagram s for PowerPoint with visually stunning graphics and animation effects. CHAPTER 14 COVALENT BONDING: ORBITALS The Localized Electron Model and Hybrid Orbitals 9. Lewis Structures Neutral Species 1: Obey Octet Rule Description: 3 groups = (trigonal) planar = 120. C:4×2=8 H:1×6=6 O:6. The Lewis structure is complete when we connect the dots to show the sharing of electron pairs between different atoms. Molecular Weight: Expand this section. condensation3. Ethanol (C2H6O) is combusted with oxygen to produce carbon dioxide and wateraccording to the following reaction: C2H6O + 3O2 -----> 2H2O + 3CO2 If 50g of ethanol is combusted, determine the volume of carbon dioxide that will be produced if the temperature. Lewis dot structures can be drawn to show the valence electrons that surround an atom itself. C2H4F2 or h. Draw two Lewis structures for C 2 H 6 O. But the oxidation state formalism helps us keep track of where the electrons are going, which will come in handy very soon). (a) Using Lewis structures, write the chemical equation representing the reaction. 🤓 Based on our data, we think this question is relevant for Professor Ritchey's class at CSUS. The O atom has two. if triple then 2 pi and 1 sigma. Expand this section. There are multiple single and double bonds throughout the naproxen molecule. Ethylamine-15N, 98 atom % 15N. What do you mean by the strongest C-H bonds? Do you meant he highest bond order?. The Lewis formula for. The three Lewis structures in part b arc also constitutional isomers. They fill the outer shells for each of the atoms in the C2H6O structure. 3 More Lewis Structures. Explain why one of these structures is non-polar and the other 2 are polar. The middle carbon has two hydrogens bonded to it, while the two end carbons have three hydrogens bonded. Ethanol, or C2H6O, has two different types of bonding between its constituent atoms. 118 of the Thermochemical Network This version of ATcT results was partially described in Ruscic et al. Title: Lewis Structures and Molecular Geometry 1 Lewis Structures and Molecular Geometry 2 Drawing Lewis Structures. In Lewis theory, the val. They follow the duet rule (2 electrons). 9995 electrons __has 34. , 1941: Coefficents calculated by NIST from author's data. Alternatively a dot method can be used to draw the C 2 H 5 OH Lewis structure. Thus, it is termed ‘hydrocarbon’. 948 amu Melting Point:-189. ChemDoodle Web Components allow the wielder to present publication quality 2D and 3D graphics and animations for chemical structures, reactions and spectra. Its molecular formula is C6H6. What's the lewis structure for 2H2O? What's the percent composition of 2H2+O2--> 2H2O? Update: For the percent composition would you divide h2 /h20 and o2/h2o? For 2H2O would the lewis structure look any different if it was just an H2O lewis structure, if so how would it look? Answer Save. Several worked examples relevant to this procedure were given in previous posts please see the Sitemap - Table of Contents (Lewis Electron Dot Structures). Multiple Choice. Calculate the number of moles of gas. Why does HF have a higher BP than NH3? Doesn't NH3 form more H bonds than HF? Same goes for CH4. Inorganic Chemistry 2008, 47 (12) , 5485-5494. Problem: Which of the following are possible Lewis structures for C2H6O?a. Complete vibrational assignments are made in terms of the normal modes and thermodynamic functions are evaluated for PCl 5, PCl 3 F 2, and PF 5. For neutral molecules, indicate whether they are polar or nonpolar. Pure ethanol is used as solvent for esters, medicines, solvent based paints and perfumes. General rules for drawing Lewis structure. (1) and (3)c. The carbon and oxygen both are sp 2 hybridized. 70 More Lewis Dot Structures. Drawing the Lewis Structure for C 2 H 2 (Ethyne or Acetylene). Available evidence supports the C2v structure in which the fluorine atoms appear in one equatorial and two axial sites. Determine the total number of valence electrons from all of the atoms in the molecule or ion. 2b is the Lewis structure, which shows all atoms in a plane and all angles at 90o. 15 g/mol, exact mass: 88. The carbon-oxygen double bond of aldehydes are composed of one sigma() and one pi (π) bond like the double bond of alkenes. (2) and (3)d. Rank these in order of increasing freezing points: C2H6O, NaCl, NaSO4, C12H22O11 I suggest that you look them up. Formula Lewis Electron-Dot Diagram : Ethanethiol CH 3 CH 2 SH : Ethane : CH 3 CH 3: Ethanol CH 3 CH 2 OH : Ethyne : C 2 H 2 (a) Draw the complete Lewis electron-dot diagram for ethyne in the appropriate cell in the table above. com) And its tautomer, Prop-1-en-2-ol Propanal (from commons. ; Remember that Hydrogen (H) atoms always go on the outside of a Lewis Structure. La estructura