The Periodic Table - 2015-11-01

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12:58 AM

@Jan Geez, that guy... how to avoid such stuff?

1:30 AM

@orthocresol Thanks for fixing one of the most embarrasing errors ever!

@Mithoron Ignoring and keeping calm ;)

1:50 AM

YES! I finally managed to give the most meta-answer possible!

0

A: Solid phase peptide synthesis (SPPS): why does capping after each coupling improve results?

if you cap then you “block” all of the peptides that you are synthesizing.(?) No, you don’t, the order of steps is important. First you try to couple your new amino acid to the solid phase. You will end up with uncoupled ends with free amino groups and coupled ends with a protected amino gro...

@Jan flagged for layman’s terminology

2:13 AM

Mods, please show up and shun the 'Guest'! D=

3 hours later…

5:37 AM

@Jan No problem :) I didn't bother running it by you since there's clearly no need to teach you how to balance equations haha

5 hours later…

11:05 AM

Hello

I would like to know

What is the charge of this ion: CN (cyanide)
appearantly it is -1
how can you know that?

ok found it!

C-N

4-5

= -1

11:20 AM

but this method appears to fail for

MnO4

still need some help...

to know the charge of this ion

12:03 PM

@privetDruzia How can we know that experimentally?  . . . or using qualitative methods?

@privetDruzia What exactly is this method?

Welcome to the Table BTW!

12:16 PM

@Ϻ.Λ.Ʀ. It appears to be some attempt to subtract the group valency of one atom from another.

@orthocresol But what's the logic behind it?

I thought the best we could get by guessing is drawing the Lewis structure.

@privetDruzia Short answer: You memorise it. Long answer: You memorise one million other facts about the Periodic Table, and by the time you know enough to deduce the charge on the ion, you will have seen the ion so many times that you will have memorised the charge.

Heh!

+1. This whole proposal is doomed to fail, since people rarely treat their answers like their children. — Ϻ.Λ.Ʀ. 1 min ago

@Ortho that answer is painful but right. I wouldn't have disagreed with the premise of the proposal that strongly, but it's true.

@Ϻ.Λ.Ʀ. There's no logic behind it. Yeah you could draw Lewis structures and try to fulfil the octet rule, and that would help you to a certain extent, for example with CN-. However it fails for any ion that displays hypervalency

@orthocresol Not octet. It's . . . complicated. (READ: I don't have the temperament to explain it.)

36

Q: Can I think of Algebra like this?

This year in Algebra we first got introduced to the concept of equations with variables. Our teacher is doing a great job of teaching us how to do them, except for one thing: He isn't telling us what we are actually doing when simplifying/solving for an equation. Instead of telling us we are ad...

algebra-precalculus

Bikeshedding math junk. (ノಠ益ಠ)ノ彡┻━┻

12:22 PM

Regarding the meta post, I think we need to decide first and foremost of the aims of any policy that is implemented.

Alright, I'm taking a nap. I only slept for 1:50 last night. :o

@orthocresol Flip the aims if the policy change won't do anything.

If we are not clear on what we want to achieve, then there is no way we can reach a consensus about how to do it. I mean, the second answer to the post already goes against the "don't give the full answer" idea that we have held.

Yes please get some sleep @Ϻ.Λ.Ʀ.

Look at the top comment: reddit.com/r/AskReddit/comments/3qymgl/…

@orthocresol Scratch we . . . I never saw this hint thingy on good thought out homework answers. Only the crappiest homework junk got hints as an answer.

Yeah, so there are two camps of thought, and I am sure there are merits to both sides. However we really need more input from others.

0

A: calculate the charge of an anion and cation

Elements like K, Li, Cs and Rb can only have +1 charge on them (Due to very high second ionization energy). Also, they can't have negative charge due to their low electron gain enthalpy (they are metals and are electropositive in nature). Also, Oxygen can only have -2 (in oxides, eg: H2O), -1 (in...

