Chemical element · reference page

15P

Phosphorus

Phosphorus is element 15 (P), located in period 3, group 15 and the p block. At room temperature its reference phase is solid. Its electron configuration is [Ne] 3s2 3p3.

Atomic number15

Standard atomic weight30.973761998(5)

Group15

Period3

Blockp

Electron configuration[Ne] 3s2 3p3

Electronic structure

What controls its chemistry

Group 15 atoms have five valence electrons. They can form three covalent bonds, participate in multiple bonding, or adopt several oxidation states depending on the element and its bonding partners.

The configuration [Ne] 3s2 3p3 places phosphorus in this family, but the chemistry changes markedly from non-metallic nitrogen and phosphorus to the heavier, more metallic members.

Chemical forms

Compounds, ions and materials

Common families include hydrides, oxides, oxoacids or oxoanions, halides and compounds with metals. Oxidation states from −3 to positive values occur across the group, with the accessible range changing strongly from nitrogen to bismuth.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 1.823 g/cm³. Where a phase-transition value is not listed, the behaviour may be poorly defined under ordinary pressure, depend strongly on allotrope, or lack a reliable reference value. Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where phosphorus is found and used

In practice, phosphorus is encountered in fertiliser production, biology and matches.

In practice

Examples of real uses

Fertiliser production

Phosphorus is part of fertiliser chemistry or the industrial processes used to supply essential plant nutrients.

Biology

Phosphorus ions or compounds participate in biological structures, enzymes, signalling or metabolism.

Matches

Phosphorus chemistry is used in match ignition systems, especially in the striking surface of safety matches.

Periodic position

What its neighbours tell us

Phosphorus is in period 3 and group 15. In the neighbourhood shown here, it lies between silicon and sulfur in the same period; nitrogen is above it and arsenic below it in the same group. These positions make it possible to compare atomic size, ionisation energy and bonding behaviour with nearby elements.

Reference data

Physical and atomic properties

Classificationpolyatomic nonmetal

Phase at room temperatureSolid

Electron shells2 · 8 · 5

Density1.823 g/cm³

Melting point—

Boiling point—

Pauling electronegativity2.19

First ionisation energy1 012 kJ/mol

Electron affinity72.04 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of phosphorus is associated with Hennig Brand. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 30.973761998(5). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Phosphorus has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with phosphorus depend on chemical form, dose and route of exposure. Pure phosphorus, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.