de Lewis es toda aquella representación de los enlaces covalentes dentro de una molécula o un ion. This is illustrated by the drawings below. This sharing allows each atom to achieve its octet of electrons and greater stability. , C makes 4 bonds and O makes 2 bonds 3. Remember the empirical formula has the smallest whole integer ratios, the molecular formula can be different, e. In a similar sense, the two Lewis structures for the SO 2 molecule are in resonance. And I can see carbon is in group IV. 2 The names and structures of aliphatic alcohols C n H 2n+1 OH (and isomeric ethers). Each carbon has to hybridize one 2s and three 2p. Why does HF have a higher BP than NH3? Doesn't NH3 form more H bonds than HF? Same goes for CH4. how many double bonds - 9600155. In the structure above, the alcohol on the second carbon is behind the page. Even simpler than condensed structures are skeletal or line structures: There are a range of structures used to represent organic compounds:. Remember, the # of val. Electron Configuration, Lewis Dot Structure, and Molecular Shape Ele In water, two hydrogen atoms are connected to an oxygen atom, and the. Valence electronic structures can be visualized by drawing Lewis symbols (for atoms and monatomic ions) and Lewis structures (for molecules and polyatomic ions). Why are the intermolecular forces in ethanol stronger than those in ethyl ether? To answer this question, we must look at the molecular structure of these two substances. They can also be used to confirm if the molecular and ionic composition of a chemical formula is reasonable. (2) is called dimethyl ether while (3) is called ethanol. Now, connect the Lewis Dot Structures. The important thing to realize about resonance forms is that they are not necessarily different structures, but they all together defime what a molecule truly looks like! When a compound has a formal charge at a certain location, we indicate that with a plus or minus symbol at that atom. 5 Chemical Vendors. 784 g/cm 3 Color: Colorless Gas Atomic Structure. Now draw, an H above and below both C. Formal Charge. The result is called a Lewis structure, or dot structure. 2b is the Lewis structure, which shows all atoms in a plane and all angles at 90o. The hydrogen-oxygen and carbon-oxygen bonds are polar covalent bonds. This is not the case. Compound Description Examples. Label all formal charge. Calculate the total valence electrons in the molecule. Lewis, Gilbert Newton. Search our 100 + Lewis Structures (Opens New Window) See the Big List of Lewis Structures : Frequently Tested Lewis Structures Basic CH 4, NH 3, C 2 H 4, O 2, N 2 Intermediate. Drawing the Lewis Structure for C 2 H 2 (Ethyne or Acetylene). ethanol (C2H6O, bp 78 degrees C) or 1-propanol (C3H8O, bp 97 degrees C) B. Other articles where Kekulé structure is discussed: chemical bonding: Resonant structures: …for each of these so-called Kekulé structures. For example, two isomeric Lewis structures can be written for C2H6O and four can be written for HCNO. A) 6 The Lewis structure for carbon monoxide is :C three O: This structure shows B) 2 lone pains and 3 bonding pairs. The O atom has two. Determine the total number of valence electrons from all of the atoms in the molecule or ion. e- = A group # ⚫except helium, which has 2 val e-. Drawing the Lewis Structure for C 2 H 6 - Ethane. (a) The skeletal structure for one of the two compounds is shown below in Box X. ETHANOL reacts violently with acetyl chloride and acetyl bromide [Rose, (1961); Merck 11th ed. En général les erreurs se corrigent par la prise en compte de plusieurs structures de Lewis (comme dans CO 2-), on parle de mésomérie. Practice Problems on Lewis Structures 1. This is illustrated by the drawings below. The lobes of the p orbitals are The Lewis structure is: The carbon atoms are sp3 hybridized. (Hint: The two Lewis structures in part a are constitutional isomers; they have the same atoms, but differ in the way the atoms are connected; see page 143. The word "alcohol" comes from the Arabic term al kohl meaning "the fine powder. For homework help in math, chemistry, and physics: www. if triple then 2 pi and 1 sigma. 