Modern inorganic chemistry

228 GROUPV

2. OXIDES

The principal oxides formed by Group V elements and their formal

oxidation states are given below:

Element

Oxidation state

-hi

+ 3

+ 4

+ 5

N P

N 2 O

NO

N 2 O 3 P 4 O 6

NO 2 , N 2 O 4

N 2 O 5 P 4 O 10

As

As 4 O 6

As 2 O 5

Sb Bi

Sb 4 O 6 Bi 2 O 3

Sb 2 O 5

Nitrogen is unusual in forming so many oxides. The acidity of the

Group V oxides falls from phosphorus, whose oxides are acidic,

through arsenic and antimony whose oxides are amphoteric, to the

basic oxide oFbismuth. This change is in accordance with the change

from the non-metallic element, phosphorus, to the essentially

metallic element, bismuth. The -f 5 oxides are found, in each case,

to be more acidic than the corresponding + 3 oxides.

Oxides of nitrogen

DIN1TROGEN OXIDE (NITROUS OXIDE). N 2 O

This can be prepared by the controlled reduction of a nitrite
(nitrate(III)) or nitrate. Cautious heating of ammonium nitrate gives
dinitrogen oxide by an Internal' oxidation-reduction process:

NH 4 NO 3 ^N 2 Ot 4- 2H 2 O

Too rapid heating produces explosive decomposition. The reaction
between hydroxyammonium chloride, NH 3 OH+ ,C1~, and sodium
nitrite gives pure dinitrogen oxide:

NH 3 OH+ + NO 2 ~ -* N 2 Ot + 2H 2 O

Dinitrogen oxide is a colourless gas; the molecule has the geometric
structure N—N—O, and is a resonance hybrid of the two forms

N=N=O N==N—O

i.e. .''N * N : O: ] and [i.e. :N ; N £ 6: