Phosphorus (P)
Reactive nonmetal
Phosphorus exists in dramatically different forms: white phosphorus ignites spontaneously in air and glows in the dark, while red phosphorus sits calmly on the striking strip of every matchbox. Life cannot exist without it — it links the backbone of DNA.
Position on the periodic table
Atomic properties
| Atomic number | 15 |
|---|---|
| Atomic mass | 30.9738 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p3 |
| Noble gas shorthand | [Ne] 3s2 3p3 |
| Electrons per shell | 2, 8, 5 |
| Valence electrons (outer shell) | 5 |
| Common oxidation states | -3, +3, +5 |
| Electronegativity (Pauling) | 2.19 |
| Covalent radius (approx.) | 107 pm |
| First ionization energy | 1012 kJ/mol |
| Electron affinity | 72 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 1.823 g/cm³ |
| Melting point | Not available |
| Boiling point | Not available |
| Appearance | colourless, waxy white, yellow, scarlet, red, violet, black |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of phosphorus
Phosphorus's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p3, usually shortened to [Ne] 3s2 3p3. Its electrons occupy 3 shells (2, 8, 5), placing it in period 3 of the p-block. The 5 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of phosphorus
- Fertilisers (phosphates) — its biggest use by far
- Match striking surfaces (red phosphorus)
- Detergents and water softeners
- Steel manufacturing and flame retardants
Biological role: Essential — DNA, RNA, cell membranes, bones and teeth, and the energy molecule ATP all depend on phosphate.
Occurrence: Never found free; mined from phosphate rock.
Common compounds of phosphorus
H3PO4
Phosphoric acid
Ca3(PO4)2
Calcium phosphate
P2O5
Phosphorus pentoxide
History and discovery
Discovered: 1669 — Hennig Brand. Name origin: From Greek phosphoros, “light-bearer”, for its eerie glow.
Discovered in 1669 by Hennig Brand — the first element discovery attributable to a known person.
Safety notes
White phosphorus is highly toxic and ignites in air — strictly a sealed-container substance. Red phosphorus is far safer.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Phosphorus
1. What is the chemical symbol of Phosphorus?
2. What is the atomic number of Phosphorus?
3. Which category does Phosphorus belong to?
4. What is the state of Phosphorus at room temperature?
5. Which period of the periodic table is Phosphorus in?
Phosphorus FAQs
What is the atomic number of phosphorus?
Phosphorus's atomic number is 15 — every phosphorus atom has 15 protons in its nucleus.
What is the symbol for phosphorus?
P. From Greek phosphoros, “light-bearer”, for its eerie glow.
Is phosphorus a metal, nonmetal, or metalloid?
Phosphorus is classified as a reactive nonmetal.
What state is phosphorus at room temperature?
At about 25 °C, phosphorus is a solid.
How many valence electrons does phosphorus have?
Phosphorus has 5 electrons in its outer shell (shell pattern: 2, 8, 5).
What is phosphorus used for?
Key uses include: fertilisers (phosphates) — its biggest use by far; match striking surfaces (red phosphorus); detergents and water softeners.
Related elements
Keep working with this element
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