74 °F) Boiling Point:-186. A Lewis structure also helps to make a prediction about the geometry of a molecule. If the p orbitals were used to form bonds, then all bond angles shoud be 90E or 180E. Benzene, a constituent of crude oil, is an organic chemical compound. All the elements that make up ethanol are non-metals therefore making ethanol a covalent compound. ChemDoodle provides you with all the tools to build perfect figures of Lewis Dot Structures. Structures like those shown in Figure 13. They are any structure that have the same constitutional structure! (have the same atoms bonded to the same atoms)! but are arranged differently in three dimensions! Differ in the ORIENTATION of atoms in space! Have already seen this with cis and trans ring structures! The difference in orientation can cause vastly different properties for the molecule!. The Lewis formula for. The bond angles between the carbons are 60 degrees while the bond angles between the hydrogen are 115 degrees. This rule states that every molecule should have eight electrons in its outer shell of an atom to be stable. To determine the Lewis structures, use the periodic. One of these compounds is a liquid at room conditions and the other is a ga. Draw three Lewis structures for C3H8O. 12 Check here for more information https://www. First, draw the lewis dot structures of each. In simple molecules, the atom with the most available sites for bondng is usually placed central. 2) it could be either ketone or aldehyde as they are functional group isomers. The names in bold are the preferred IUPAC ketone name. Therefore this molecule is polar. C:8x2=16 H:2x6=12 O:8 T. Since all the atoms are in either period 1 or 2, this molecule will adhere to the octet rule. Isomers are particularly common among compounds of C, N, and O. C2H6O + Cr2O72. propane (231 K) d. 70 More Lewis Dot Structures. Draw the Lewis structure for the nitrogen atom, nitrogen molecule and ammonia. A bonding orbital for C1-O2 with 0. tutor-homework. The number 0. Drawing Lewis structures from condensed structural formulas is a survival skill for organic chemistry students. (1) The simplest alcohol is methanol (prim) (methyl alcohol), molecular formula of (a) (also the empirical formula) and four structural formulae representations: (b) abbreviated structural formulae (c) (d) displayed formulae and (e),. See the following examples for how to draw Lewis dot structures for common atoms involved in covalent bonding. Ethanol has 2 carbon atoms, 5 hydrogen atoms, and an OH group. The way CH3COCH3 is written gives the Lewis Structure. Hydrogen has one valance electrons, Carbon has four, and Oxygen has six. 12 Check here for more information https://www. Lewis, who. org) And its two tautomeric isomers (Z)-Prop-1-en-1-ol and (E)-Prop-1-en-1-ol Then we have Cyclopropanol Oxetane (R)-Methyloxirane (S)-Methyloxirane And that makes 11 isomers!. And then Hydrogen, group 1, one valence electron; we have 6, multiply that by 6, for a total of 14 valence electrons to work with. Calculate the total valence electrons in the molecule. This diagram shows the conceptual stages of drawing the Lewis structure for a molecule of carbon dioxide (CO2). Draw good Lewis structures for each of the following: CO NO 2 C 2H 6O (2 isomers) BC 3H 9 (4 isomers) 2. Formula Lewis Electron-Dot Diagram : Ethanethiol CH 3 CH 2 SH : Ethane : CH 3 CH 3: Ethanol CH 3 CH 2 OH : Ethyne : C 2 H 2 (a) Draw the complete Lewis electron-dot diagram for ethyne in the appropriate cell in the table above. In Lewis theory, the val. Building the Lewis structures for this molecule reveals the two possibilities … Constitutional Isomers Read More ». This set index page lists chemical structure articles associated with the same molecular formula. if there is a single bond then its always sigma. The chemical structure of the molecule expressed by the doted lone pair of electron and bands are called as Lewis structure. Consider two different organic compounds, each with the formula C 2 H 6 O. If there are multiple elements that have more dots than the rest, then just pick one at random among the higher dotted elements. 1021/ic800021h. The hydrogen-oxygen and carbon-oxygen bonds are polar covalent bonds. The shape of the molecule must be considered as well. Lone pairs, unpaired electrons, and single, double, or triple bonds are used to indicate where the valence electrons are located around each atom in a Lewis structure. Electrons are placed around each atom so that the octet rule is obeyed. Lewis Dot Structure Worksheet. A concept know as formal charge can help us choose the most plausible Lewis structure where there are a number of structures which would all be satisfactory according to the rules used thus far. Two Lewis structures or electron dot diagrams for the nitrite ion. Remember that two electrons go in the first s shell, two. In the Lewis structure, the central oxygen atom is bonded to two carbon atoms, which have little or no electronegativity. this structure, the molecule is polar or nonpolar. [1][2][3] A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. Ethanol (CH 3 CH 2 OH), CAS 64-17-5, commonly known as ethyl alcohol or EtOH, is a clear, volatile, and highly flammable liquid. (include all nonzero formal charges). In these cases, the entire structure is placed in brackets, and the charge is written as a superscript on the upper right, outside of the bracket. O2 O₂ Oxygen Gas Oxygen Molecular Oxygen Oxygen O-17. If an internal link led you here, you may wish to change the link to point directly to the intended article. Triple bonds are the strongest, and double the second strongest. The flashcards below were created by user Anonymous on FreezingBlue Flashcards. 