We note first that the elements are all electropositive, having
relatively low ionisation energies, and are, in consequence, very
reactive. The enthalpy change required for the process M(metal) -»
M + (g) for Group I, or M(metal) -> M2+(g) for Group II is at a
maximum at the top of each group, and it is, therefore, not surprising
to find that lithium, beryllium and, to some extent, magnesium do
form some covalent compounds. Most solid compounds of Group 1
and II elements, however, have ionic structures and the properties
associated with such structures—high m.p. and b.p., solubility in
water rather than in organic solvents and electrical conductance
when molten.