[seqfan] Re: Chemistry sequence

[David Wilson]

----- Original Message ----- 
From: "Richard Mathar" <mathar at strw.leidenuniv.nl>
To: <seqfan at seqfan.eu>
Sent: Friday, August 28, 2009 11:10 AM
Subject: [seqfan] Re: Chemistry sequence


>
> http://list.seqfan.eu/pipermail/seqfan/2009-August/002237.html
>
> dw> How many molecules have total atomic number n?
> dw>
> dw> There are clearly issues with this question, such as counting
> dw> low-temperature helium compounds. Another problem arises from trying 
> to
> dw> count, say, all the molecular configurations that could be formed 
> from,
> dw> say, 10 carbon atoms. Still, I wonder how far we could go with any
> dw> degree of confidence.
>
> To answer such a question, one would be forced to fix a definition:
>
> What is a molecule?
> Does this refer to some sort of stability of the compound at some 
> temperature?

> Do we count all different ionized forms individually?

> It there a cut with respect to the semi-stable isotopes/isotopomers that 
> may be
> employed (see in particular A007656 on which follow-up issues arise)?
> Would for example matter-antimatter states (nowadays created in collider
> experiments at least in the form of anti-Hydrogen) already qualify as
> individual candidates? Is TNT stable? Is the proton stable? would Tritium
> be admitted or Deuterium? More generally, do we count baryonic excited 
> states
> (or, beware, those with quarks not just of the up-down variety) of the
> nucleus(i)?

Protium, deuterium, and tritium all have the same atomic number, no?
So really, I'm talking about molecules with the same number of protons.
For starters, we can stay away from the ions and isotopes and consider
proton count as the atomic equivalence relation.

Yes, I realize that some molecules are stable with some isotopes of an 
element
and unstable with others, e.g, you'll die if you drink only heavy water. So 
for
argument's sake, if a molecule is stable with any isotope at any 
temperature,
we'll count it.

We can safely ignore antimatter, don't you think?

> Is a solid with cracks in it also a "large" molecule if it has a finite 
> edge
> length? (That is: where is the transition from a gaseous molecule to the
> liquid?) Is a cluster of 11 Gold atoms or are these Buckminsterfullerens
> molecules? Do we count them differently if they form a cage around some
> big other atom or ion?

I doubt we'll run into these problems for molecules of, say, 10 protons or 
fewer.
I guess I'm curious as to what the problems are at the small-molecule end.

> Is the DNA a molecule and how many cloned versions of these may exist in 
> real
> (and future) life forms on this planet, laboratory glass tubes and 
> elsewhere,
> in the frozen ice on Mars?

How many protons in the simplest DNA molecule? Probably more than we
will ever reach.

> Richard