@Mart is it two month already? Should I post that 30k-char answer?

12:55 PM

Hi everyone

1:19 PM

hello

1 hour later…

2:25 PM

Flag please:

-1

A: Lifetime of a (reversible) hydrogen fuel cell system

pizza i dont know but it should last around 2 year to 6 years

Hi. I need some help (again) with some o-chem

Hullo @getafix

Hi @orthocresol

Always my rescuer..haha

I just happen to be extremely busy right now with my procrastination project.

oh i see.

2:35 PM

After six more years, I'll graduate with a PhD in International Relations

I had to take a break from mine

hahaha

My thesis will be on the diplomatic ties of the Procrasti Nation.

2

OMG! So punny..

Anyway, a side effect of studying that is that I learn about the Nations of Chlori, Bromi, Iodi, Hydroge, and Sulfo.

So what is it about org chem?

so i had the question about enantiomeric excess calculation, normally
e.e = [α]mix/[α]pure*100. So for instance if i were give [α]p = 24, and [α]m = +8 and am asked to calculate e.e and %age of R and S forms..I just 8/24*100 = 33.33% = e.e
the rest 66.6% is optically inactive, so the so the (+) form is 66.6% and the other is 33.33%.

But then what if there is more than one stereocenter, and the two stereoisomers in the mixture have different values of their specific rotations in the pure form..

the same approach doesn't hold, i have a feeling..this wasn't discussed in my class..

like a question like this: (-)-menthol ([a]D = -51) and (+)-neomenthol ([a]D = -21) The menthol – neomenthol mixture in a natural sample of mentha oil exhibits
[a]D = -33. What are the percentages of menthol and neomenthol in this oil?

So I was thinking if i do something like

[a]neo*(%age neo)+ [a]men*(%age menthol) = -33

and the sum of the 2 %ages = 100

2:50 PM

I think that makes a lot of sense

and solve...would that give me the right result?

Oh really? Okay. I was a little bit unsure..because what if it is a 3 component mixture?

Then it seems like you get two equations in three unknowns.

the linear system then admits a set of solutions...so...

i don't get it..then there may not be a unique solution. so can we not solve questions like that with more information?

So it is impossible to specify a unique set of percentages that gives rise to the observed optical rotation.

Yeah, probably not.

ah okay. Thanks.

I was just sitting here scratching my head..

2 hours later…

4:47 PM

33

Q: In Back to the Future, how did Marty get the timing right with the lightning strike?

So, in the first movie, presumably the Doc and Marty know exactly when the lightning will strike the clock tower. This is because Marty has the flyer with the picture of the stopped clock on it. In order to power the DeLorean, the Doc cooks up this contraption to conduct the lightning through a h...

back-to-the-future

@Mart-y how did you?

5:00 PM

Hey seal.

Hullo

Oh. You're learning.

`(.•.)´

What do you mean?

That "hello" is inferior.

How about "hallo"?

5:02 PM

Fake "hullo".

Salutations, @Ϻ.Λ.Ʀ.

Nerdy, but not cool.

01101000 01100101 01101100 01101100 01101111

Unless you're a linguist.

'Allo 'Allo!

5:03 PM

@orthocresol This could work.

@Mithoron Too French.

:D

I am wondering why the orthogonal wavefunction question got so many upvotes

room topic changed to The Periodic Table: Haikus are awesome / Chemistry is even better / So pull up a chair ||| Want to turn MathJaX on? Try meta.chemistry.stackexchange.com/q/89/7448. For further LaTeX/MathJax assistance, visit this chatroom: chat.stackexchange.com/rooms/27198/latex-mathjax-help [blowing-the-lab-up] [german-stuff] [hullo] [love-you-all] [martin] [table-flipping] [tre] [welcome]

Haven't seen that kind of question score for a long time

Which kind?

5:06 PM

It's at +9 now

Who?

