Sodium

Sodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals. It has only one stable isotope, 23Na.

Elemental sodium was first isolated by Sir Humphry Davy in 1807 by passing an electric current through molten sodium hydroxide. Elemental sodium does not occur naturally, because it quickly oxidizes in air and is violently reactive with water, so it must be stored in an inert medium, such as a liquid hydrocarbon. The free metal is used for some chemical synthesis, analysis, and heat transfer applications. Sodium ion is soluble in water in nearly all of its compounds. Sodium ion is also a component of many minerals. Sodium is an essential element for all animal life and for some plant species. In animals, sodium ions are used in opposition to potassium ions, to allow the organism to build up an electrostatic charge on cell membranes, and thus allow transmission of nerve impulses when the charge is allowed to dissipate by a moving wave of voltage change. Sodium is thus classified as a “dietary inorganic macro-mineral” for animals.

Characteristics

At room temperature, sodium metal is soft enough that it can be cut with a knife. In air, the bright silvery luster of freshly exposed sodium will rapidly tarnish. The density of alkali metals generally increases with increasing atomic number, but sodium is denser than potassium. Sodium is a fairly good conductor of heat. Compared with other alkali metals, sodium is generally less reactive than potassium and more reactive than lithium, in accordance with "periodic law": for example, their reaction in chlorine gas, etc. Sodium reacts exothermically with water: small pea-sized pieces will bounce across the surface of the water until they are consumed by it, whereas large pieces will explode. While sodium reacts with water at room temperature, the sodium piece melts with the heat of the reaction to form a sphere, if the reacting sodium piece is large enough. The reaction with water produces very caustic sodium hydroxide and highly flammable hydrogen gas. These are extreme hazards. When burned in air, sodium forms sodium peroxide Na2O2, or with limited oxygen, the oxide Na2O (unlike lithium, the nitride is not formed). If burned in oxygen under pressure, sodium superoxide NaO2 will be produced.

Value

The base value of each unit of ranges between 1 and 10Ð per unit, with up to 3 units being found at any one time.

Presence on Mars: Common