Jor
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yellow arsenic?
I read on wiki that just like with phosphorus, there is a yellow allotrope of arsenic, a waxy solid. Can anyone tell me more about this material, is
it very similiar to phosphorus? And how about yellow antinomy? 
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woelen
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Yellow arsenic indeed exists, it has formula As4, but it is much less stable than P4. At room temperature, this compound quickly changes to grey/black
arsenic. It has similar behavior as P4 (which also turns red easily, especially when warm, or in the presence of bright light), but much more
strongly.
I do not know of yellow antimony. Antimony does exist in two allotropes, but the less stable allotrope does not consist of Sb4 molecules.
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not_important
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| Quote: |
1) Yellow antimony. This corresponds to white phosphorus and yellow arsenic: it is transparent and solubile in CS2, and is evidently covalent. It was
prepared by Stock(*) by the action of oxygen on liquid stibine SbH3 at -90 C. It is very unstable. It changes in light at -180, and even in the dark
at -90, into the second form:
2) Black antimony. This is formed from the yellow form, or by the action of oxygen on liquid stibine SbH3 at low temperatures but above -80 C, or by
the rapid cooling of antimony vapour. It is much more chemically active than the ordinary form: it is oxidized by cold air, and is sometimes
pyrophoric. On heating it transforms into the metallic form.
(*) Stock & Guttmann Ber 1904, 37, 885.
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From Sidgwick, The Chemical Elements and Their Compounds
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woelen
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Interesting info from not_important. I did not know of this yellow form of antimony. My old books do not mention it, they only mention the black form
and the metallic form (and some obscure explosive form, which is formed by electrolysing a solution of SbCl3 in conc. HCl and which most likely is
some highly impure form).
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not_important
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Note that the Stock reference is from 1904. I suspect the low stability may have resulting in the yellow form being ignored. Fairly recent
references note that the yellow form is always impure, and suggest it may not be an actual allotrope.
Explosive antimony is a glassy gel of antimony and an antimony trihalide. There is some structure related to the electric current flow used to form
it, so it is not properly amorphous; the explosion is generated by the transformation into the crystalline grey form.
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tapira1
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Yellow As
This is also known as "alpha" arsenic. It is an allotropic variety of arsenic obtained by the rapid condensation of arsenic vapor. Specific Gravity of
3.7 (other sources quote 1.97). It is devoid of metallic properties, but passes into the ordinary "grey" or "metallic" arsenic when exposed to light.
Gray arsenic (spg= 5.73) is the usual stable form, with a melting point of 817°C (28 atm) and sublimation point at 613°C. Gray arsenic is a very
brittle semi-metallic solid. It is steel-gray in color, crystalline, tarnishes readily in air, and is rapidly oxidized to arsenous oxide (As2O3) upon
heating (arsenous oxide exudes the odor of garlic). As you may very well be aware of, arsenic and its compounds are poisonous.
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