9

Q: Orthogonal Wavefunctions

My current understanding of orthogonal wavefunctions is: two wavefunctions that are perpendicular to each other and must satisfy the following equation: $$\int\psi_1\, \psi_2\, \mathrm{d}\tau =0$$ From this, it implies that orthogonality is a relationship between 2 wavefunctions and a single wa...

quantum-chemistry terminology

Ahh. mathematical-chemistry

It's not that I'm complaining, I was just a little surprised

0

A: How do you calculate a unit cell's dimensions from an XRD spectra?

There are two basic techniques. Single crystal You have a single crystal for which you know the orientation. The energies that satisfy Bragg's law change with the orientation of the crystal to the beam. This principle is used in WDXRF to make the goniometer. Powder diffraction The sample is ...

Above is NAA, I believe.

Gee, until we get to teach them the rules I'm gonna grow white beard.

5:12 PM

Amount of homework is terrible lately.

Yes, that's the price to pay for higher traffic.

The only thing we can do @Mith is not to hesitate on downvoting, not answering and closing them.

What do you think should be done then with HW questions?

Answer immediately?

No, answer like Ben does.

I mean for the "decent" types of HW questions

@orthocresol Oh? Answering completely is what I've observed 99 percent of the time.

5:14 PM

@Ϻ.Λ.Ʀ. For the rubbish questions? Or the decent ones?

@orthocresol Downvote and close rubbish. Answer in full the good ones. There shouldn't be any encouragement for hints.

See Ben's answer to that one.

@Ϻ.Λ.Ʀ. I see.

Scratches head I thought Ben answered that.

Oh wait. This one:

-5

Q: The most common elements in functional group

My question is what are the most two common elements in functional groups?

organic-chemistry

Part of what I wanted to bring up last time was, we need some canonical answers to a list of commonly-seen homework questions. So that new ones can be immediately closed as duplicates. I think we are probably in agreement about that.

We definitely are in agreement about that.

5:19 PM

I read Anders' comment: "The greater good here is to have a vast collection of chemistry questions with great answers, and if individuals don't get the full benefit of working out the answers themselves, is that something Chemistry SE should care about?"

We partially do care about that.

We don't want to attract idiots.

Well, I am speaking as someone with teaching experience.

I'm speaking as someone with meta experience. :P

I would never just give an answer to someone who asks a question, without at least discussing the question with them.

Yes, I respect the fact that this is of course not a classroom

@orthocresol Define "discuss".

5:22 PM

Basically what I do in homework questions.

@orthocresol It's a library. The analogy doesn't always work but in the case of treating questions and their comments it works good.

@orthocresol But long comment chains are a problem. I engaged in one or two of them and they tend to hide valuable piece of info which should be in the answer or the post.

@Ϻ.Λ.Ʀ. I agree, and I am very guilty of not following up comment discussions with proper answers.

@orthocresol Yeah . . . Usually after the conference no one comes up to write an answer.

Half of the reason is because typing out proper answers takes time and I do not always have that luxury, and the other half of the reason is entirely my fault, it's because I feel that the student has gotten what they want so there's no need for further action on my part.

Well, I think I am digressing a bit.

My opinion is just that we shouldn't just give perfect answers to HW questions immediately, solely for the benefit of the asker.

chemistry.stackexchange.com/questions/40043/… -- Possible help vampire @Mith @Ortho, don't engage further.

5:27 PM

TBH, I have a extremely time consuming idea.

@orthocresol Yes, I'm a student and I know how fun and awesome and great it is to reach the final solution step by step. But thing is, people don't come back for their answer after a couple of days.

We don't have to wait $x$ days before doing anything. We can always try to help via comments. The answer will just have to wait until either 1) they understand it; or 2) $x$ days have passed.

@Ϻ.Λ.Ʀ. And here I thought the guy isn't that bad...

My extremely time consuming idea is: I can write up a long list of typically seen HW questions, and you guys (or I) can answer them, and then we have all the answers we need to flag new HW questions as duplicates.

