Phosphorus (P)
Element 15 · Nonmetal · atomic mass 30.974 u · group 15, period 3
Electron shells: 2, 8, 5
Phosphorus is essential to life — it forms the backbone of DNA and the energy currency ATP. White phosphorus ignites spontaneously in air, while the red form is stable enough for matchboxes.
It was discovered in 1669 by boiling down large quantities of human urine.
- Atomic number
- 15
- Atomic mass
- 30.974 u
- Electron configuration
- [Ne] 3s² 3p³
- Group · period · block
- 15 · 3 · p
- Oxidation states
- −3, +3, +5
- Electronegativity
- 2.19 (Pauling)
- Melting point
- 44.15 °C
- Boiling point
- 281 °C
- Density
- 1.82 g/cm³
- State at 20 °C
- Solid
- Appearance
- Waxy white, red or black solid
- Discovered
- Hennig Brand, 1669
15 protons, and 15 electrons when neutral
IUPAC standard atomic weight
Pnictogens
What Phosphorus is used for
- Fertilisers
- Match heads and strikers
- Detergents and water treatment
- Steel and bronze alloying
Atomic structure of Phosphorus
A neutral phosphorus atom has 15 protons and 15 electrons. Its most common isotope carries about 16 neutrons, which is where the mass number 31 comes from. Change the neutron count and you have a different isotope of phosphorus; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 5. In orbital notation that is [Ne] 3s² 3p³, leaving 5 valence electrons in the outer shell — the ones that do the chemistry.
3D electron orbitals
See where Phosphorus's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Phosphorus sits in the periodic table
Poor conductors that gain or share electrons rather than losing them. They make up almost all the mass of living things.
Discovery and naming
Phosphorus was discovered by Hennig Brand in 1669. Its name comes from Greek phosphoros, "light-bearer".
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Phosphorus?
The standard atomic weight of Phosphorus is 30.974 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Phosphorus have?
Phosphorus has 15 protons, because the atomic number is the proton count and that is what makes an atom Phosphorus at all. A neutral Phosphorus atom has the same number of electrons, 15. The neutron count varies by isotope; the most common one has about 16, since 31 − 15 = 16.
What is the electron configuration of Phosphorus?
The electron configuration of Phosphorus is [Ne] 3s² 3p³. Its electrons are arranged 2, 8, 5 across 3 shells.
Is Phosphorus a metal?
No. Phosphorus is classified as a nonmetal, on the right-hand side of the table where elements gain or share electrons rather than losing them.
What group and period is Phosphorus in?
Phosphorus is in group 15 (the pnictogens), period 3, in the p-block. The group is its column and the period is its row.
What is the charge of Phosphorus?
Phosphorus most commonly forms a 3− ion. It is 3 electrons short of a full outer shell, so it gains them rather than losing 5. Across all its compounds it shows oxidation states of −3, +3, +5.
What is the melting point of Phosphorus?
Phosphorus melts at 44.15 °C and boils at 281 °C. That puts it in the solids at everyday temperatures.
What is Phosphorus used for?
Fertilisers, Match heads and strikers, Detergents and water treatment, Steel and bronze alloying. Phosphorus is essential to life — it forms the backbone of DNA and the energy currency ATP.
Who discovered Phosphorus, and where does its name come from?
Phosphorus (P) was discovered by Hennig Brand in 1669. The name comes from Greek phosphoros, "light-bearer".