Alloys of alkali metals exist that melt as low as −78 °C (−109 °F).The alkali metals react readily with atmospheric oxygen and water vapour.Gustav Kirchhoff were investigating the mineral waters in the Palatinate in 1860, they obtained a filtrate that was characterized by two lines in the blue region of its spectrum (the light emitted when the sample was inserted into a , used to designate the blue of the sky.
As with other metals, such a partially filled valence band is a conduction band and is responsible for the valence properties typical of metals.
As a result, the alkali metals tend to form singly charged positive ions (cations) when they react with nonmetals.
The compounds that result have high melting points and are hard crystals that are held together by ionic bonds (resulting from mutually attractive forces that exist between positive and negative electrical charges).
A very dilute gas of atomic sodium (about 1,000 atoms per cubic cm [about 16,000 atoms per cubic inch]) is produced in Earth’s mesosphere (altitude about 90 km [60 miles]) by ablation of meteors.
Subsequent reaction of sodium with ozone and atomic oxygen produces excited sodium atoms that emit the light we see as the “tail” of a meteor as well as the more diffuse atmospheric nightglow.