@orthocresol No no, as I said, long comment chains hide some important and valuable chunk of info.

@orthocresol How will you know that they understood it if they don't reply to you?

5:33 PM

@Ϻ.Λ.Ʀ. Yes, which is why we should edit the question appropriately and answer them after whatever needs to be clarified is clarified. If they don't reply, just wait $x$ days, or close it if it is a lousy question.

@orthocresol (งಥᴥಥ)ง︵sʎɐp $x$ ʇᴉɐʍ ʇsnɾ

@Ortho what percent of the active voters, editors, answerers, commenters etc. come back to a question after several days?

Yeah, TRE or bumping or something else sometimes gets the question some attention, but that's usually too late.

@Mithoron He could be a genuine asker, but help vampire is someone who seems to have hidden their real questions, and this seems to be the case here.

BTW @Mith @Ortho pro tip: Whenever you're asking for effort/clarification, add "please do so by [edit]ing your post".

That [edit] is magix.

That goes for all commenters. ^ \CC @Jan @Wild @Todd @Others

Hmm, 100 CV's left to the mighty ron.

After that, I'll be the top CV reviewer. ᕙ(⇀‸↼‶)ᕗ ᕙ(⇀‸↼‶)ᕗ

bye guys o/

Guy buys \o

5:49 PM

@Ϻ.Λ.Ʀ. I see where you're coming from. But I need to grab dinner first.

@orthocresol Grab dinner first. Hmm, does that mean you will be attacked by an electrophile?

My opinion is that posting a complete answer immediately is only minimally more helpful to the asker than posting a complete answer 2 days later.

However, it does inconvenience the answerers substantially, unless someone has a way to keep track of all homework questions that are 2 or more days older.

What'd you think of my time-consuming proposal?

Should I call you salicylic acid after dinner?

@orthocresol The point isn't about immediate full answers being helpful or not, it's about the fact that your proposal won't work.

A small fraction of users read meta policies, a smaller fraction obey all the time.

It will turn into another "hint" policy. One that no one abides by.

Fair enough.

But yes, I agree that step-by-step, gradual answer processing is way more beneficial.

5:53 PM

I think I will write a separate proposal in an answer later.

I need to develop my idea a bit

I think I will go and propose that hint thingy be removed.

Sure, I am all in favour of that

Nobody follows it and providing a hint as an answer is stupid (as Normal Human wrote)

Hint: You're an organic molecule.

Keith Whittingham

1

ionization-energy

Look at that avatar . . .

I've never seen any hint answers, but they should be flagged as NAA.

orthocresol, Oxford, United Kingdom

2.6k 4 22

thermodynamics homework organic-chemistry physical-chemistry stoichiometry inorganic-chemistry acid-base

Look at that avatar!

`(.•.)´

5:57 PM

:)

okay, I am a bit busy tonight, so maybe I will pop back into chat later

(:

Will you be present this TRE?

I may be late. But I should be back by 5pm.

\o chips

@orthocresol K.

Copper then.

Copper = Cu = C u = see you.

Copper!

@orthocresol Yeah, I've figured anything chemistry that you don't understand in normal talk is a reference to its chemical notation.

6:06 PM

@orthocresol It doesn’t fail if you treat hyperconjugation properly imho. But it's always simpler to deduce the bonding situation from knowing the charge than vice-versa.

6:52 PM

@Ϻ.Λ.Ʀ. maybe we should make a chemistry language! Copper means bye (see you), K obviously means ok, anything else to add?

@TanMath CuTe

@Ϻ.Λ.Ʀ. hehe..

wait .. HeHe!

like helium!

7:12 PM

HeLiUM

I Am MAr

ThIS + IS -> FUN

I DsAgRe.

I DISAgRe TOO

HeY + YOU

@ORtHo CReSOl

@Jan your name isn't elementic! (ಠ益ಠ)

It's just easier to say CH3C6H4OH :D

An can be used as a general symbol for the actinides.

