Modern inorganic chemistry

GROUPS I AND II 125

REACTIONS OF THE METALS

In general, the metals of Groups I and II can combine, more or less
readily, with many less electropositive elements. The reactivity
towards most reagents, for example dry oxygen and dry bromine,
increases as the size of the atom increases and the ionisation energy
falls. However, when reacting with very small non-metallic elements,
for example carbon and nitrogen, the reverse is true, since the very
small cation and the very small anion produced in the reaction form
a very strong crystal lattice. The lattice energy evolved is sufficiently
great to more than compensate for the large ionisation energy of
the small atom. Hence, although all Group II elements form
nitrides, only lithium amongst the alkali metals is able to do so.
Most of the metals react with water and, therefore, with any
aqueous solution giving effectively M+ (Group I) and M2+ (Group
II) ions.

Group 1: 2M + 2H 2 O -> 2M + (aq) + 2OH" + H 2 |

Group II: M + 2H 2 O -» M^2 + (aq) 4- 2OH~ 4- H 2 T

The reactions with water are summarised in Table 6.3. Since the
metals are powerful reducing agents (p. 98) they cannot be pre-
pared in aqueous solution; electrolysis of the fused anhydrous
halides is usually employed using a graphite anode.

Table 6.3

Element

Reaction
conditions

Basic
properties
of products

Element

Li Na K Rb Cs

All react with cold water to produce MOH.

Vigour of reaction increasing

All basic, base strengthincreasing

Be Mg Ca Sr Ba

Reaction
conditions

Basic
properties
of product

Does not Very slowly

react with with water,

water readily with

steam

React with cold water.

vigour of reaction increasing.

Be(OH) 2 MgO

amphoteric insoluble slightly_

soluble"

M(OH) (^2) • soluble
Base strength increasing