Phosphorus

Phosphorus has the chemical symbol P, and its atomic number is 15. Its mass number is 30.97. It is not found in nature as an element, but as compounds, such as phosphates. There are many different forms. The most common form is a red or white waxy solid.

Phosphorus,  ₁₅P

Forms of phosphorus Waxy white Light red Dark red and violet Black waxy white (yellow cut), red (granules centre left, chunk centre right), and violet phosphorus
General properties
Pronunciation	/ˈfɒsfərəs/ ​(FOS-fər-əs)
Appearance	white, red and violet are waxy, black is metallic-looking
Standard atomic weight (Ar, standard)	30.973761998(5)
Abundance
in the Earth's crust	5.2 (silicon = 100)
Phosphorus in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson N ↑ P ↓ As silicon ← phosphorus → sulfur
Atomic number (Z)	15
Group	group n/a
Period	period {{{period}}}
Block	[[{{{block}}}-block]]
Electron configuration	[Ne] 3s2 3p3
Electrons per shell	2, 8, 5
Physical properties
Phase at STP	P: Solid
Melting point	white: 317.3 K ​(44.15 °C, ​111.5 °F) red: ∼860 K (∼590 °C, ∼1090 °F)
Boiling point	white: 553.7 K ​(280.5 °C, ​536.9 °F)
Sublimation point	red: ≈689.2–863 K ​(≈416–590 °C, ​≈780.8–1094 °F) violet: 893 K (620 °C, 1148 °F)
Density (near r.t.)	white: 1.823 g/cm3 red: ≈2.2–2.34 g/cm3 violet: 2.36 g/cm3 black: 2.69 g/cm3
Heat of fusion	white: 0.66 kJ/mol
Heat of vaporization	white: 51.9 kJ/mol
Molar heat capacity	white: 23.824 J/(mol·K)
Vapor pressure (white) P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 279 307 342 388 453 549
vapor pressure (red, b.p. 431 °C) P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 455 489 529 576 635 704
Atomic properties
Oxidation states	−3, −2, −1, +1, +2, +3, +4, +5 (a mildly acidic oxide)
Electronegativity	Pauling scale: 2.19
Ionization 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 of phosphorus
Other properties
Natural occurrence	P: Primordial
Crystal structure	​body-centered 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)
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct

Red phosphorus in a tube.

White, red, violet, and black phosphorus

Physical properties

Phosphorus comes in several forms. White and red phosphorus are the most common forms. White phosphorus is a waxy white solid. When pure, it is colourless. It is insoluble in water, but soluble in carbon disulfide, an organic solvent. It turns light yellow when in air. It glows in the dark because it "burns" very slowly in air.

When exposed to sunlight, or when heated in its own vapour to 250 °C, it is converted to the red variety. This form does not ignite spontaneously and it is less toxic and less flammable than white phosphorus. The red modification is fairly stable and sublimes with a vapor pressure of 1 atmosphere at 417 °C.

Chemical properties

White phosphorus is more reactive than red phosphorus. White phosphorus catches fire spontaneously in air, burning to make smoke of phosphorus(V) oxide. If it burns in a little air, it produces poisonous phosphorus(III) oxide. When white phosphorus is heated in an alkali, it disproportionates to produce hypophosphites and phosphine. Red phosphorus can burn but needs to be ignited. Phosphorus reacts with the halogens to make phosphorus halides. It reacts with some metals to make phosphides.

Chemical compounds

Phosphorus compounds are chemical compounds containing phosphorus. They are listed below with some of their properties. Phosphorus comes in several oxidation states, the number of electrons moved during a redox reaction. -3 is flammable, powerful reducing agent, and toxic; +1 is a strong reducing agent and is rare; +3 is a weaker reducing agent that is poisonous; +5 is not a reducing agent and is very common.

Phosphides

• Phosphine, toxic gas that smells like fish and ignites by itself
• Phosphide, the ion
• Sodium phosphide

Other compounds

• Phosphorus(V) oxide, phosphorus pentoxide, absorbs water
• Phosphorus(V) chloride

• 

  Phosphoric acid

• 

  Trisodium phosphate

• 

  Phosphorus pentachloride (left) and phosphorus trichloride (right)

In +1 oxidation state

• Hypophosphorous acid, salts are called hypophosphites
• Sodium hypophosphite

Phosphites

• Phosphorous acid, poisonous, salts are called phosphites
• Sodium phosphite

Phosphates

• Phosphoric acid, most common, salts are called phosphates
• Calcium phosphate
• Dicalcium phosphate
• Monocalcium phosphate
• Sodium phosphate
• Zinc phosphate

Occurrence

It is an essential component of living systems and is found as phosphate in nervous tissue, bones and cell protoplasm. It is also found in the earth as phosphate rock. Phosphate rock is the main source of phosphorus and phosphorus compounds. Many body tissues have calcium phosphates in them.

Preparation

Phosphorus was first made by heating a mixture of phosphates and carbon in an iron pot. The phosphates were made by dissolving bones in strong acids and evaporating the solution.

Phosphorus is made now by heating calcium phosphate, carbon, and silicon dioxide in an electric arc furnace. The heat of the electric arc melts the mixture of materials, and phosphorus gas is given off. It is absorbed under water. This makes white phosphorus.

As an element

White phosphorus is used in incendiary weapons and smoke grenades. It is also used to make organic compounds that have phosphorus in them. Phosphorus is used to dope semiconductors. Phosphorus is used to remove oxygen from copper. It is also used in making alloys. Red phosphorus is used in matches and flares.

As chemical compounds

Phosphorus compounds are used for fertilizers, soft drinks, toothpaste, and detergents. Most of these are phosphates. Phosphides can be used to kill rodents.

Safety

White phosphorus is very dangerous. It is very toxic and ignites easily, burning with a very hot flame. Red phosphorus is much safer. Some phosphorus compounds are toxic, but the common phosphates are not toxic.

Phosphorus Media

• 

  The Alchemist in Search of the Philosophers Stone (1771), by Joseph Wright, depicting Hennig Brand discovering phosphorus.

• 

  Guano mining in the Central Chincha Islands, c. 1860

• 

  Matches from 1828. The sulfur-tipped match is dipped into liquid containing white phosphorus, and ignites as it is pulled out of the bottle.

• 

  A worker tends an electric phosphate smelting furnace in Muscle Shoals, Alabama, 1942

• 

  White phosphorus shell explosion in France during the First World War (1918)

• 

  White phosphorus exposed to air glows in the dark.

• 

  The tetrahedral structure of P
  4O
  10 and P
  4S
  10

• 

  A stable diphosphene, a derivative of phosphorus(I)

• 

  Mining of phosphate rock in Nauru

• 

  A phosphate train on its way to the port of Casablanca in Morocco.

Related pages

• Periodic table
• List of common elements