@orthocresol And J?

But J doesn't appear on the Periodic Table.

7:25 PM

Yah.

I don't know why people are so excited about having weird names for the transactinide elements

There are still so many one-letter symbols that aren't used!

:p

Although, if you think about it, even if they are given one-letter symbols, I doubt we will ever use them anyway...

I'm the general formula for a metal argonide (?). Therefore, I don't exist.

@MArTiN is something even weirder. MAr 3+ and TiN 3-, I suppose.

2

@Ϻ.Λ.Ʀ. You're relative atomic mass backwards.

Mass atomic relative.

7:29 PM

BTW @Methylphenyl alcohol are you still busy being busy?

@orthocresol Or Read Access Memory, if you put it that way.

@Ϻ.Λ.Ʀ. Indeed I am, I was just drawn back to chat by @Jan's message, which I absolutely forgot to reply to

Great.

I guess the question then becomes how do you treat hyperconjugation at the level that OP was asking

#Typical_Procrastinanian

I don't know :P

7:31 PM

Haha xD

I shall go back to being busy

Please do not ping me

The Periodic Table acts like a methamphetamine. You get drawn to it after the first use, and you have to get more and more of it every time.

@orthocresol OK.

@orthocresol But . . .

@orthocresol Whatever.

@orthocresol OK.

0

Q: Solubility of mass solute

If 202grams of kNO3 is dissolved in 100cm of water at 4 degree celcuis, what mass of the solute will remain undessolved?

Yawns

@ortho @seal why ever not? @o-Me-C6H4-OH!

@Jan The "ortho" o should be slanted.

I know @Ϻ.Λ.Ʀ.

7:39 PM

I know you know.

It wasn't a tutorial, but a reminder. :)

7:51 PM

Boo for the automatic and non-manual bounty awarding on this question:

7

Q: How exactly does the reaction between alkyl halides and silver nitrite occur?

$$\ce{R-X + AgNO_2 -> RNO_2}$$ Now depending on the $\ce{R}$ and solvent the reaction can occur via $\mathrm{S_N1}$ or $\mathrm{S_N2}$. When the reaction proceeds via $\mathrm{S_N1}$ the product formed is $\ce{R-O-N=O}$ whereas for $\mathrm{S_N2}$ it is $\ce{R-NO_2}$. Why is this so? According to...

organic-chemistry reaction-mechanism halides

Two contradicting answers, one long and thorough and backed with references, the other earlier and bounty-awarded D=

:-(

similar here: chemistry.stackexchange.com/questions/37257/…

The (earlier) clearly wrong answer has more upvotes than the (later) correct one.

@Loong Lemme balance the votes.

and now I should read @Jan's answer

8:31 PM

@Loong Meaning you should find the typos and edit them out ;)

@Jan looks quite fine

Celebration: I wrote an answer and @Loong found no typos! Now that sounds like a first! \o/

OMG

@Mithoron That is an unhelpful edit D=

What edit? Looking

8:36 PM

Lol@Loong that was a ratio.

> nitromethane : methyl nitrate

@Jan yes, yes, I can see that

@Jan Which edit?

@Ϻ.Λ.Ʀ. Adding HSAB to the post.

Also guys:

The Hanson Brothers - The Hockey Song

@Jan To which post? Or do you mean post office?

I don't see the edit. O.o

The silver nitrite question.

8:44 PM

Oh wait. It's a suggested edit.

I thought @Mith got to 2k already.

12

Q: Natural Bond Orbital (NBO) analyses: Physical significance/interpretation of E(2) 'stabilization energy'?

PREFACE: I am no expert on this topic. My questions at the bottom may be off base. I have some experience with symmetry-adapted perturbation theory (SAPT) when it comes to analyzing intermolecular interactions. The total interaction energy of a system can be quantified in four different energy...

computational-chemistry theoretical-chemistry orbitals intermolecular-forces

@Wild kitty you were on a rep diet?

