The atomic number of sodium is 11. It was discovered in 1807 by the British chemist Sir Humphry Davy . It has a hardness of 0.4. It oxidizes immediately on exposure to air and reacts violently with water , forming sodium hydroxide and hydrogen . The atomic weight of sodium is 22.99.
Sodium is found in nature only in the combined state.
Sodium is prepared commercially by the electrolytic decomposition of fused sodium chloride. Sodium ranks seventh in order of abundance of the elements in the 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.