Strontium
Symbol |
Name |
Atomic Number |
Atomic Weight |
Group Number |
Sr |
Strontium |
38 |
87.62 |
2 |
Standard Sate: solid at 298 K
Color: silvery white
Strontium does not occur as the free element. Strontium is softer than calcium and decomposes water more vigorously. Freshly cut strontium has a silvery appearance, but rapidly turns a yellowish colour with the formation of the oxide.
(Na), chemical element of Group Ia of the periodic table (the alkali
metal group).
Properties, occurrence, and uses.
Sodium is a very soft, silvery-white metal. It occurs abundantly in
nature in compounds, especially common salt--sodium chloride
(NaCl)--which forms the mineral halite and comprises about 80
percent of the dissolved constituents of seawater. Sir Humphry Davy
first prepared sodium in its elemental form (1807) by the electrolysis
of fused sodium hydroxide (NaOH). Sodium is the most common
alkali metal and the sixth most abundant element on Earth, comprising
2.8 percent of the Earth's crust; it also occurs in more than trace
amounts in the stars and Sun. Lighter than water, it can be cut with a
knife at room temperature and is brittle at low temperatures. It
conducts heat and electricity easily and exhibits to a marked degree
the photoelectric effect (emission of electrons when exposed to light).
Sodium reacts vigorously with water to give hydrogen (which may
ignite from the heat of the reaction) and sodium hydroxide. The
metal is extremely active chemically, easily unites with oxygen of the
air, and usually must be kept immersed in an inert atmosphere such as
nitrogen or in inert liquids such as kerosene or naphtha. Because
sodium is so reactive, it never occurs in the free state in nature. It is
commercially produced by electrolyzing sodium chloride.
Inexpensive and available in tank-car quantities, sodium is widely
used in the manufacture of chemicals and pharmaceuticals, in
metallurgy, as a heat exchanger in atomic reactors and certain types
of engines, and in sodium vapour lamps.
Natural sodium is the stable isotope of mass 23. Of the six
radioactive, artificial isotopes, sodium-22 (2.6-year half-life) is used
as a radioactive tracer for natural sodium, sodium-24 (15-hour
half-life) is limited in use by its short life, and the rest have half-lives
of a minute or less. The yellow colour of the sodium vapour lamp
and the sodium flame (the basis of an analytical test for sodium) is
identified with two prominent lines in the yellow portion of the light
spectrum.
Principal compounds.
Sodium is highly reactive, forming a wide variety of compounds with
nearly all inorganic and organic anions. It has a valence of +1, and its
single valence electron is lost with great ease, yielding the colourless
sodium ion (Na+).
Sodium hydroxide (NaOH) is a corrosive, white crystalline solid that
readily absorbs moisture until it liquefies. Commonly called caustic
soda, or lye, sodium hydroxide is the most widely used industrial
alkali. It is highly corrosive to animal and vegetable tissue. The
alkaline solutions it forms when dissolved in water neutralize acids in
various commercial processes: in petroleum refining, it removes
sulfuric and organic acids; in soapmaking, it reacts with fatty acids. In
the making of cellophane, paper, viscose rayon, and other products, its
alkaline solutions enter into the treatment of cellulose and into the
manufacture of many chemicals.
The most important and familiar sodium compound is sodium
chloride, or common salt, NaCl. Most other sodium compounds are
prepared either directly or indirectly from sodium chloride, which
occurs in seawater, in natural brines, and as rock salt. Other major
commercial applications of sodium chloride include its use in the
manufacture of chlorine and sodium hydroxide by electrolytic
decomposition and in the production of sodium carbonate (Na2CO3)
by the Solvay process. The electrolysis of sodium chloride produces
sodium hypochlorite, NaOCl, a compound of sodium, oxygen, and
chlorine used in large quantities in household chlorine bleach. Sodium
hypochlorite is also utilized as an industrial bleach for paper pulp and
textiles, for chlorination of water, and in certain medicinal
preparations as an antiseptic and a fungicide. It is an unstable
compound known only in aqueous solution.
Sodium nitrate, or soda nitre, NaNO3, is commonly called Chile
saltpetre after its mineral deposits in northern Chile, the principal
source. Sodium nitrate is used as a nitrogenous fertilizer and as a
component of dynamite.
Sodium sulfate, Na2SO4, is a white crystalline solid or powder
employed in the manufacture of kraft paper, paperboard, glass, and
detergents and as a raw material for the production of various
chemicals. It is obtained either from deposits of the sodium sulfate
minerals mirabilite and thenardite or synthetically by the treatment of
sodium chloride with sulfuric acid. The crystallized product is a
hydrate, Na2SO410H2O, commonly known as Glauber's salt. Sodium
thiosulfate (sodium hyposulfite), Na2S2O3, is used by photographers
to fix developed negatives and prints; it acts by dissolving the
unchanged silver salts.
Other familiar sodium compounds are the carbonates, which contain
the carbonate ion (CO32-). Sodium bicarbonate, also called sodium
hydrogen carbonate, or bicarbonate of soda, NaHCO3, is a source of
carbon dioxide and so is used as an ingredient in baking powders, in
effervescent salts and beverages, and as the main constituent of
dry-chemical fire extinguishers. Its slight alkalinity makes it useful in
treating gastric or urinary hyperacidity and acidosis. It is also
employed in certain industrial processes, as in tanning and the
preparation of wool. Sodium carbonate, or soda ash, Na2CO3, is
widely distributed in nature, occurring as constituents of mineral
waters and as the solid minerals natron, trona, and thermonatrite.
Large quantities of this alkaline salt are used in making glass,
detergents, and cleansers. Sodium carbonate is treated with carbon
dioxide to produce sodium bicarbonate. The monohydrate form of
sodium carbonate, Na2CO3H2O, is employed extensively in
photography as a constituent in developers. Washing soda (sal soda)
consists of sodium carbonate decahydrate, Na2CO310H2O; it serves
as a bleach for cotton and linen and as a household cleansing agent.
atomic number 11 atomic weight 22.9898 melting point 97.81 C (208
F) boiling point 882.9 C (1,621 F) specific gravity 0.971 (20 C)
valence 1 electronic config. 2-8-1 or 1s22s22p63s1
"sodium" Encyclop�dia Britannica Online.
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