@orthocresol sleeping usage and credit card patterns?

You will never find out about my supersecret credit card no one knows about

@M.A.R. I would rather just ignore them and leave them to their own devices

can confirm that Brian is the opposite of evil IRL

I think...

@pentavalentcarbon so we just have to wait until he reveals his doomsday plan

I don't think he has one, he's too preoccupied with his daily chores

What if the ultimate result of him vacuuming his house is creating a black hole?

then none of us shall be the wiser

@pentavalentcarbon superwiser?

I fear I shall lose this dad war

You already did. I'm not even a dad yet

You think I'm a dad?

Since you're pentavalent, maybe you're a mom

?!?!?!

I'm so lost

Or maybe a gun clip with five ammos

@pentavalentcarbon is there internet in the jungles of Amazon?

Maybe you're in Jumanji

No I'm in Pittsburgh

Pittsburgh, Jumanji?

it's a bit too cold for that

@pentavalentcarbon I was getting somewhere with that joke, but I got lost myself

@pentavalentcarbon Arctic Jumanji then

getting closer to the same page

Random question:

Does water of crystalisation contribute to the resulting solution volume when a hydrate dissolves in water?

@Secret I would guess the answer is no; say one molecule of the compound has X molecules of water of crystallization; then, the extra volume due to those X H2O is = X * (18/NA) cm^3 which is extremely insignificant unless X is at least of the order 10^15, which rarely happens anyway

Any chemsketch pros?

mind having a look at why my wedge bonds are not smooth?

first time user here I wonder if you've seen something similar before. thanks ^_^

Single atom of strontium suspended in a magnetic field

@GaurangTandon [Re: Why does nitrogen have a maximum covalency of 4?] The general problem with covalency is, that there is no good and unambiguous, or even official definition of it. Some use the number of shared electron pairs, some use the number of covalently bound substituents (although how would you tell what is covalently bound?), and there are probably more uses out there.

Valency is not the same as covavalency, but it suffers from the same fuzzy definition problem...

The IUPAC defines it as the number of univalent atoms. That makes it a fixed number: Nitrogen 3, carbon 4, halogens 7, Xe 8, He 0, etc... Greenwood waters the definition down to binary hydride or twice the number of oxygen atoms in its oxide(s). This means it can have more than one value. Which one do you take? Which one is correct? It depends.

More rigorous is coordination number. It is something you can actually count, and it only depends on the compound you are looking at. Therefore hypercoordinate compounds have a cn higher than usually expected. Besides that valency and related concepts are not useful, they actually don't tell you anything. Maybe they may help you classify what is "normal" or "boring", but when it comes to actual chemistry, it doesn't tell you anything.

I understand that for some fundamental, basic beginners course, these simple concepts can be helpful at getting a grip. However, it really is necessary to teach from the beginning, that there are limitations to this point of view, and maybe hint at the deeper going stuff. It really is hard to fight these common misconceptions, because some teachers don't know better, and some students only trust what their teacher says.

The d-orbital contribution and octet-expansion are such problems, and I am not yet prepared to give up the fight.

\o @Hippalectryon

@Martin-マーチン I am not trying to fight though ^_^

@Martin-マーチン I agree with that. I myself searched for the definition of covalency before posting the answer, but I couldn't find anything conclusive

@Martin-マーチン "when it comes to actual chemistry, it doesn't tell you anything." Yes, I agree with that also. I myself am more used to the oxidation state (is it more/less useful than coordination number?), that's the first thing I commented on the question of the OP as well, but later figured out he was asking for the covalency instead

@Martin-マーチン come to my region high schools once, you'll be amazed at the quality of the high school chemistry textbooks (spoiler: they're terrible :P). I myself am grateful to the quality answers out on Chem.SE otherwise I would have never learnt any chemistry at all

so, what do you think I should do? edit the answer to include all the details you mentioned?

oxidation state is quite well defined, but there are also a few problems. usually it is safe to use. Know what you're doing and everything will be swell. For example, you need to know the structure (and coordination number) to assign oxidation numbers in N2O5... Problematic are cases like Fe3O4... and fractional on in general ;)

@Martin-マーチン yes that's reasonable

@GaurangTandon Well I found that initial one quite compelling, that's when I edited it and voted on it chemistry.stackexchange.com/revisions/90576/3 Maybe add that you define covalency as number of shared electron pairs to make that point clearer, but nothing more was asked and the hypercoordination stuff will probably just confuse op

:q

ups... wrong window

fine editing that

check now chemistry.stackexchange.com/questions/90573/…

is it ok?

@GaurangTandon It certainly is better, but has phosphorous really covalency 5 in PCl5? There are only 8 shared electrons. The bonds itself have high ionic character (at least more than in PCl3), so is it really correct assigning a covalency in this case? In the first case -- using covalency = no of shared electron pairs -- the covalency would still be 4.

