Sodium (symbol Na, atomic number 11, and atomic weight 22,9898) is a chemical a soft metal, reactive and with a low melting point, and a relative density of 0,97 at 20ºC (68ºF). The element’s name comes from the English word soda, which is sometimes used to describe various sodium compounds. From the commercial point of view, sodium is the most important of all the alkaline metals. Sodium reacts quickly with water, and also with snow and ice, to produce sodium hydroxide and hydrogen. When recently cut metallic sodium is exposed to air, it loses its silvery appearance and acquires an opaque grey colour due to the formation of a sodium oxide coating. While sodium can react with ammonia to form sodium amide, it does react with halogens. Sodium and hydrogen react above 200ºC (390ºF) to form sodium hydride.
Sodium also reacts with various metallic halides to generate the metal and sodium chloride. Sodium doesn’t react with paraffinic hydrocarbons, but it forms addition compounds with naphthalene and other aromatic polycyclic compounds and with aryl alkenes. The reaction of sodium with alcohols is similar to the reaction of sodium with water, but slower. There are two general reactions with organic halides. One of them requires the condensation of two organic compounds, which form halogens when those are eliminated. The second type of reaction includes the replacement of halogen by sodium, to obtain a sodium organic compound. 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.
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