The Periodic Table

2:29 AM

Hey so guys..one of my answers earned a few down votes, don't know why.,if it is wrong, I'd like to fix it or delete it altogether because I don't want to spread misinformation

Since downvoters did not give a reason, I don't know if this is the case..i mean I thought I was right and which is why I posted it. So is it okay to delete posts for this reason?

The post in question is this one

1

Q: Significant figures in pH calculations: does pH 0.30 count as 2 or 3 significant figures?

Just say I wanted to give a pH calculation to three significant figures. Eg: the $\mathrm{pH}$ of a $0.500 M$ solution of $\ce{HCl}$ is $-\log(0.5) = 0.3010299957...$ Would 3 s.f. be $0.301$ or $0.30$? I know normally when zero comes before a number, it isn't considered a significant number (...

ph

It had two downvoters and one upvote, if I get another downvote might just delete it to earn peer pressure haha

user228700

3:47 AM

Hi everyone :-)

user228700

I'm learning Hückel's rule for aromaticity and I'm trying to figure out if furan is aromatic or not.

user228700

I've been trying to figure out the hybridization of the oxygen atom in furan. Since there are two lone pairs and it is bonded to tao carbon atoms, the steric number comes out to be 4, hence $sp^3$, yeah?

user228700

Apparently, it's actually $sp^2$. How come?

user228700

user228700

?!

user228700

4:12 AM

Okay, I found this:

user228700

7

Q: Hybridization of the oxygen in furan?

I fail to understand why the hybridization of oxygen in furan is $\ce{sp^2}$. I think that since there are 2 bond pairs and two lone pairs so it should be $\ce{sp^3}$ hybridized? Is it to do with the aromaticity of furan? Please help

electronic-configuration orbitals hybridization

user228700

But my next question is, how to know which pairs of electrons are delocalized and which aren't?

user228700

4:31 AM

Oh, never mind, I found this and it clears it right up:

user228700

google.co.in/url?sa=t&source=web&rct=j&url=http://…

DHMO

4:58 AM

@Kaumudi The right hand side diagram is the most misleading diagram I have ever seen

user228700

5:21 AM

Huh.

user228700

Anyhoo, I was wondering about Annulene:

Anonymous

tell

user228700

This compound is not aromatic due to torsional strain.

user228700

But I don't really get how that works; forgive me, I've only just started OC.

user228700

5:24 AM

The hydrogen atoms on the 2nd and 7th carbon atoms want to occupy the same position, causing torsional strain.

Anonymous

yes because of steric interactions

Anonymous

it doesnt remain planar

Anonymous

Cyclodecapentaene or [10]annulene is an annulene with molecular formula C10H10. This organic compound is a conjugated 10 pi electron cyclic system and according to Huckel's rule it should display aromaticity. It is not aromatic, however, because of a combination of steric strain and angular strain.

user228700

OK, but I'm unable to understand why they want to occupy the same position :/

Anonymous

5:26 AM

see because of the hydrogens

Anonymous

in the third picture

Anonymous

it cannot remain planar

Anonymous

See 3

user228700

OK, what dyou mean by "because of the hydrogens"?

Anonymous

You see the hydrogens repelling ?

Anonymous

5:27 AM

because of lack of space?

Anonymous

See 3

user228700

Well, yeah, but this is the only way for them to be oriented that causes minimum repulsion b/w the hydrogens?

Anonymous

no thats why 2 is more preferable

Anonymous

non planar

Anonymous

loosing aromaticity

Anonymous

5:29 AM

losing

user228700

Riight, OK...

user228700

How is it possible to quickly observe and check if a molecule is planar or not?

user228700

@S007 Are u new to the chat? U can edit ur message within 3-5 mins.

Anonymous

you need to remember some exceptions

Anonymous

you cannot predict planarity

Anonymous

5:31 AM

no one can

Anonymous

its experimental

Anonymous

no i don't use the edit feature

user228700

Hm, OK...

