Modern inorganic chemistry

GROUPV 213

The phosphine produced is impure and contains small quantities

of diphosphane, P 2 H 4 (p. 227).

Arsenic, unlike phosphorus, is only slightly attacked by boiling

sodium hydroxide; more rapid attack takes place with the fused

alkali; an arsenate(III) is obtained in both cases,

As 4 4- 12OKT -

cf. aluminium (p. 144). Arsine is not formed in this reaction.

Antimony and bismuth do not react with sodium hydroxide.

4. Reaction with halogens

Nitrogen does form a number of binary compounds with the halo-

gens but none of these can be prepared by the direct combination

of the elements and they are dealt with below (p. 249). The other

Group V elements all form halides by direct combination.

PHOSPHORUS

White and red phosphorus combine directly with chlorine, bromine

and iodine, the red allotrope reacting in each case at a slightly

higher temperature. The reactions are very vigorous and white

phosphorus is spontaneously inflammable in chlorine at room

temperature. Both chlorine and bromine first form a trihalide:

P 4 4- 6X 2 -> 4PX 3 (X = Cl or Br)

but this is converted to a pentahalide by excess of the halogen. No

pentaiodide is known (p. 316).

ARSENIC, ANTIMONY AND BISMUTH

A complete set of trihalides for arsenic, antimony and bismuth can
be prepared by the direct combination of the elements although
other methods of preparation can sometimes be used. The vigour of
the direct combination reaction for a given metal decreases from
fluorine to iodine (except in the case of bismuth which does not
react readily with fluorine) and for a given halogen, from arsenic to
bismuth.
In addition to the trihalides, arsenic and antimony form penta-
fluorides and antimony a pentachloride; it is rather odd that
arsenic pentachloride has not yet been prepared.