II.

Properties and Occurrence

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.