Is hydroastatic acid possible?
Protoman
hydroiodic acid?
Madalch
> Is hydroastatic acid possible? Is it a even stronger acid than
> hydroiodic acid?
It might readily decompose to hydrogen and astatine, otherwise yes, it
should be stronger than hydroiodic. However, with a half-life of
eight hours (IIRC), very few people would bother trying to work with
it.
Peter Fairbrother
Hydrogen astatide is regularly synthesised. Yes it forms hydroastatic
acid, which is a stronger acid than HI - but the astatide ion tends to
become oxidised easily, and it doesn't always behave as HI does.
The simple chemistry of At has been explored and many results are known,
if a bit obscure.
20 or more interhalogens, CAt4, alkali salts - mostly used as
radioactive tracers - spring to mind, but some very complex
organo-astatine compounds have been made for nuclear medical research,
including heterocycles and even monoclonal antibodies.
Michael Moroney
>Hydrogen astatide is regularly synthesised. Yes it forms hydroastatic
>acid, which is a stronger acid than HI - but the astatide ion tends to
>become oxidised easily, and it doesn't always behave as HI does.
Wouldn't HAt be a weaker acid than HI due to At being less electronegative
than I?
How much does known At chemistry differ from I, other than HAt being a
stronger acid than HI and At- being more easily oxidized? From what
little I've read, At chemistry is very similar to I.
Madalch
wrote:
> Wouldn't HAt be a weaker acid than HI due to At being less electronegative
> than I?
No- the size of the halogen is more important than the
electronegativity. That's why HF is so much weaker than HCl, and HBr
is stronger than HCl, and HI stronger still. Similarly, H2Te is much
more acidic than H2S, which is more acidic than water.
Peter Fairbrother
> Peter Fairbrother <zenad...@zen.co.uk> writes:
>
>
>> Hydrogen astatide is regularly synthesised. Yes it forms hydroastatic
>> acid, which is a stronger acid than HI - but the astatide ion tends to
>> become oxidised easily, and it doesn't always behave as HI does.
>
> Wouldn't HAt be a weaker acid than HI due to At being less electronegative
> than I?
Size *is* important. :)
>
> How much does known At chemistry differ from I, other than HAt being a
> stronger acid than HI and At- being more easily oxidized? From what
> little I've read, At chemistry is very similar to I.
They are similar, except most noticeably in that inorganic astatides are
more easily oxidised than iodides.
For example, IIRC in cold 0.1M nitric acid oxidisation (to AtO-) is
almost complete for At-, and almost insignificant for I-. Don't take
that figure as gospel, but it's something along those lines.
It's nothing surprising - the trend is there going down the halogens. It
does have some minor consequences for the synthesis of organic
astatides, but I don't know that much about it.
Please don't get the impression I'm an At chemist; I just read some
books about it a long time ago, and have skimmed a few abstracts since!
-- Peter Fairbrother
Andrew Usher
> Hydrogen astatide is regularly synthesised. Yes it forms hydroastatic
> acid, which is a stronger acid than HI - but the astatide ion tends to
> become oxidised easily, and it doesn't always behave as HI does.
>
> The simple chemistry of At has been explored and many results are known,
> if a bit obscure.
>
> 20 or more interhalogens, CAt4, alkali salts - mostly used as
> radioactive tracers - spring to mind, but some very complex
> organo-astatine compounds have been made for nuclear medical research,
> including heterocycles and even monoclonal antibodies.
Where can I read anything about this? I've never heard of its
being investigated like this.
If At has had this much work done on it, why hasn't radon, which
is more accessible and at least as theoretically interesting?
Andrew Usher
Peter Fairbrother
> On Sep 18, 2:34 am, Peter Fairbrother <zenadsl6...@zen.co.uk> wrote:
>
>> Hydrogen astatide is regularly synthesised. Yes it forms hydroastatic
>> acid, which is a stronger acid than HI - but the astatide ion tends to
>> become oxidised easily, and it doesn't always behave as HI does.
>>
>> The simple chemistry of At has been explored and many results are known,
>> if a bit obscure.
>>
>> 20 or more interhalogens, CAt4, alkali salts - mostly used as
>> radioactive tracers - spring to mind, but some very complex
>> organo-astatine compounds have been made for nuclear medical research,
>> including heterocycles and even monoclonal antibodies.
>
> Where can I read anything about this? I've never heard of its
> being investigated like this.
It's not collected anywhere in particular that I know of - but eg a
google for "astatine AtCl" returns 117 mostly-relevant hits, "astatine
CAt4" gives 81, and so on. (My old) CRC covers some simple stuff, but no
useful ref's :(
Much of the basic work was done post-war but long before the internet,
and even before CAS; it may then have been subject to atomic secrecy
requirements: it was never the stuff of much more than an obscure PhD
thesis, usually not even that - and so it's not easy to find. It's out
there, somewhere ~ ~ ~ ~
http://www.triumf.ca/5ISR/40-IS10-HalogenSymposiumWhistler2004a.pdf has
some more modern stuff on At production and use in radiopharmacology.
>
> If At has had this much work done on it, why hasn't radon, which
> is more accessible and at least as theoretically interesting?
There has been a lot more work done on the chemistry of radon than on
astatine - apart from anything else it's easier to work with - but
interesting?
There are a very few known radon compounds, including RnF and RnF2, and
a couple of oxides.