Anonymous

saves time

user228700

Thank you. Are u gonna be around often? Usually, I have to wait for DHMO for my questions. (I don't have teachers)

Anonymous

5:32 AM

yeah

Anonymous

probably

Anonymous

im studying

Anonymous

but ill be around

user228700

Yeah, me too.

user228700

OK, cool. Shall I ping u for questions or no..?

Anonymous

5:33 AM

sure you can

user228700

OK, thanks :-)

user228700

6:16 AM

@S007: Does it help to know how to calculate the center of mass of uniform mass distributions to calculate electric field at a point due to various charge distributions?

user228700

I'm guessing...yes.

Anonymous

yes maybe...but we hardly use that when we can directly calculate electric field by integration

Anonymous

it boils down to integration

Anonymous

centre of charge you mean

Anonymous

mass doesnt play a role in electric field

user228700

6:17 AM

No, no!

Anonymous

?

user228700

U know how we use integration to calculate the COM of uniform mass distributions? We use a similar method to find the electric field at a point due to different charge distributions, right?

user228700

So, my question was, won't it be helpful to know how to do the former properly when doing the latter.

Anonymous

well, no. You do not need to know the former to understand the latter. COM and electrostatics can be studies as individual topics

Anonymous

all you need is integration

user228700

6:20 AM

No, I don't think u understand my question...

user228700

I'm talking only about the methods of integration used.

user228700

Not about the different concepts involved.

Anonymous

Yeah, the methods of integration are similar

user228700

Yeah, OK.

Bounty Hunter

8:09 AM

1

Q: Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics

I want to derive an expression for the internal energy of mixing, $\Delta_{mix}U$, and entropy of mixing, $\Delta_{mix}S$. The framework for this is the Lattice Theory of Ideal Solutions. Specifically, I am mixing $N_A$ molecules of type A with $N_B$ molecules of type B together. I am supposed to...

entropy statistical-mechanics

getafix

8:32 AM

@Kaumudi just an FYI about your question about integrations for charge distributions and COMs..when you integrate the infinitismal dV is not really an infinitesimal in the mathematical sense..even though the machinery of the integration remains the same

It's small, but big enough to average at microscopic fluctuations..

So it's small yet, "macroscopic" in some sense.. If that makes sense to you.. Lol if it doesn't just ignore it..

Think it's an interesting observation..thought I'd point it out

user228700

8:52 AM

It doesn't make sense, how "it's small yet, macroscopic" but that's OK at my level. Thanks for pointing this out :-)

getafix

Hmm like it's not as small as like a Planck length

Haha..say you have a sphere and you need to find the CM..when you integrate the density and volume element have sort of smoothed out the really really small inhomogeneties in the material

It's like an idealisation..anyway, I'm just ranting now

DHMO

9:30 AM

@Kaumudi heh

user228700

@DHMO :?

DHMO

@Kaumudi nothing. is there any question? as i have said before, when i am not here, you can just type out you question here (with a ping to me) and when i get back i can answer them.

user228700

No, nothing as of now, thanks :-)

user228700

(Sometimes, I can't move forward until Ik the answer si yeah, that's why I said that to S007)

orthocresol

11:19 AM

fun times, another nadine user, another nadine question

getafix

@orthocresol o/

orthocresol

I don't get why the guy is asking about those stat mech derivations with such complicated equations. :D

getafix

hahaha lol..yeah

btw..i never congratulated you..so

congratulations! you are a moderator now

haha

orthocresol

Thanks :)

getafix

btw..as a mod, what do toy recommend I do about my post..I asked about it a little while earlier..

orthocresol

11:29 AM

Bounty it, I suppose.

getafix

No not that one..

but yeah I plan to bounty it soon, maybe..

orthocresol

Heh, which one?

getafix

"Hey so guys..one of my answers earned a few down votes, don't know why.,if it is wrong, I'd like to fix it or delete it altogether because I don't want to spread misinformation
Since downvoters did not give a reason, I don't know if this is the case..i mean I thought I was right and which is why I posted it. So is it okay to delete posts for this reason?
The post in question is this one"
http://chemistry.stackexchange.com/questions/61443/significant-figures-in-ph-calculations-does-ph-0-30-count-as-2-or-3-significant

