Groups I and II
(Lithium, sodium, potassium, rubidium, caesium;
beryllium, magnesium, calcium, strontium,
barium)THE ELEMENTS
GENERAL CHARACTERISTICS
These elements form two groups, often called the alkali (Group I)
and alkaline earth (Group II) metals. Some of the physical properties
usually associated with metals—hardness, high m.p. and b.p.—are
noticeably lacking in these metals, but they all have a metallic
appearance and are good electrical conductors. Table 6.1 gives some
of the physical properties.
From Table 6.7, it is easy to see that Group II metals are more
dense, are harder and have higher m.p. and b.p. than the corres-
ponding Group I metals.
In Chapter 2, a discussion of the theory of metallic bonding
indicated that the strength of such bonding generally depends on
the ratio (number of electrons available for bonding)/(atomic size).
The greater this ratio is, the stronger are the bonds between the
metal atoms. In the pre-transition metals, this ratio is small and at a
minimum in Group I with only one bonding electron. Metallic
bond strength is greater in Group II but there are still only two
bonding electrons available, hence the metals are still relatively soft
and have low melting and boiling points. Hardness, m.p. and b.p.
all decrease steadily down Group I, the metallic bond strength
decreasing with increasing atomic radius. These changes are not so
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