Sodium. Pieces of the reactive metallic element sodium (Na) stored under oil in a jar. This soft alkali metal reacts rapidly with the water and oxygen in the air. The protective oil layer prevents this from happening. Sodium is not found in its elemental form in nature, due to it being highly reactive, and is mainly found in the salt (sodium chloride) of salt deposits and sea water. Sodium is obtained by the electrolysis of sodium chloride. Numerous sodium compounds are manufactured by the chemical industry and have wide-ranging uses.