    sodium . is a chemical element with symbol&nbsp;na (from ) and atomic number&nbsp;11. it is a soft, silver-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23na. the free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by humphry davy in 1807 by the electrolysis of sodium hydroxide. sodium is the sixth most abundant element in the earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt (nacl). many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that sodium and chlorine (cl) are the most common dissolved elements by weight in the earth's bodies of oceanic water. many sodium compounds are useful, such as sodium hydroxide (lye) for soap-making, and sodium chloride for use as a de-icing agent and a nutrient (edible salt). sodium is an essential element for all animals and some plants. in animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. the consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral. ==characteristics== ===physical=== sodium at standard temperature and pressure is a soft silvery metal, that oxidizes to grayish white unless immersed in oil or inert gas. sodium can be readily cut with a knife, and is a good conductor of electricity. these properties change dramatically at elevated pressures: at 1.5 mbar, the color changes from silvery metallic to black; at 1.9 mbar the material becomes transparent, with a red color; and at 3 mbar sodium is a clear and transparent solid. all of these high-pressure allotropes are insulators and electrides. when sodium or its compounds are introduced into a flame, they turn it yellow,{{cite book|last=schumann|first=walter|title=minerals of the world|date=5 august 2008|publisher=sterling|isbn=9
Alkali_metals Biology_and_pharmacology_of_chemical_elements Chemical_elements Desiccants Dietary_minerals Nuclear_reactor_coolants Reducing_agents Sodium Sodium_compounds Sodium_minerals