022189 is correctly rounded to two significant figures the number becomes. Predicting Molecular Geometry • The following rules and figures will help discern electron pair arrangements. Molar Mass Bond Polarity Oxidation Number. On the periodic table, Carbon is in group 4 or 14, so it has 4 valence electrons, but we have 2 of them. It would be a CH3-CO-CH3 with all 3 carbons bonding with each other. The O atom has two. This diagram shows the conceptual stages of drawing the Lewis structure for a molecule of carbon dioxide (CO2). This set index page lists chemical structure articles associated with the same molecular formula. And then Hydrogen, group 1, one valence electron; we have 6, multiply that by 6, for a total of 14 valence electrons to work with. Draw the dot structures in between each letter. Rated in order from strongest to weakest these forces are: Ionic > Hydrogen bond > Dipole > van der Waals forces. Flasks and beakers filled with bio fuels, shot on textured metal lab table with space for copy. The Lewis symbols for the atoms are used to account for the bonding in a compound; the resulting representation is called the Lewis formula (or Lewis structure) for the compound. The end product found is H 2O i. So let's multiply that times 2. in biomedical sciences and is a science writer, educator, and consultant. Get the free "Lewis structure" widget for your website, blog, Wordpress, Blogger, or iGoogle. In addition, redrawn chemical structures and artwork help students visualize important chemical concepts, a greater emphasis on biologically-related chemistry (including new problems) helps them grasp the enormous importance of organic chemistry in understanding the reactions that occur in living organisms, and new End ofChapter problems keyed to OWL allow them to work text-specific problems online. Draw a structure that obeys the. There is no Lewis structure of this, because there are at least TWO possible substances with this molecular (NOT structurized) formula C2H6O could be: C2H5OH, or better H3C-CH2(OH) for ethanol or DA: 78 PA: 33 MOZ Rank: 43. Structural Formula. Draw good Lewis structures for each of the following: CO NO 2 C 2H 6O (2 isomers) BC 3H 9 (4 isomers) 2. Ethanol | CH3CH2OH or C2H6O | CID 702 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities. I thought the lone pair would push the other atoms closer together and result in a slightly smaller bond angle. A) 6 The theoretical number of moles of water produced from 2 moles of C2H6O is _______. Draw Lewis structures for : (a) two compounds of formula C4H10 (b) two compounds of formula C2H6O (c) two compounds of formula C2H7N (d) three compounds of formula C2H7NO (e) three compounds of formula C3H8O2 (f) three compounds of formula C2H4O. Determine the total number of valence electrons in a molecule 2. The important thing to realize about resonance forms is that they are not necessarily different structures, but they all together defime what a molecule truly looks like! When a compound has a formal charge at a certain location, we indicate that with a plus or minus symbol at that atom. Video: Drawing the Lewis Structure for Acetone Acetone is a member of the Ketone family of organic compounds. The salts produced by this reactions are neutral and when they are dissolved in water they behave as electrolytes and conduct electricity. Hydrogen bond: The weaker bond between electro negative atom of one molecule and hydrogen atom of another molecule is called hydrogen bond. If you look at the geometry of the tetrahedron, you see that this puts the nitrogen directly opposite the hydrogen. 7 Classification. Problem: Which of the following are possible Lewis structures for C2H6O?a. 1, 2] enthalpy of formation based on version 1. A Lewis base is a species with an available (reactive) pair of electrons and a Lewis acid is an electron pair acceptor. Posted by 8 years ago. In turn, these polar covalent bonds can lead to hydrogen bonds forming between ethanol. Since these take up a lot of space, condensed structural formulas are used. As a liquid, it is ideal for transport and storage. In the structure above, the alcohol on the second carbon is behind the page. Draw three Lewis structures for C 3 H 8 O. Utilisation. So if I look at the molecular formula CH4, which is methane, and I want to draw a dot structure for the methane molecule, I would go over here to