Modern inorganic chemistry

GROUPV 207

Bi(OH) 3 is insoluble in alkali but readily soluble in acids to form

salts.

The outer quantum level of the Group V elements contains five

electrons, but there is no tendency for the elements at the top of the

group to lose these and form positive ions. Nitrogen and phosphorus

are, in fact, typical non-metals, having acidic oxides which react with

alkalis to give saks. Nitrogen, the head element, shows many

notable differences from the other Group V elements, the distinction

arising from the inability of nitrogen to expand the number of

electrons in its outer quantum level beyond eight. (The other

Group V elements are able to use d orbitals in their outer quantum

level for further expansion.) The nitrogen atom can (a) share three

electrons to give a covalency of three, leaving a lone pair of electrons

on the nitrogen atom, (b) share three electrons and donate the

unshared pair to an acceptor atom or molecule, as in NH^,

//°

H 3 N-»A1C1 3 and nitric acid H—O—N when nitrogen achieves

XO

its maximum covalency of four, (c) acquire three electrons when
combining with very electropositive elements to form the nitride
ion, N^3 ~.
The other Group V elements can behave in a similar manner but
their atoms have an increasing reluctance to accept electrons, and
to donate the lone pair. These atoms can, however, increase their
covalency to five, for example in the vapour of phosphorus penta-
chloride, or even to six, for example in the ions [PF 6 ]~, [PC1 6 ]~.
Hence phosphorus, arsenic, antimony and bismuth are able to form
both trivalent and pentavalent compounds but as we go from
phosphorus to bismuth it becomes increasingly more difficult to
achieve a pentavalent state—thus phosphorus(V) oxide, P 4 O 10 , is
readily obtained by burning phosphorus in excess air, but the
corresponding oxides of antimony and bismuth require the action
of strong oxidising agents for their preparation and bismuth(V)
oxide is particularly unstable.

THE ELEMENTS: THEIR OCCURRENCE AND

EXTRACTION

NITROGEN

Nitrogen is an essential constituent of all living matter, being one

of the elements present in proteins. Proteins are synthesised by