Chemical element · reference page

Carbon

Carbon is element 6 (C), located in period 2, group 14 and the p block. At room temperature its reference phase is solid. Its electron configuration is [He] 2s2 2p2.

Atomic number6

Standard atomic weight[12.0096, 12.0116]

Group14

Period2

Blockp

Electron configuration[He] 2s2 2p2

Electronic structure

What controls its chemistry

Group 14 elements have four valence electrons. That makes covalent bonding especially important for the lighter members, while metallic character increases down the group.

For carbon, the electron configuration [He] 2s2 2p2 sets the number and energy of the valence electrons that participate in bonding. Structure and oxidation state then determine the properties of its materials and compounds.

Chemical forms

Compounds, ions and materials

Elemental carbon occurs in allotropes including graphite and diamond, with graphene representing a single graphite-like sheet. In compounds, carbon forms C–C chains and rings, multiple bonds, carbonates, carbon dioxide, hydrocarbons and the molecular frameworks of biochemistry.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 1.821 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 carbon is found and used

In practice, carbon is encountered in living molecules, graphite, diamond and composite materials.

In practice

Examples of real uses

Living molecules

Carbon forms the molecular skeletons of proteins, carbohydrates, lipids, nucleic acids and many other biological compounds.

Graphite

Graphitic carbon is used where electrical conduction, lubrication or heat resistance is required.

Diamond

Diamond is used as an abrasive and cutting material because its three-dimensional covalent network is exceptionally hard.

Composite materials

Carbon is used in composites to combine low mass with stiffness, strength, heat resistance or other targeted properties.

Periodic position

What its neighbours tell us

Carbon is in period 2 and group 14. In the neighbourhood shown here, it lies between boron and nitrogen in the same period; silicon is directly 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 · 4

Density1.821 g/cm³

Melting point—

Boiling point—

Pauling electronegativity2.55

First ionisation energy1 086 kJ/mol

Electron affinity121.8 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

Carbon or its materials were known in antiquity, long before atomic theory. The modern element is defined by atomic number 6, which distinguishes it unambiguously from compounds and mixtures known to early craftspeople.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is given as the interval [12.0096, 12.0116]. Natural samples can differ slightly in isotope proportions, so a single universal decimal value would hide real variation between materials.

Carbon 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 carbon depend on chemical form, dose and route of exposure. Pure carbon, 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.