And i would say that the coordination number is an older concept than valency/covalency

@Martin-マーチン whoops fixing

@Martin-マーチン "There are only 8 shared electrons" whoa, then how come there are five sigma bonds with chlorine? is that because of this 4c-3e thingy? chemistry.stackexchange.com/a/18544/5026

*3c-4e

@GaurangTandon yes and no. What ron presented there is an approximation, too, but it will help you understand why there are only 4 ep shared, the non-bonding orbitals don't contribute to that.

in a MO set-up you'd get the same conclusions from symmetry adapted ligand orbitals.

basically you have one totally bonding orbital s of P with ligand lone pairs, two degenerate orbitals using the equatorial ligands, and one orbital using the axial ligands; and of course the anti-bonding combinations

honestly I didn't get a thing of what you said, don't know MO theory yet, I'll edit my answer accordingly though

wait

how's it now? chemistry.stackexchange.com/a/90576/5026

yes, that very swell

:D

@GaurangTandon They aren't bad . That's just something everybody going to coaching centres keeps on repeating . I don't know why, Nearly all the jee toppers say that NCERT is a must.

I don't use NCERT though

@Martin-マーチン your oxidation number is +3 when you react with me, -1 with everyone else, and -5 when sending a mod message to someone you suspended

You're pretty much nitrogen

I blame you for ammonia

What is wrong with you?

Hmm, ammonia is sometimes useful though

i've never been -5 then...

Oh hey alive person

oh nitrogen as -5 that's gonna be unstable

@Martin-マーチン aren't you when suspending someone?

Or you're the cold blooded killer type?

I'm not suspending people.

That always is a mod-consensus

we work in harmony here

@AvatarShiny I personally dislike NCERT; though it's preface mentions the top professors wrote it, I still find it lacking minute details that are useful for JEE, and the presentation of the content is bleak

NCERT has some of the worst misinformation available on the internet

@Martin-マーチン not the only one here, but certainly the most popular

yes it is...

the only thing that's good with it it's available for free online, digitally

unlike the other highly priced books

@GaurangTandon All books are ** cough** free ** cough ** if you know where to find them.

@AvatarShiny ;) i was unlucky though, bought all my books genuine :(

Rich kid

Nope, though I wish I was

no, i live in the poorer side of lko

you where?

Delhi

cool

My grandparents live in lko

Oh

When I write "atm" (atmospheric pressure) or "M" (molarity) in mathjax, is it necessary for \mathrm to hug them?

earlier I used to let them be the way they are, but the \mathrm form looks better

though it makes my post more tedious to write

<pings_mathjax_superusers>

hmmm... NCERT might be free in India, it is not available here though...

@GaurangTandon $\pu{1.23 atm}$, or $\pu{1.23 kJ//mol}$, or $\pu{1.23 kcal mol^-1}$

pu = physical unit; part of mhchem

@GaurangTandon also note that correct: \ce{Cu^2+} not correct \ce{Cu^{2+}} ref: chemistry.stackexchange.com/review/suggested-edits/73035

@Martin-マーチン never knew that was easy :P

@Martin-マーチン good to know that, was already growing tired of mathrm

play.google.com/store/apps/…

they even have an app on ios, android, windows phone

dunno if it's region locked though

i can see that at least... the content might be locked though

does this site work?

ncert.nic.in/textbook/textbook.htm

select "Class XII" in the first dropdown

then chemistry

then part I or II

that should give you a per pdf view of chapters

as well as an option to download the complete book

oh yeah, that works...

they also have another link to download the epub version but it is currently down epathshala.nic.in

probably a lot of CBSE students are simultaneously prepping for upcoming exams xD

hmmm... 2007, and they had to be bought previously...

yeah but 170+170=340 (2 parts ncert) for a chem book in class XII rupees is way cheaper than other chem books in my region

The one I currently using cost 900, and it's only slightly better

denomination in INR indian currency

nonetheless it's absurdly high for a ten year old book

sure, I understand, and one can appreciate the efforts to get affordable education to the people.... if it were not for the many mistakes...

however, the worst is when students insist that only what is given in these books is true, everything else must be wrong...

definitely that's the worst

@GaurangTandon Nice source, thank you. That might help us understand better some of the problems of our users.

@Loong welcome :) i wonder quite a lot of users refer to the NCERT here

Oh, and while we're at it, do note that there's a difference between NCERT and NCERT Exemplar books.

I used this non-official source for NCERT exemplar tiwariacademy.com

tl;dr: NCERT = main syllabus book prescribed for all students; has theory+review exercises; NCERT exemplar = supplementary book containing slightly tougher problems, no theory

What is given wrong in NCERT? @GaurangTandon

quora.com/What-are-some-blunders-in-NCERT-textbooks

^ blunders in NCERT

@Rick apart from that link, two more facts: (1) weak presentation of content (2) no updates since 2007 (10 years!)

@AvatarShiny well yeah I knew biology had alot of mistakes and I really hate that even NCERT says that glass flows..but is there anything else gravely wrong?

and as I said already, I haven't used NCERT much, but i haven't heard as good about from anyone, at least not as much as it's expected to be

Exemplar questions are decent though

@Rick I'm pro NCERT

I haven't used it though , pretty good for CBSE

@AvatarShiny Yup, even I like NCERT

@Martin-マーチン just tried it, it works like magic! :D now I realize I've been doing it wrong all along; I wish it was taught earlier :(

@Martin-マーチン Although NCERT has many mistakes, most of the examinations in India are based on it. So, students have no choice but to learn and 'memorize' NCERT. And most of the students have no interest in obtaining correct information but only score high.

@Martin-マーチン ugh

eating harmony

@ApoorvPotnis so you're saying why experts in a field don't use a convention experts in another field use? Well, I'm afraid the answer would be they just don't.