alkali metals, metals found in Group 1 of the periodic table. Compared to other metals they are soft and have low melting points and densities. Alkali metals are powerful reducing agents and form univalent compounds. All react violently with water, releasing hydrogen and forming hydroxides. They tarnish rapidly even in dry air. They are never found uncombined in nature. In order of increasing atomic number the alkali metals are lithium, sodium, potassium, rubidium, cesium, and francium.