Phosphorus
Element 15 · Nonmetal
Phosphorus is the element life runs on: it links the backbone of DNA, stores cellular energy in ATP, and hardens bones and teeth as calcium phosphate. It comes in dramatic allotropes — waxy white phosphorus that glows in the dark and ignites spontaneously in air, stable red phosphorus on matchbox strikers, and black phosphorus with layered sheets. Farmers spread millions of tons of phosphate fertilizer yearly, since phosphorus limits plant growth worldwide. Chemically it favors the +5 and +3 oxidation states, forming the phosphate ion at the heart of biochemistry.
Key facts
| Atomic number | 15 |
|---|---|
| Atomic weight | 30.974 |
| Category | Nonmetal |
| Group / Period | 15 / 3 |
| Block | p |
| Electron configuration | 1s2 2s2 2p6 3s2 3p3 |
| Common oxidation states | +5, +3, -3 |
| State at STP | Solid |
| Electronegativity | 2.19 |
| Atomic radius | 98 pm |
| Density | 1.823 g/cm³ |
| Melting point | 44.15 °C (white phosphorus) |
| Boiling point | 280.5 °C (white phosphorus) |
Occurrence
Phosphorus never occurs free; it sits in phosphate rock deposits and in every living cell. Human bones and teeth store it as hydroxyapatite, and the oceans cycle it through marine life.
Applications
Phosphate fertilizers
Matches and pyrotechnics
DNA, ATP, and biochemistry
Detergents (declining use)
Steel treatment
Common compounds
- Phosphoric acid (H3PO4)
- Calcium phosphate (Ca3(PO4)2)
- Adenosine triphosphate (ATP)
- Phosphorus pentoxide (P4O10)
White phosphorus glows greenish in the dark — the eerie light that gave the element its name, 'light-bearer' in Greek.
Data source: IUPAC standard atomic weights 2021