ElementsWhat is phosphorus?
Phosphorus has several forms. White phosphorus is waxy, poisonous and catches fire in air. Red phosphorus is much safer. Bones, teeth and DNA all contain phosphorus.
What is phosphorus used for?
Fertilisers above all. Also the striking strip on matchboxes, detergents, and steel making.
Where the name comes from
From the Greek word phosphoros, 'light bearer', because white phosphorus glows in the dark.
Key facts
- Symbol
- P
- Atomic number
- 15
- Atomic mass
- 30.97376200 u
- Family
- Nonmetal
- Period
- 3
- Group
- 15
- Block
- p
- State at room temperature
- Solid
- Melting point
- 44.2 °C (317.3 K, 111 °F)
- Boiling point
- 280.5 °C (553.65 K, 537 °F)
- Density
- 1.82 g/cm³
- Electrons per shell
- 2, 8, 5
- Electron configuration
- [Ne]3s2 3p3
- Common oxidation states
- +5, +3, -3
- Electronegativity (Pauling)
- 2.19
- First ionisation energy
- 10.487 eV
- Electron affinity
- 0.746 eV
- Atomic radius (van der Waals)
- 180 pm
- Discovered
- 1669
Place in the periodic table
Phosphorus is element number 15. It sits in period 3 (row 3) of the periodic table, in group 15 (column 15), and belongs to the p-block. Just before it comes silicon (14), and just after it comes sulfur (16). In the same column, nitrogen is above it and arsenic is below it. Elements in one column tend to behave alike.
Family: Nonmetals.
Physical properties
At room temperature phosphorus is a solid. It melts at 44.2 °C and boils at 280.5 °C, so it stays liquid over a range of 236 degrees. Its density is 1.82 grams per cubic centimetre, so a one-litre block would weigh about 1.82 kilograms. By density it ranks 79th among the 96 elements with a measured value.
Inside the atom
An atom of phosphorus has 15 protons in its nucleus and, when neutral, 15 electrons around it. The electrons are arranged in 3 shells: 2, 8, 5. The outermost shell holds 5 electrons. Written in full, the electron configuration is [Ne]3s2 3p3.
Its electronegativity on the Pauling scale is 2.19. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 10.487 electronvolts (about 1,012 kilojoules per mole). One mole of phosphorus weighs 30.97376200 grams, so a single gram contains about 1.94 × 1022 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains phosphorus with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.