Phosphorus
Phosphorus (P) is a reactive nonmetal with atomic number 15 and an atomic mass of 30.974. Its electron configuration is [Ne] 3s2 3p3, which gives it 5 valence electrons.
Phosphorus key data
| Symbol | P |
|---|---|
| Atomic number | 15 |
| Atomic mass (standard atomic weight) | 30.974 |
| Molar mass | 30.974 g/mol |
| Protons | 15 |
| Neutrons (most abundant isotope, phosphorus-31) | 16 |
| Electrons (neutral atom) | 15 |
| Valence electrons | 5 |
| Category | Reactive nonmetal |
| Period | 3 |
| Group | 15 |
| Block | p-block |
| Noble gas notation | [Ne] 3s2 3p3 |
| Full electron configuration | 1s2 2s2 2p6 3s2 3p3 |
| Electrons per shell | 2, 8, 5 |
Atomic mass: IUPAC CIAAW abridged standard atomic weights, 2024. Most abundant isotope: NIST Atomic Weights and Isotopic Compositions.
The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.
Measured properties of phosphorus
From PubChem, the US National Institutes of Health. Public domain.
| Melting point | 317.3 K (44.15 °C), 86th of 103 by melting point |
|---|---|
| Boiling point | 553.65 K (280.5 °C), 80th of 93 by boiling point |
| Density | 1.82 g/cm³, 79th of 96 by density |
| State at room temperature | Solid |
| Electronegativity | 2.19 (Pauling), 23rd of 95 by electronegativity |
| Van der Waals radius | 180 pm, joint 81st of 99 by atomic radius |
| First ionisation energy | 10.487 eV (1011.8 kJ/mol), 14th of 102 by first ionisation energy |
| Electron affinity | 0.746 eV (72 kJ/mol), joint 30th of 57 by electron affinity |
| Common oxidation states | +5, +3, −3 |
| Discovered | 1669 |
Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.
Phosphorus electron configuration
The full electron configuration of phosphorus is 1s2 2s2 2p6 3s2 3p3. With the noble-gas core collapsed it is [Ne] 3s2 3p3, and the outermost subshell is 3p3.
Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.
Mass of one phosphorus atom
A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.
Mass of one atom
- one atom = 30.974 / (6.02214076 × 10²³)
- = 5.1434 × 10⁻²³ g
Atoms in one gram
- atoms per gram = 6.02214076 × 10²³ / 30.974
- = 1.9443 × 10²² atoms
Phosphorus on the periodic table
Phosphorus is in period 3, group 15, in the p-block.
The other elements of group 15 are nitrogen, arsenic, antimony, bismuth and moscovium.