my organic periodic table and find carbon. This diagram shows the conceptual stages of drawing the Lewis structure for a molecule of carbon dioxide (CO2). In a chemical equation, C2H6O + PCl3 --> C2H5Cl + H3PO3, when the reaction was carried out, the actual yield of C2H5Cl was calculated as 97. For the Lewis structure for Acetone, calculate the total number of valence electrons for the Acetone molecule. Note that the C2H6 Lewis structure is frequently used on tests. This is a very common problem type seen at the beginning of a course in organic chemistry, and as such they have a sneaky way making it onto exams. Consider the molecule H 2 CO 2. The O atom has two. Of course, they also need to understand that, for example, dimethyl ether and ethanol are not resonance. Why are the intermolecular forces in ethanol stronger than those in ethyl ether? To answer this question, we must look at the molecular structure of these two substances. Examples: C6H12O6, PO4H2(CH2)12CH3. Lewis Structures and Molecular Geometry - Ball & Stick (Shapes) Std 2F. Lewis Structures, Shapes, and Polarity W 319 Everett Community College Student Support Services Program Draw Lewis structures, name shapes and indicate polar or non-polar for the following molecules: a. Isomers are particularly common among compounds of C, N, and O. Since the molecule is linear, it has 180 degree bond angles. Predicting Molecular Geometry • The following rules and figures will help discern electron pair arrangements. On the unbonded sides, there are five single bonded H atoms and one single bonded O atom. , C makes 4 bonds and O makes 2 bonds 3. Draw a Lewis structure for each of the following molecules. Lewis Structures Continued • In drawing a Lewis structure for a molecule with several atoms, sometimes more than one arrangement of atoms is possible for a given molecular formula. beginning students sometimes just need to be told what the connectivity is. The Lewis dot structure for C2H6O begins with two C atoms singly bonded to each other. Ethane is a saturated molecule. Molecular Lewis Structure Electronic Hybrid- Molecular Ideal Bond Formula Geometry ization Geometry Angles *PCl5(violate octet rule)CH2O C CC C C2H6O C CC C(CH3OCH3) O OO O C CC C C2H6O CC C C(C2H5OH) CC C C OO O O C6H6(C's form a One C only ring)#9 VSEPR/Molecular Geometry Rev F09NF Fall 2009 Page 10 of 10. The Lewis structure for C2H6 requires you have a double bond between the Carbon (C) atoms in order to fill the octets of each atom. Hydrogen has one valance electrons, Carbon has four, and Oxygen has six. Each carbon has to hybridize one 2s and three 2p. IF YOUR FORMULA IS CORRECT "C"_2"H"_6 has an sp^3 hybridization on each carbon because of the four electron groups surrounding each carbon. Draw the dot structures in between each letter. The O atom has two pairs of dots and one additional single bond attached to an H atom. Draw Lewis structures for : (a) two compounds of formula C4H10 (b) two compounds of formula C2H6O (c) two compounds of formula C2H7N (d) three compounds of formula C2H7NO (e) three compounds of formula C3H8O2 (f) three compounds of formula C2H4O. Structure of the aldehyde. A molecular formula shows the number and identity. The molecular formula of ethanol is C2H6O, indicating that ethanol contains two carbons and an oxygen. Inorganic Chemistry 2008, 47 (12) , 5485-5494. Temperature (K) A B C Reference Comment; 194. e- of A group elements are represented as dots surrounding the symbol of the element. Use the interactive menu bar located above to get started. In this formula, n is the number of moles, P is the pressure, V is the. Sample Exercise 11C: Draw the Lewis structure, name the molecular geometry (shape), draw a three-dimensional sketch, indicate the bond angle, and state whether each of the following molecules is polar or nonpolar: (a) BCl 3 (b) CH 2 F 2 (c) HCN. (2) and (3)d. Three are two ways to draw the Lewis structure for C2H6O. The two structures on the left are fairly obviously the same - all we've done is flip the molecule over. The first step in drawing the Lewis dot structure for ethane (C_2H_6) is to determine how many valence electrons are available for the molecule. The Lewis dot structure for C2H6O begins with two C atoms singly bonded to each other. Get Answer to Structural isomers are compounds that have the same chemical formula but the atoms are bonded together differently giving different compounds. The concept is that valence shell electron pairs are involved in bonding, and that these electron. Isomers are particularly common among compounds of C, N, and O. e- = A group # ⚫except helium, which has 2 val e-.
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text:
Activity: Representations of the Infinite Square Well