This one..

it got a few downvotes early on, but I don't know the reason behind it...If I am wrong, then I'd like to do something about..either fix my mistake or delete the post altogether..misinformation is bad imo. Would deletion be acceptable?

orthocresol

It's always fine to delete. However, I wouldn't be so quick to jump on one downvote being a sign of it being incorrect.

getafix

* 2 downvotes..if it had three, I would;ve done it and collected peer pressure haha ;)

Oohh that table looks nice..I should learn how to do that

orthocresol

11:33 AM

Or two for that matter. I didn't look into that question very much (not interested in sig figs), but if the mistake that Dave pointed out was corrected, then I wouldn't bother too much.

Especially since the downvotes were before that comment.

getafix

yeah that's true..what I am afraid is if i got some of the rules wrong, OP or someone else for that matter reads it and then gets his homework/exam question wrong

orthocresol

If you're afraid of it being wrong, then delete it, the score shouldn't really matter in that case. This morning I just deleted one of my answers sitting at +5 because it was far too simplistic.

getafix

yeah it's 16 rep points so meh..

orthocresol

Deletion doesn't affect reputation

30

Q: If I delete an answer, do I lose reputation?

If I delete my answer with some up votes, do I lose the reputation? Or, if I delete an answer with down votes, is negative reputation negated?

support reputation deleted-questions deleted-answers

getafix

I'll wait for a bit to see if someone points out something fundamentally wrong, or offers an answer that completely disagrees with it

oh wow okay..cool

did not know that

orthocresol

11:39 AM

Hmm, nope, wait

Think yours doesn't fit the criteria in the post.

getafix

is score of 3 or greater and...blah blah or score of 3 or greater or..blah blah

too lazy to type haha

orthocresol

yeah, hasn't been around for 60 days and isn't at +3

M.A.R.

Nadine

1

carbonyl-compounds organic-chemistry reaction-mechanism

For anyone interested, this is the new Nadine avatar.

CC @Mart

getafix

so it is either of the two conditions? or do i have to meet both?

meh anyway, should trawl for questions to answer..

M.A.R.

I get the creeping feeling that someone is out there downvoting every single post of mine. O.O

getafix

11:45 AM

haven't written a good answer in a while..

orthocresol

I believe it's either.

M.A.R.

Not just me, but any high rep.

getafix

:O @M.A.R.

Conspiracy!!

orthocresol

@M.A.R. You can always flag it for moderator attention.

M.A.R.

NWO

orthocresol

11:45 AM

But that doesn't mean I'll give you the attention.

getafix

A foul game is afoot

M.A.R.

@orthocresol Meh, I'm just being superstitious here

@orthocresol You're already giving me enough attention

orthocresol

I get downvotes very rarely. That answer that made it to meta was the only time in recent history.

getafix

yeah..i think yesterday was the first time i got a downvoe

and also the second haha

I had an "un"-upvote in the past

orthocresol

11:59 AM

@M.A.R. Do you have any idea how many Nadine accounts there are?

M.A.R.

@orthocresol nope

orthocresol

Well, there are 9 of them currently...

And it seems quite a few of them got deleted, so there's more on top of these...

I just wonder why he/she can't create a normal account.

M.A.R.

12:12 PM

It's a he. It's ALWAYS a he.

6 dumbest ideas politicians have about science

►

user228700

12:32 PM

@M.A.R. -__-

CowperKettle

are gene sequencing questions on-topic in the chat?

> In the second stage of analysis, degenerate primers are used to amplify a 400-nucleotide fragment of the gene, after which the this DNA fragment is sequenced from the same degenerate primers.

I'm not sure if this is possible

To sequence a DNA fragment .. attached to primers?

Maybe they meant "we sequenced the electrophoretic bands corresponding to the appropriate primer lengths"

Good evening all

getafix

@CowperKettle o/

I am guessing they should be fine, but I don't know much about it

CowperKettle

thanks!

