Overview

Sodium is a chemical element commonly represented by the symbol Na and identified by atomic number 11. It has a standard atomic mass near 22.9898 atomic mass units. As a pure metal it is soft and silvery, with a relatively low melting point compared with most metals. In nature sodium is most often encountered as ions in minerals and dissolved salts rather than as the free metal; the largest natural reservoir is sea water, where sodium salts contribute to salinity. For a concise technical overview see the general element summary.

Physical and chemical characteristics

Sodium belongs to the alkali metal group, a set of elements characterized by a single valence electron and vigorous chemical reactivity. Metallic sodium oxidizes in air and reacts exothermically with water to produce sodium hydroxide and hydrogen gas; under some conditions the reaction can ignite the hydrogen. Because of this reactivity, metallic sodium is handled under hydrocarbon oil or in inert atmospheres. It is a good electrical conductor and forms a variety of alloys and intermetallic compounds, including low-melting liquid alloys used in heat-transfer applications.

Common compounds and applications

Many familiar uses of sodium arise from its compounds rather than the metal itself. Important examples include:

  • Sodium chloride (NaCl) — common table salt, a major natural source of sodium used in food, de-icing and industrial processes.
  • Sodium hydroxide (NaOH) — a strong caustic alkali used in chemical manufacture, papermaking and cleaning agents.
  • Sodium carbonate and bicarbonate — used in glassmaking, water treatment, baking and as buffering agents.
  • Specialty uses — sodium vapor lamps for street lighting, reducing agents in organic and inorganic synthesis, and some reactor and heat-transfer roles in industry.

Occurrence, isotopes and atomic data

Sodium is one of the most abundant elements in the Earth’s crust and in ocean water. Natural sodium is overwhelmingly the stable isotope 23Na; other isotopes are radioactive and present only in trace amounts or produced artificially for research and tracer studies. Reference data on isotopic composition and atomic mass are compiled in standard tables and databases (atomic mass data).

History and production

The element was first isolated in the early 19th century by electrolysis of molten alkali compounds. Historically, Michael Faraday and Humphry Davy pioneered electrolytic methods for producing elemental sodium and other alkali metals. Industrially, sodium metal has been produced by the electrolysis of molten sodium chloride or by other high-temperature reduction methods; large-scale production today focuses mainly on sodium compounds rather than the free metal.

Biological role and safety

Sodium ions are essential electrolytes in animals and humans. They contribute to fluid balance, influence blood pressure, and play a central role in nerve impulse transmission and muscle contraction via membrane transport systems such as the sodium–potassium pump. From a handling perspective, metallic sodium is hazardous: it reacts violently with water and moist air and can cause fires or chemical burns. Proper precautions include storage under oil or inert gas, use of protective equipment, and avoidance of contact with water. Detailed safety and regulatory guidance is available from chemical safety resources and material safety data sheets (element summary, atomic mass tables).