On the periodic table, the alkali metals are the elements in group 1.
Group 1 contains lithium, sodium, potassium, rubidium, caesium, and francium. Hydrogen appears at the top of group 1 because it has one electron in its outer shell, but it is not classified as an alkali metal.
The name comes from the alkaline hydroxides formed when these metals react with water. Alkali metals are generally soft, have low melting points compared with many other metals, and react strongly because they readily lose their single valence electron.
Their reactivity usually increases down the group, although experiments with radioactive francium are limited. A common mix-up is group 2, the alkaline earth metals, which have two valence electrons and include magnesium and calcium.