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Atomic Number: 15
Atomic Symbol: P
Atomic Weight: 30.97376
Electron Configuration: [Ne]3s23p3
History
(Gr. phosphoros, light bearing; ancient name for the planet Venus
when appearing before sunrise) Brand discovered phosphorus in 1669 by preparing
it from urine.
Properties
Phosphorus exists in four or more allotropic forms: white (or
yellow), red, and black (or violet). Ordinary phosphorus is a waxy white solid;
when pure it is colorless and transparent. White phosphorus has two
modifications: alpha and beta with a transition temperature at -3.8°
C.
It is insoluble in water, but soluble in carbon disulfide. It
takes fire spontaneously in air, burning to the pentoxide.
Sources
Never found free in nature, it is widely distributed in combination
with minerals. Phosphate rock, which contains the mineral apatite, an impure
tri-calcium phosphate, is an important source of the element. Large deposits are
found in Russia, in Morocco, and in Florida, Tennessee, Utah, Idaho, and
elsewhere.
Handling
It is very poisonous, 50 mg constituting an approximate fatal dose.
Exposure to white phosphorus should not exceed 0.1 mg/m3 (8-hour
time-weighted average - 40-hour work week). White phosphorus should be kept
under water, as it is dangerously reactive in air, and it should be handled with
forceps, as contact with the skin may cause severe burns.
When exposed to sunlight or when heated in its own vapor to 250°
C, it is converted to the red variety, which does not phosphoresce in air
as does the white variety. This form does not ignite spontaneously and is not as
dangerous as white phosphorus. It should, however, be handled with care as it
does convert to the white form at some temperatures and it emits highly toxic
fumes of the oxides of phosphorus when heated. The red modification is fairly
stable, sublimes with a vapor pressure of 1 atm at 17°
C, and is used in the manufacture of safety matches, pyrotechnics,
pesticides, incendiary shells, smoke bombs, tracer bullets, etc.
Production
White phosphorus may be made by several methods. By one process,
tri-calcium phosphate, the essential ingredient of phosphate rock, is heated in
the presence of carbon and silica in an electric furnace or fuel-fired furnace.
Elementary phosphorus is liberated as vapor and may be collected under
phosphoric acid, an important compound in making super-phosphate fertilizers.
Uses
In recent years, concentrated phosphoric acids, which may contain as
much as 70% to 75% P2O5 content, have become of great
importance to agriculture and farm production. World-wide demand for fertilizers
has caused record phosphate production. Phosphates are used in the production of
special glasses, such as those used for sodium lamps.
Bone-ash, calcium phosphate, is used to create fine chinaware
and to produce mono-calcium phosphate, used in baking powder.
Phosphorus is also important in the production of steels,
phosphor bronze, and many other products. Trisodium phosphate is important as a
cleaning agent, as a water softener, and for preventing boiler scale and
corrosion of pipes and boiler tubes.
Phosphorus is also an essential ingredient of all cell
protoplasm, nervous tissue, and bones.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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