From the English word, soda; Medieval Latin, sodanum: a headache remedy. Long recognized in compounds, sodium was first isolated by Davy in 1807 by electrolysis of caustic soda.
Sodium is present in fair abundance in the sun and stars. The D lines of sodium are among the most prominent in the solar spectrum. Sodium is the fourth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals.
It is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride. This method is much cheaper than that of electrolyzing sodium hydroxide, as was used several years ago.
The most common compound is sodium chloride (table salt), but it occurs in many other minerals, such as soda niter, cryolite, amphibole, zeolite, etc.
Sodium compounds are important to the paper, glass, soap, textile, petroleum, chemical, and metal industries. Soap is generally a sodium salt of certain fatty acids. The importance of common salt to animal nutrition has been recognized since prehistoric times.
Among the many compounds that are of the greatest industrial importance are common salt (NaCl), soda ash (Na2CO3), baking soda (NaHCO3), caustic soda (NaOH), Chile saltpeter (NaNO3), di- and tri-sodium phosphates, sodium thiosulfate (hypo, Na2S2O3 • 5H2O), and borax (Na2B4O7 • 10H2O).
Metallic sodium is vital in the manufacture of esters and in the preparation of organic compounds. The metal may be used to improve the structure of certain alloys, descale metal, and purify molten metals.
An alloy of sodium with potassium, NaK, is an important heat transfer agent.
Thirteen isotopes of sodium are recognized.