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~The family.~ The metals listed in the above table constitute the even
family in Group I in the periodic arrangement of the elements, and
therefore form a natural family. The name alkali metals is commonly
applied to the family for the reason that the hydroxides of the most
familiar members of the family, namely sodium and potassium, have long
been called alkalis.

1. _Occurrence._ While none of these metals occur free in nature, their
compounds are very widely distributed, being especially abundant in sea
and mineral waters, in salt beds, and in many rocks. Only sodium and
potassium occur in abundance, the others being rarely found in any
considerable quantity.

2. _Preparation._ The metals are most conveniently prepared by the
electrolysis of their fused hydroxides or chlorides, though it is
possible to prepare them by reducing their oxides or carbonates with
carbon.

3. _Properties._ They are soft, light metals, having low melting points
and small densities, as is indicated in the table. Their melting points
vary inversely with their atomic weights, while their densities (sodium
excepted) vary directly with these. The pure metals have a silvery
luster but tarnish at once when exposed to the air, owing to the
formation of a film of oxide upon the surface of the metal. They are
therefore preserved in some liquid, such as coal oil, which contains no
oxygen. Because of their strong affinity for oxygen they decompose water
with great ease, forming hydroxides and liberating hydrogen in
accordance with the equation

M + H_{2}O = MOH + H,

where M stands for any one of these metals. These hydroxides are white
solids; they are readily soluble in water and possess very strong basic
properties. These bases are nearly equal in strength, that is, they all
dissociate in water to about the same extent.

4. _Compounds._ The alkali metals almost always act as univalent
elements in the formation of compounds, the composition of which can be
represented by such formulas as MH, MCl, MNO_{3}, M_{2}SO_{4},
M_{3}PO_{4}. These compounds, when dissolved in water, dissociate in
such a way as to form simple, univalent metallic ions which are
colorless. With the exception of lithium these metals form very few
insoluble compounds, so that it is not often that precipitates
containing them are obtained. Only sodium and potassium will be studied
in detail, since the othe