Sodium is a soft, silvery-white metal that is the seventh most abundant element and the fifth most abundant metal on Earth. Because it is highly reactive, it is never found in its pure form in nature but only in compounds, including in common table salt (sodium chloride) and many minerals.
Sodium compounds in small quantities are essential for humans and other animals, as well as for some plants, for various functions including regulating blood volume and pressure, conducting nerve impulses, and contracting and relaxing muscles. Sodium chloride accounts for about 0.4 percent of the human body's weight.