Physical properties of group 1 metals

General properties

The alkali metals illustrate, more clearly than any other group of elements, the influence of increase in atomic and ionic size on physical and chemical properties. Thus, the group 1 metals are often chosen to illustrate general principles. Some physical properties of the group 1 metals are given in Table 1.1.

• With increasing atomic number, the atoms become larger and the strength of metallic bonding  decreases.
• The effect of increasing size evidently outweighs that of increasing nuclear charge, since the ionization energies decrease from Li to Cs. The values of IE₂ for all the alkali metals are so high that the formation of M₂ ions under chemically reasonable conditions is not viable.
• Values of Eo _M+‏/M are related to energy changes accompanying the processes:

and down group 1, differences in these energy changes almost cancel out, resulting in similar E^o_M+/M values. The lower reactivity of Li towards H₂O is kinetic rather than thermodynamic in origin; Li is a harder and higher melting metal, is less rapidly dispersed, and reacts more slowly than its heavier congeners. In general, the chemistry of the group 1 metals is dominated by compounds containing M‏ ions.

    Considerations of lattice energies calculated using an electrostatic model provide a satisfactory understanding for the fact that ionic compounds are central to the chemistry of Na, K, Rb and Cs. That Li shows a so-called ‘anomalous’ behaviour and exhibits a diagonal relationship to Mg can be explained in terms of similar energetic considerations.