Phosphorus
[Ne] 3s² 3p³ · 2 · 8 · 5
The element without which there is no DNA, no ATP and no bone. White phosphorus glows in the dark and ignites in air; red phosphorus is safe and sits on the side of a matchbox — one element in two utterly different guises.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 15
- Atomic mass
- 30.974 а.е.м.
- Electron configuration
- [Ne] 3s² 3p³
- Electrons per shell
- 2 · 8 · 5
- Block
- p-block
- Group
- Pnictogens
- Period
- 3
- Electronegativity (Pauling)
- 2.19
- Electronegativity (Allen)
- 2.25
- Atomic radius
- 98 pm
- Covalent radius
- 107 pm
- Van der Waals radius
- 180 pm
- Ionisation energy 1
- 1 011.8 kJ/mol
- Ionisation energy 2
- 1 907 kJ/mol
- Ionisation energy 3
- 2 914.1 kJ/mol
- Ionisation energy 4
- 4 963.6 kJ/mol
- Ionisation energy 5
- 6 273.9 kJ/mol
- Electron affinity
- 72 kJ/mol
- Common oxidation states
- -3, +3, +5
- Oxidation states
- -3, -2, -1, +1, +2, +3, +4, +5
Physical properties
- State at 25 °C
- solid
- Density
- 1.823 g/cm³
- Melting point
- 317.3 K · 44.2 °C
- Boiling point
- 553.7 K · 280.6 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 0.66 kJ/mol
- Heat of vaporisation
- 12.4 kJ/mol
- Specific heat capacity
- 0.769 J/(g·K)
- Thermal conductivity
- 0.236 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- 11 GPa
- Poisson ratio
- no data
- Mohs hardness
- 0.5
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 1·10⁹ nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- triclinic
- Lattice constants
- a = 1 145 pm · b = 550.3 pm · c = 1 126.1 pm
Abundance
- In the crust
- 1 050 mg/kg
- In the ocean
- 0.06 mg/L
- In the universe
- 7 000 mg/kg
- In the human body
- 11 000 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 31P | 100 % | stable | — |
| 32P | — | 14.27 d | β− |
Phosphorus-31 is the only stable isotope, which is why ³¹P NMR can watch energy metabolism in living tissue inside a scanner.
Discovery
- Year of discovery
- 1669
- Discovered by
- Hennig Brand
- Where
- Germany
- Origin of the name
- from Greek phosphoros (light-bearer): white phosphorus glows in the dark
History
Hennig Brand boiled down urine in 1669 looking for the philosopher's stone and got a substance that glowed in the dark. It is the first element discovered in a documented experiment rather than known from antiquity.
Where it occurs
1050 mg/kg of the crust, almost all as phosphate. The industrial ores are apatite and phosphorite; the largest reserves are in Morocco and Western Sahara.
How it is produced
Phosphate rock is either digested with sulfuric acid into phosphoric acid, or reduced in an electric furnace with coke and silica to white phosphorus.
Role in living things
Phosphate is the backbone of DNA and the currency of energy as ATP. In bone it is locked into hydroxyapatite; phosphorus is about 1 % of body mass.
Safety
White phosphorus is severely toxic and causes deep burns that heal badly. In the nineteenth century match workers suffered phosphorus necrosis of the jaw, after which white phosphorus was banned from matches.
Uses
- Phosphate fertiliser — over 80 % of all phosphorus mined
- Detergents, food additives and feed phosphates
- Lithium iron phosphate batteries
- Matches, incendiary and smoke compositions
- Doping semiconductors to make them n-type
Curiosities
- The name means light-bearer: white phosphorus oxidises slowly in air and glows faintly.
- Phosphate rock reserves are finite and phosphorus has no substitute in fertiliser — one of the century's sharper resource risks.
- In a matchbox the phosphorus is on the striking strip, not on the match.
- Phosphorus is the one element whose discoverer kept the method secret and sold it as such.