Quantum Fundamentals 2022 (3 years)
• group Small Group Activity schedule 120 min. build Tabletop Whiteboard with markers, Computers with Maple, Voltmeter, Coordinate Axes, A handout for each student description Student handout (PDF)

Representations of the Infinite Square Well

Consider three particles of mass $m$ which are each in an infinite square well potential at $0<x<L$.

The energy eigenstates of the infinite square well are:

$E_n(x) = \sqrt{\frac{2}{L}}\sin{\left(\frac{n \pi x}{L}\right)}$

with energies $E_n = \frac{n^2 \pi^2 \hbar^2}{2mL^2}$

The particles are initially in the states, respectively: \begin{eqnarray*} |\psi_a(0)\rangle &=& A \Big[ 2i \left|{E_4}\right\rangle - 3\left|{E_{10}}\right\rangle \Big]\\[6pt] \psi_b(x,0) &=& B \left[ i \sqrt{\frac{8}{L}}\sin{\left(\frac{4\pi x}{L}\right)} - \sqrt{\frac{18}{L}}\sin{\left(\frac{10\pi x}{L}\right)} \right]\\[6pt] \psi_c(x,0) &=& C x(x-L) \end{eqnarray*}

For each particle:

1. Determine the normalization constant.
2. At $t=0$ what is the probability of measuring the energy of the particle to be $\frac{8\pi^2\hbar^2}{mL^2}$?
3. Find state of the particle at a later time $t$.
4. What is the probability of measuring the energy of the particle to be the same value $\frac{8\pi^2\hbar^2}{mL^2}$ at a later time $t$?
5. What is the probability of finding the particle to be in the first half of the well?

• assignment Wavefunctions

assignment Homework

Wavefunctions
Quantum Fundamentals 2022 (2 years)

Consider the following wave functions (over all space - not the infinite square well!):

$\psi_a(x) = A e^{-x^2/3}$

$\psi_b(x) = B \frac{1}{x^2+2}$

$\psi_c(x) = C \;\mbox{sech}\left(\frac{x}{5}\right)$ (“sech” is the hyperbolic secant function.)

In each case:

1. normalize the wave function,
2. plot the wave function using Mathematica or other computer plotting tool (be sure to include the code you used and label your plots/axes appropriately),
3. find the probability that the particle is measured to be in the range $0<x<1$.

