Phosphorus, Elemental

CAS RN: 7723-14-0

Other Properties

Vapor pressure: 0.181 mm Hg at melting point (44.1 deg C)
White: Heat capacity = 0.769 J/g-K
Red: Triple point = 590 deg C; sublimation point = 431 deg C
Black: Melting point = 610 deg C
Heat of fusion = 2.5X10+6 J/kg-mol
Density = 1.74 g/cu cm at 50 deg C (liquid)
Phosphorus vapor exists as P4 molecules until dissociation to P2 begins at 800 deg C. Essentially all the vapor is P2 at 1500 deg C, but further dissociation to monatomic P is less that 0.1% at that temperature.
Volatile; sublimes in vacuo at ordinary temp when exposed to light. When exposed to air in the dark, emits a greenish light and gives off white fumes. Ignites at about 30 deg in moist air; the ignition temp is higher when the air is dry. Darkens on exposure to light.
Combines directly with the halogens to form tri- or pentahalides; combines with sulfur to form sulfides. Reacts with several metals to form phosphides. Yields orthophosphoric acid when treated with nitric acid. Reacts with alkali hydroxides with formation of phosphine and sodium hypophosphite.
Black: Orthorhombic crystalline forms: stable in air; resembles graphite in texture; density 2.691. Does not catch fire spontaneously. Amorphous form prepared at lower pressures. At higher pressure the orthorhombic form undergoes reversible transition to a rhombohedral structure, density 3.56, and a cubic structure, density 3.83.
Red: The properties of red phosphorus are intermediate between those of the white and black forms. Density 2.34. Insoluble in organic solvents. Soluble in phosphorus tribromide. Less active than the white form; reacts only at high temperature. Yields the white modification when distilled at 290 deg C. Catches fire when heated in air to about 260 deg C and burns with formation of the pentoxide. Burns when heated in an atmosphere of chlorine.
Atomic number 15; valences 3, 5. One naturally occurring isotope: 31P; artificial, radioactive isotopes: 28-30; 32-34. Does not occur free in nature.
White phosphorus burns rapidly in air to form phosphoric oxide.
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