126 GROUPS I AND IIThe alkali metals have the interesting property of dissolving in
some non-aqueous solvents, notably liquid ammonia, to give clear
coloured solutions which are excellent reducing agents and are
often used as such in organic chemistry. Sodium (for example) forms
an intensely blue solution in liquid ammonia and here the outer (3s)
electron of each sodium atom is believed to become associated with
the solvent ammonia in some way, i.e. the system is Na+(sol vent)
+ e "(solvent).
The solution is energetically unstable (Chapter 3); the sodium
slowly reacts with the ammonia solvent thus:2Na + NH 3 -* 2NaNH 2 + H 2 t
sodium amide (sodamide)(a reaction which can be written 2e~ + 2NH 3 -» 2NH^ + H 2 |).
This reaction is catalysed by such ions as iron(III) and should be
compared to the reaction with water2Na + 2H 2 O -> 2NaOH + H 2 |COMPOUNDS OF GROUP I AND II ELEMENTS
GENERAL
For the most part it is true to say that the chemistry of the alkali
and alkaline earth metal compounds is not that of the metal ion
but rather that of the anion with which the ion is associated. Where
appropriate, therefore, the chemistry of these compounds will be
discussed in other sections, for example nitrates with Group V
compounds, sulphates with Group VI compounds, and only a few
compounds will be discussed here.
THE HYDRIDES
All Group I and II elements, except beryllium, form hydrides by
direct combination with hydrogen. The hydrides of the metals
except those of beryllium and magnesium, are white mainly ionic
solids, all Group I hydrides having the sodium chloride lattice
structure. All the hydrides are stable in dry air but react with water,
the vigour of the reaction increasing with the molecular weight of
the hydride for any particular group.
MH + H 2 O -> MOH -f H 2 T
MH 2 + 2H 2 O -> M(OH) 2 4- H 2 |