Some might think this interesting, cf the Bartlett kerfuffle with xenon,
but once it had been shown that xenon does form compounds (which was
interesting) it became quite boring imo, just filling in the (m)'s and
(n)'s in XeO(n)F(m), or in this case RnO(m)F(n).
Might be interesting if someone found a compound of Rn with something
other than O or F, but afaik it hasn't happened.
There has also been quite a lot done on radon in re physical processes
in the environment, measuring solubilities, diffusion constants and so
on; and things like appearance, melting and boiling points etc have been
observed/measured (for radon, but not afaict for At).
It probably seems that there has been more work done on At than Rn
(while the opposite is in fact the case) because the chemistry of At is
far more interesting than the chemistry of Rn (in the same way that the
chemistry of I is more interesting the the chemistry of Xe - the results
are more spectacular and varied).
-- Peter Fairbrother
Andrew Usher
> It's not collected anywhere in particular that I know of - but eg a
> google for "astatine AtCl" returns 117 mostly-relevant hits, "astatine
> CAt4" gives 81, and so on. (My old) CRC covers some simple stuff, but no
> useful ref's :(
None of those Google hits lead to any accessible information more than
what's in the Wikipedia article 'Astatine'. You may be right that it
just hasn't been collected, but stuff on radon apparently has been,
and doesn't amount to much.
> > If At has had this much work done on it, why hasn't radon, which
> > is more accessible and at least as theoretically interesting?
>
> There has been a lot more work done on the chemistry of radon than on
> astatine - apart from anything else it's easier to work with - but
> interesting?
>
> There are a very few known radon compounds, including RnF and RnF2, and
> a couple of oxides.
Actually from what I found only RnF2 and RnF+ have been detected. If
there
really are no higher fluorides, that itself is interesting.
True, I couldn't find anything later than 1984, but one would think
the
basic compounds would have been found by then, as they were with
Kr and Xe.
> Some might think this interesting, cf the Bartlett kerfuffle with xenon,
> but once it had been shown that xenon does form compounds (which was
> interesting) it became quite boring imo, just filling in the (m)'s and
> (n)'s in XeO(n)F(m), or in this case RnO(m)F(n).
Actually, known xenon chemistry contains far more compounds than
this. The fact that radon has nothing comparable suggests a paucity
of work, or that something is really funny about radon's chemistry.
> Might be interesting if someone found a compound of Rn with something
> other than O or F, but afaik it hasn't happened.
Rn-Cl bonds really ought to be stable; XeCl+ is even apparently, and
radon
bonds more strongly than Xe.
> There has also been quite a lot done on radon in re physical processes
> in the environment, measuring solubilities, diffusion constants and so
> on; and things like appearance, melting and boiling points etc have been
> observed/measured (for radon, but not afaict for At).
Yes, but almost entirely for the elemental form.
> It probably seems that there has been more work done on At than Rn
> (while the opposite is in fact the case) because the chemistry of At is
> far more interesting than the chemistry of Rn (in the same way that the
> chemistry of I is more interesting the the chemistry of Xe - the results
> are more spectacular and varied).
I'm not sure - we seem to know so little about either. It seems that
the
most important effect theoretically is the effect of the second inert
pair,
which should make At(III) and Rn(IV) more stable, as it does Po(II) -
but
neither of those has been observed!
Andrew Usher
Peter Fairbrother
> Rn-Cl bonds really ought to be stable; XeCl+ is even apparently, and
> radon bonds more strongly than Xe.
?? Any evidence for the last ??
[...]
> It seems that the most important effect theoretically is the effect
> of the second inert pair, which should make At(III) and Rn(IV) more
> stable, as it does Po(II) - but neither of those has been observed!
I believe At(III) has been observed. Can't give a ref offhand though.
However, while the (first) inert pair effect is well-known, it isn't an
accurate description of what really goes on -- that requires
relativistic computations well beyond my ken.
A second inert pair is something else - have a pair of 6p electrons
taken up some s character? Or do you mean the 5s electrons? At these
levels this kind of generalisation doesn't go far however, you need big
computers.
And as far as Rn and At chemistry goes, perhaps you are mistaking
absence of evidence for evidence of absence?
I don't know - but a Prof with a few spare postgrads, the relevant
equipment, and a good At lab technician could easily find new, or at
least obscure, At compounds, probably at a rate of a few per day!
-- Peter Fairbrother
Andrew Usher
> Andrew Usher wrote:
> > Rn-Cl bonds really ought to be stable; XeCl+ is even apparently, and
> > radon bonds more strongly than Xe.
>
> ?? Any evidence for the last ??
>
Well, it should; theoretical treatments say so. So if it does not,
that
would be surprising and interesting, as I said.
> > It seems that the most important effect theoretically is the effect
> > of the second inert pair, which should make At(III) and Rn(IV) more
> > stable, as it does Po(II) - but neither of those has been observed!
>
> I believe At(III) has been observed. Can't give a ref offhand though.
>
> However, while the (first) inert pair effect is well-known, it isn't an
> accurate description of what really goes on -- that requires
> relativistic computations well beyond my ken.
>
> A second inert pair is something else - have a pair of 6p electrons
> taken up some s character?
The 6p1/2 pair, yes, because of spin-orbit splitting. This is expected
to dominate the superheavy p-block elements (113-118) and, as
mentioned, can be observed in Po. Polonium monoxide and
dihalides are all stable.
> And as far as Rn and At chemistry goes, perhaps you are mistaking
> absence of evidence for evidence of absence?
That's what I was trying to ask you about. I don't know how to find
any more journal articles on the subject.
Andrew Usher