Sodium

Sodium is a soft metal that can be cut easily with a table knife. Its density is so low that it will float when placed into water. At the same time, the metal is so active that it reacts violently with the water, producing sodium hydroxide and hydrogen gas as products. Sufficient heat is produced in the reaction to cause the metal to heat and to ignite the hydrogen produced in the reaction.

Freshly cut sodium metal has a bright, shiny surface that quickly becomes a dull gray as it reacts with oxygen in the air around it. Over time, the metal becomes covered with a white crust of sodium oxide that prevents further reaction of the metal and oxygen.

Sodium forms a very large number of compounds in nature, and an even larger number have been prepared synthetically. These compounds include binary compounds of sodium with metals, non-metals, and metalloids, as well as ternary, and more complex compounds. Included among these are such well-known substances as sodium chloride (table salt), sodium bicarbonate (baking soda), sodium borate (borax), sodium carbonate (soda ash), monosodium glutamate (MSG), sodium hydroxide (caustic soda or lye), sodium nitrate (Chilean saltpeter), sodium silicate (water glass), and sodium tartrate (sal tartar).