Reactive nonmetalElement 15 · p-block

Phosphorus (P)

Phosphorus (P) is a reactive nonmetal with atomic number 15 and a standard atomic weight of 30.974. At room temperature it is a solid that melts at 44 °C and boils at 281 °C.

15PPhosphorus30.974

Atomic number

protons

Atomic weight

30.974

CIAAW 2024

Melting point

44 °C

white phosphorus

Boiling point

281 °C

553.7 K

Density

1.823 g/cm³

near room temperature

Electronegativity

2.19

Pauling scale

State at 25 °C

Solid

Discovered

1669

Germany

Phosphorus at a glance

Identity

Symbol	P
Atomic number (Z)	15
Atomic weight	30.974 ± 0.001 (CIAAW 2024)
Category	Reactive nonmetal
Group	15 — pnictogens (nitrogen group)
Period	3
Block	p-block
CAS number	7723-14-0

Atomic properties

Electron configuration	[Ne] 3s² 3p³ Full: 1s² 2s² 2p⁶ 3s² 3p³
Electrons per shell	2, 8, 5
Oxidation states	-3, +3, +5 Less common: -2, -1, 0, +1, +2, +4
Electronegativity (Pauling)	2.19
First ionisation energy	10.487 eV (1,011.8 kJ/mol) 2nd: 19.77 eV · 3rd: 30.203 eV
Electron affinity	0.747 eV
Atomic radius (empirical)	100 pm
Covalent radius	111 pm
Van der Waals radius	180 pm

Physical properties

State at 25 °C	Solid
Melting point	44.15 °C · 111.5 °F · 317.3 K white phosphorus
Boiling point	280.6 °C · 537 °F · 553.7 K
Density	1.823 g/cm³
Specific heat capacity	0.769 J/(g·K)
Crystal structure	Cubic

Isotopes & abundance

Natural occurrence	Primordial
Radioactive	No
Natural isotopes (abundance)	³¹P 100%
Stable isotopes	3
Known isotopes	24
Abundance in Earth's crust	1,050 mg/kg
Abundance in seawater	0.06 mg/L

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Phosphorus electron configuration

Phosphorus has 15 electrons. Written in short form, its ground-state configuration is [Ne] 3s² 3p³ — the electrons of the noble gas neon, plus 3s² 3p³.Written out in full: 1s² 2s² 2p⁶ 3s² 3p³.

As a member of group 15 it has 5 valence electrons in its outer shell (shell 3), which largely decide its chemistry.

3s↑↓

3p↑↑↑

Discovery and name

Discovered

1669 — Hennig Brand · Germany.

Name

Greek phōsphoros, light-bearing — white phosphorus glows in air.

Known for

Essential for life — it is in DNA, ATP and bones. Mined phosphate rock goes mainly into fertilisers; red phosphorus is on matchbox strikers.

Isotopes of phosphorus

Naturally occurring phosphorus is a mix of 1 isotope. Each has 15 protons; they differ in the number of neutrons:

Isotope	Protons	Neutrons	Natural abundance	Stability
³¹P	15	16	100%	stable

24 isotopes of phosphorus are known in our data set (half-lives as published in nuclear data tables).

Phosphorus compared with group 15

The other elements in group 15 (pnictogens (nitrogen group)), from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Nitrogen	7	14.007	-210 °C	-196 °C	1.2506 g/L	3.04
Phosphorus	15	30.974	44 °C	281 °C	1.823 g/cm³	2.19
Arsenic	33	74.922	—	614 °C	5.75 g/cm³	2.18
Antimony	51	121.76	631 °C	1,587 °C	6.68 g/cm³	2.05
Bismuth	83	208.98	271 °C	1,564 °C	9.79 g/cm³	2.02
Moscovium	115	[290]	—	—	13.5 g/cm³ (pred.)	—

Frequently asked questions

6 answers

What is the atomic mass of phosphorus?

The standard atomic weight of phosphorus is 30.974 ± 0.001 (CIAAW 2024), so one mole weighs about 30.974 grams.

How many protons, neutrons and electrons does phosphorus have?

A neutral phosphorus atom has 15 protons and 15 electrons. Its most common isotope, phosphorus-31, has 16 neutrons.

What is the electron configuration of phosphorus?

[Ne] 3s² 3p³ (in full: 1s² 2s² 2p⁶ 3s² 3p³).

What are the melting and boiling points of phosphorus?

Phosphorus melts at 44.15 °C (111.5 °F) and boils at 280.55 °C (537 °F).

Is phosphorus a metal?

Phosphorus is a nonmetal. It is in group 15, period 3, and is a solid at room temperature.

Who discovered phosphorus?

1669 — Hennig Brand (Germany).