Phosphorus

Phosphorus, ₁₅P
	waxy white (yellow cut), red (granules centre left, chunk centre right), and violet phosphorus
General properties
Pronunciation	/ˈfɒsfərəs/ (FOS-fər-əs)
Appearance	Colourless, waxy white, yellow, scarlet, red, violet, black
Standard atomic weight (Ar, standard)	30.973761998(5)
Abundance
in the Earth's crust	5.2 (taking silicon as 100)
Phosphorus in the periodic table
	silicon ← phosphorus → sulfur
Atomic number (Z)	15
Group	group 15 (pnictogens)
Period	period 3
Element category	polyatomic nonmetal
Block	p-block
Electron configuration	[Ne] 3s2 3p3
Electrons per shell	2, 8, 5
Physical properties
Phase at STP	solid
Density (near r.t.)	white: 1.823 g·cm−3; red: ≈ 2.2–2.34 g·cm−3; violet: 2.36 g·cm−3; black: 2.69 g/cm3
Heat of fusion	white: 0.66 kJ/mol
Heat of vaporisation	white: 51.9 kJ/mol
Molar heat capacity	white: 23.824 J/(mol·K)
Atomic properties
Oxidation states	5, 4, 3, 2, 1, −1, −2, −3 (a mildly acidic oxide)
Electronegativity	Pauling scale: 2.19
Ionisation energies	1st: 1011.8 kJ/mol; 2nd: 1907 kJ/mol; 3rd: 2914.1 kJ/mol; (more);
Covalent radius	107±3 pm
Van der Waals radius	180 pm
	Spectral lines
	Spectral lines
Miscellanea
Crystal structure	body-centred cubic (bcc)
Thermal conductivity	white: 0.236 W/(m·K); black: 12.1 W/(m·K)
Magnetic ordering	white, red, violet, black: diamagnetic
Magnetic susceptibility	−20.8·10−6 cm3/mol (293 K)
Bulk modulus	white: 5 GPa; red: 11 GPa
CAS Number	7723-14-0 (red); 12185-10-3 (white)
History
Discovery	Hennig Brand (1669)
Recognised as an element by	Antoine Lavoisier (1777)
Main isotopes of phosphorus
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Phosphorus is a chemical element with symbol P and atomic number 15. As an element, phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Earth. With a concentration of 0.099%, phosphorus is the most abundant pnictogen in the Earth's crust. Other than a few exceptions, minerals containing phosphorus are in the maximally oxidized state as inorganic phosphate rocks.

The first form of elemental phosphorus that was produced (white phosphorus, in 1669) emits a faint glow when exposed to oxygen – hence the name, taken from Greek mythology, Φωσφόρος meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star", the planet Venus (or Mercury). The term "phosphorescence", meaning glow after illumination, originally derives from this property of phosphorus, although this word has since been used for a different physical process that produces a glow. The glow of phosphorus itself originates from oxidation of the white (but not red) phosphorus — a process now termed chemiluminescence. Together with nitrogen, arsenic, antimony, and bismuth, phosphorus is classified as a pnictogen.

Phosphorus is essential for life. Phosphates (compounds containing the phosphate ion, PO₄³⁻) are a component of DNA, RNA, ATP, and phospholipids. Elemental phosphorus was first isolated from human urine, and bone ash was an important early phosphate source. Phosphate mines contain fossils because phosphate is present in the fossilized deposits of animal remains and excreta. Low phosphate levels are an important limit to growth in some aquatic systems. The vast majority of phosphorus compounds produced are consumed as fertilisers. Phosphate is needed to replace the phosphorus that plants remove from the soil, and its annual demand is rising nearly twice as fast as the growth of the human population. Other applications include organophosphorus compounds in detergents, pesticides, and nerve agents.