• assignment Quantum concentration

assignment Homework

Quantum concentration
bose-einstein gas statistical mechanics Thermal and Statistical Physics 2020 Consider one particle confined to a cube of side $L$; the concentration in effect is $n=L^{-3}$. Find the kinetic energy of the particle when in the ground state. There will be a value of the concentration for which this zero-point quantum kinetic energy is equal to the temperature $kT$. (At this concentration the occupancy of the lowest orbital is of the order of unity; the lowest orbital always has a higher occupancy than any other orbital.) Show that the concentration $n_0$ thus defined is equal to the quantum concentration $n_Q$ defined by (63): $$n_Q \equiv \left(\frac{MkT}{2\pi\hbar^2}\right)^{\frac32}$$ within a factor of the order of unity.
• assignment One-dimensional gas

assignment Homework

One-dimensional gas
Ideal gas Entropy Tempurature Thermal and Statistical Physics 2020 Consider an ideal gas of $N$ particles, each of mass $M$, confined to a one-dimensional line of length $L$. The particles have spin zero (so you can ignore spin) and do not interact with one another. Find the entropy at temperature $T$. You may assume that the temperature is high enough that $k_B T$ is much greater than the ground state energy of one particle.
• assignment Spin Fermi Estimate

assignment Homework

Spin Fermi Estimate
Quantum Fundamentals 2022 The following two problems ask you to make Fermi estimates. In a good Fermi estimate, you start from basic scientific facts you already know or quantities that you can reasonably estimate based on your life experiences and then reason your way to estimate a quantity that you would not be able guess. You may look up useful conversion factors or constants. Use words, pictures, and equations to explain your reasoning:
1. Imagine that you send a pea-sized bead of silver through a Stern-Gerlach device oriented to measure the z-component of intrinsic spin. Estimate the total z-component of the intrinsic spin of the ball you would measure in the HIGHLY improbable case that every atom is spin up.
2. Protons, neutrons, and electrons are all spin-1/2 particles. Give a (very crude) order of magnitude estimate of the number of these particles in your body.
• group Time Evolution of a Spin-1/2 System

group Small Group Activity

30 min.

Time Evolution of a Spin-1/2 System
Quantum Fundamentals 2022 (3 years)

In this small group activity, students solve for the time dependence of two quantum spin 1/2 particles under the influence of a Hamiltonian. Students determine, given a Hamiltonian, which states are stationary and under what circumstances measurement probabilities do change with time.
• assignment Ideal gas in two dimensions

assignment Homework

Ideal gas in two dimensions
Ideal gas Entropy Chemical potential Thermal and Statistical Physics 2020
1. Find the chemical potential of an ideal monatomic gas in two dimensions, with $N$ atoms confined to a square of area $A=L^2$. The spin is zero.

2. Find an expression for the energy $U$ of the gas.

3. Find an expression for the entropy $\sigma$. The temperature is $kT$.

• face Fermi and Bose gases

face Lecture

120 min.

Fermi and Bose gases
Thermal and Statistical Physics 2020

These lecture notes from week 7 of Thermal and Statistical Physics apply the grand canonical ensemble to fermion and bosons ideal gasses. They include a few small group activities.
• group Quantum Expectation Values

group Small Group Activity

30 min.

Quantum Expectation Values
Quantum Fundamentals 2022 (3 years)
• keyboard Sinusoidal basis set

keyboard Computational Activity

120 min.

Sinusoidal basis set
Computational Physics Lab II 2022

Students compute inner products to expand a wave function in a sinusoidal basis set. This activity introduces the inner product for wave functions, and the idea of approximating a wave function using a finite set of basis functions.
• assignment Unknowns Spin-1/2 Brief

assignment Homework

Unknowns Spin-1/2 Brief
Quantum Fundamentals 2022 (2 years) With the Spins simulation set for a spin 1/2 system, measure the probabilities of all the possible spin components for each of the unknown initial states $\left|{\psi_3}\right\rangle$ and $\left|{\psi_4}\right\rangle$.
1. Use your measured probabilities to find each of the unknown states as a linear superposition of the $S_z$-basis states $\left|{+}\right\rangle$ and $\left|{-}\right\rangle$.
2. Articulate a Process: Write a set of general instructions that would allow another student in next year's class to find an unknown state from measured probabilities.
3. Compare Theory with Experiment: Design an experiment that will allow you to test whether your prediction for each of the unknown states is correct. Describe your experiment here, clearly but succinctly, as if you were writing it up for a paper. Do the experiment and discuss your results.
4. Make a Conceptual Connection: In general, can you determine a quantum state with spin-component probability measurements in only two spin-component-directions? Why or why not?

Learning Outcomes