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atomic number of sodium, atomic weight of sodium, soft metallic element, Na2O2, Chile saltpeter

Sodium, symbol Na, highly reactive, silvery-white, extremely soft metallic element. In group 1 (or Ia) of the periodic table, sodium is one of the alkali metals. The atomic number of sodium is 11. It was discovered in 1807 by the British chemist Sir Humphry Davy. The element’s name comes from the English word soda, which is sometimes used to describe various sodium compounds.

Properties and Occurence

Elemental sodium is metal that is soft enough to be cut with a knife. It has a hardness of 0.4. It oxidizes immediately on exposure to air and reacts violently with water, forming sodium hydroxide and hydrogen. Sodium melts at about 98°C (208°F), boils at about 883°C (about 1621°F), and has a specific gravity of 0.97. The atomic weight of sodium is 22.99.

Sodium is found in nature only in the combined state. It occurs in the ocean and in salt lakes as sodium chloride, NaCl, and less often as sodium carbonate, Na2CO3, and sodium sulfate, Na2SO4. Sodium is prepared commercially by the electrolytic decomposition of fused sodium chloride. Sodium ranks seventh in order of abundance of the elements in Earth's crust. It is a necessary constituent of plant and animal tissue.


The element is used in the manufacture of tetraethyl lead and as a cooling agent in nuclear reactors. The most important compound of sodium is sodium chloride, known commonly as salt. Other important compounds include sodium carbonate, known as washing soda, and sodium bicarbonate, known as baking soda. Sodium hydroxide, known commercially as soda lye or caustic soda, is used in the manufacture of soap, rayon, and paper, in oil refining, and in the textile and rubber industries. Sodium tetraborate is known commonly as borax. Sodium fluoride, NaF, is used as an antiseptic, as a poison for mice and roaches, and in ceramics. Sodium nitrate, known as Chile saltpeter, is used as a fertilizer. Sodium peroxide, Na2O2, is an important bleaching and oxidizing agent. Sodium thiosulfate, Na2S2O3 · 5H2O, known as hypo, is used in photography as a fixing agent.

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