sodium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A soft, light, extremely malleable silver-white metallic element that reacts explosively with water, is naturally abundant in combined forms, especially in common salt, and is used in the production of a wide variety of industrially important compounds. Atomic number 11; atomic weight 22.99; melting point 97.8°C; boiling point 892°C; specific gravity 0.971; valence 1. See Table at element.

Century Dictionary and Cyclopedia

1. n. Chemical symbol, Na (natrium); atomic weight, 23. The metallic base of the alkali soda. See soda and metallurgy It was first isolated by Davy, in 1807, by electrolysis, and is at present obtained on a large scale by igniting sodium carbonate with charcoal. Sodium is a silver-white metal with a high luster, but it oxidizes rapidly on exposure to moist air. Heated in the air, it burns rapidly with a bright-yellow fiame, very characteristic of the metal; thrown into cold water, it oxidizes, but does not become hot enough to set the evolved hydrogen on fire, as potassium does; with hot water, ignition of the hydrogen takes place. Its specific gravity at 56° is 0.9735; at the ordinary temperature it has the consistency of wax; at 204° it melts, and forms a liquid resembling mercury in appearance. Next to silver, copper, and gold, it is, of the metals, the best conductor of heat and electricity; next to cæsium, rubidium, and potassium, it is the most electropositive of the metals. It is extensively used in the laboratory as a powerful reducing agent; it is closely analogous to potassium in its chemical relations. Two of its compounds are very widely diffused in nature, and of the highest importance from various points of view; these are common salt and sodium carbonate, or soda.

Wiktionary

1. n. A soft, waxy, silvery reactive metal that is never found unbound in nature, and a chemical element (symbol Na) with an atomic number of 11 and atomic weight of 22.98977.

GNU Webster's 1913

1. n. (Chem.) A common metallic element of the alkali group, in nature always occuring combined, as in common salt, in albite, etc. It is isolated as a soft, waxy, white, unstable metal, so highly reactive that it combines violently with water, and to be preserved must be kept under petroleum or some similar liquid. Sodium is used combined in many salts, in the free state as a reducer, and as a means of obtaining other metals (as magnesium and aluminium) is an important commercial product. Symbol Na (Natrium). Atomic weight 22.990. Specific gravity 0.97.

WordNet 3.0

1. n. a silvery soft waxy metallic element of the alkali metal group; occurs abundantly in natural compounds (especially in salt water); burns with a yellow flame and reacts violently in water; occurs in sea water and in the mineral halite (rock salt)