> In the second stage of analysis, degenerate primers are used to amplify a 400-nucleotide fragment of the gene, after which the this DNA fragment (amplified using these degenerate primers) is sequenced.

I think this is more proper.

user228700

1:08 PM

Hi guys :-)

user228700

Could u help me to draw resonance structures for the following compound:

user228700

Basically, I'm trying to ascertain whether or not this ^ stricture is aromatic.

user228700

To do that, I must first check whether it is a conjugated system and whether it is planar.

user228700

To check if it is conjugated, I need to find out the hybridization of all the atoms in this compound; if it is anything with steric number less than 4, then I'm good to go, in that I can say that yes, this compound is definitely conjugated.

user228700

1:14 PM

But to find the hybridization of these different atoms, I need to make sure that I don't count any delocalized lone pairs.

user228700

And for that, I must draw the resonance structures.

user228700

Phew. So that's what I'm trying to do and I'm finding it difficult...

user228700

Please help?

DHMO

1:27 PM

@Kaumudi start with the resonance structure lol

assume that it is planar

N has 2 electrons, S has 2 electrons, only C has unpaired electrons...

user228700

Yeah...

DHMO

so i don't see any resonance structure, except if you make every atom charged

user228700

Oh, shit.

user228700

That structure is wrong by just a bit. The sulphur atom should have 2 lps.

DHMO

yes

i'm only talking about the p orbital

so of course there can be resonance

basically you can just transfer the double bond around the loop

(am i contradicting what i said earlier)

user228700

1:35 PM

Lemme try (again)...

user228700

I'm checking to see if any of the lone pairs can be delocalized...

user228700

And it's not working :/

user228700

If I do that, the nitrogen atom is forced to have a lone pair and two double bonds and since nitrogen can't expand its octet, it doesn't work...

DHMO

user228700

Huh?

user228700

1:39 PM

Hang on...

DHMO

@Kaumudi you know, just delocalize all the p orbitals...

user228700

Ur formal changes seem messed up... :/

DHMO

@Kaumudi where?

i hid hydrogen atoms

user228700

Second structure, Sulphur, how many lone pairs does it have..?

DHMO

two in the first structure

user228700

1:44 PM

Second structure..?

DHMO

one?

user228700

OK, can u pls explain how u went from the first structure to the second?

DHMO

I switched the double bond from there to there lol

user228700

Hm :/ Then how does that carbon actually have a negative charge? And where did the other lone pair on Sulphur go?

DHMO

user228700

1:50 PM

Ah, u didn't switch the double bond, exactly...u introduced one of sulphur's lone pairs into the ring.

DHMO

well...

user228700

It does make a difference, esp. since u didn't really show anything but the atoms IN the ring in ur first diagrams...

user228700

Anyway, OK, I'm trying to do this by myself, hang on...

DHMO

my fault

user228700

No problem :-) Actually, I must thank u for drawing these. But hang on, I'm trying...

user228700

1:54 PM

Hey, so after getting that negative charge on the carbon in the second structure, how did u decide what to do?

DHMO

as I said, I just switch the double bonds around the ring

user228700

I mean, we could've taken that charge and made a pi bond b/w that carbon and the adjacent nitrogen...but yeah, we can't do that, since nitrogen can't expand its octet...

DHMO

by "switch" I really mean that I use a different pair of atoms to have the double bond

@Kaumudi so you remove an electron from nitrogen before doing that

user228700

Yeah...

DHMO

i just switch the bond first

user228700

1:55 PM

I didn't consider going in the other direction, dammit.

DHMO

and assign the formal charges later

user228700

Hey, why is this wrong:

user228700

DHMO

@Kaumudi because you forgot a formal positive charge on the top nitrogen

user228700

It looks like the next thing u did was to have the double bond be b/w N and S, but I don't see why we've gotta break the other pi bond to have this happen...

DHMO

1:59 PM

@Kaumudi both are valid resonance structures...

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