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Sodium, with chemical symbol Na and atomic number 11, is a soft, silvery‑white alkali metal. It is highly reactive and oxidizes rapidly in air, so pure sodium is stored under oil or in an inert atmosphere. In nature it does not occur freely; it is the sixth most abundant element in the Earth's crust, mainly found in compounds such as halite (rock salt) and other sodium salts.

Natural sodium has one stable isotope, sodium‑23. The element was first isolated by Humphry Davy in 1807 through the electrolysis of molten sodium hydroxide. The name sodium derives from the Latin natrium, from which the chemical symbol Na is also taken.

Sodium occurs primarily as the chloride ion in seawater and in many minerals. Industrial production of sodium metal is dominated by electrolysis of molten sodium chloride in a Downs cell, which yields sodium metal and chlorine gas. The most widely used sodium compound is sodium chloride (table salt), essential for seasoning and food preservation. Other important sodium compounds include sodium hydroxide (caustic soda) and sodium bicarbonate (baking soda).

Biologically, sodium ions (Na+) are essential electrolytes in animals and humans. They regulate fluid balance, transmit nerve impulses, and enable muscle contraction. Health guidelines typically limit sodium intake to about 2,300 milligrams per day for adults, with lower targets for some populations. Excessive sodium intake is associated with elevated blood pressure and cardiovascular risk; dietary reductions may benefit certain individuals.

Safety and handling: Sodium reacts violently with water, producing sodium hydroxide and hydrogen gas. It must be stored away from moisture and handled with appropriate precautions to prevent contact with air and water.