@orthocresol we might need about 60 000 NAA flags: math.stackexchange.com/…

Hehehe!

@Ϻ.Λ.Ʀ. @Wild kitty wanted a shiny badge ;)

@Jan More like rusty.

Pff, you clearly don't value badges enough. I hereby take away your marshal and pin it to my own chest. =*,...,*= Shiny golden badgy =*,...,*=

8:55 PM

Jun 24 at 19:51, by santiago

jealous?

@Ϻ.Λ.Ʀ. I knew you would do that.

I knew I would do that too.

Hmm, @Ortho did you get to meet Santiago?

@Loong Ouch. Well, it's up to us to decide whether we want chem.SE to be like that.

@Ϻ.Λ.Ʀ. I saw the stuff he did on the site, although I don't think I actually talked to him.

@orthocresol Hint: The answer is not "no".

@orthocresol Hint: He did a lot.

@Ϻ.Λ.Ʀ. Naturally.

8:58 PM

@Jan (/¯◡ ‿ ◡)/¯ ~ ┻━┻

Alrighty, I turn off the lights for the night. G'night people!

Does the biochemistry definition of standard state not include temperature?

Let me look it up. I'm 95% sure it doesn't, but I just want to be sure

Goodnight @Ϻ.Λ.Ʀ.

@orthocresol The definition of standard state does not include temperature.

@Jan Yes, but the definition of standard state also has unit activity of $\ce{H+}$.

@orthocresol according to the Green Book, only the concentration of H+ is different

@orthocresol Yes, and the only thing that changes for the biological definition is that the activity of $\ce{H+}$ is defined as $10^{-7}$

9:07 PM

@Jan @Loong Yeah, that's right.

Hmm, I checked a biochem textbook and it says to use $K'_\mathrm{eq}$ too.

(I love agreeing with @Loong, it means I must be right xD)

9:24 PM

1

Q: Influence of neighboring fluorine and hydroxyl on carbocation

Which out of 2-fluorobutane-3-yl carbocation and butan-2-ol-3-yl will be more stable? I agree that fluorine has greater inductive effect, but what about resonance effect of those?

stability carbocation

Hey, I thought about answering this :(

@Mithoron I voted to close pre-edit where the question was much worse. Let me consider voting to reopen.

I'll add a diagram

Hmm, but there's a problem - these cations don't really exist

Why, would they form the epoxide or halonium immediately?

It looks like

Creation with anchimeric assistance would mean they would be oxonium/fluoronium from beginning.

9:35 PM

Well, mentioning that would make the answer even better I suppose :D

How sly to put it in the reopen queue like that ;)

Does my edit automatically put it in the reopen queue?

It should.

All edits to closed questions should.

Ah, I see.

chemistry.stackexchange.com/help/reopen-questions

> Closed questions that receive edits within the first 5 days of closure are automatically put into a review queue to be considered for reopening.

9:54 PM

chemistry.stackexchange.com/review/reopen/27330

Just voted =3

2 hours later…

11:47 PM

Come on, Chem.SE! 43 rep points in 13 minutes, can you do that? Second mortarboard day? =D Go go go! Faito!

11:59 PM

0

A: When is it safe to answer homework questions?

Proposal I feel that we should also touch our original homework question guidelines and modify them. All my proposed additions are bolded, proposed deletions are stiked through, stuff in brackets is meant as my comments unless otherwise indicated. Watch out for answers that provide a full...

Just so it is here and @Ϻ.Λ.Ʀ. isn’t the only one to see it, because he always hogs meta ;)

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Transcript for

Nov '151

The Periodic Table

Haikus are awesome / Chemistry's even better / So pull up a chair

blowing-the-lab-up german-stuff hullo love-you-all martin table-flipping tre welcome

join this room
about this room

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