alkali metals

The elements of group 1 (formerly called group Ia in North America and group Ib in Europe), include the metals lithium, sodium, potassium, rubidium, cesium and francium. Because these elements react violently with water to form strong bases, or alkalis, they are collectively known as the alkali metals, characterized by low density, low melting points and high ductility. Never found in nature as free elements, the alkali metals occur in compounds like chlorides or silicates. The monovalent alkali metals form stable salts by donating an electron to a halogen atom. The higher the atomic number, the more reactive is the alkali metal.