Carbon

At a glance

Symbol

C

Atomic number

6

Average atomic mass

12.01

Group

14

Period

2

Family

nonmetal

Electron configuration

1s² 2s² 2p², or [He] 2s² 2p²

Valence electrons

4

Electronegativity

2.55

Common ions

shares electrons in covalent bonds; C⁴⁻ in a few carbides

Isotopes

¹²C (98.9%) and ¹³C (1.1%); radioactive ¹⁴C, made in the upper atmosphere, is used for radiocarbon dating

On the table

Period 2, group 14. The other nonmetals are tinted, and every cell opens its own article.

Electrons and bonding

Four valence electrons, halfway to a full shell, so carbon shares electrons instead of gaining or losing them. It forms four covalent bonds, including to other carbon atoms in chains, rings, and double and triple bonds.

Properties

State at 25 °C

solid

What it looks like

soft, black graphite or clear, very hard diamond, depending on how the atoms are arranged

Sublimes

at about 3642 °C, going straight from solid to gas

Density

2.27 g/cm³ for graphite, 3.51 g/cm³ for diamond

Where it is found

About 0.02% of the crust by mass, mostly locked in limestone, chalk and marble as carbonates. It is in coal, oil and natural gas, in the air as carbon dioxide, and in every living thing: about 18% of your body by mass. Diamond and graphite also occur naturally.

Discovery and name

Known since prehistory as charcoal and soot. Antoine Lavoisier listed it as an element in 1789, and in 1797 Smithson Tennant showed that burning diamond gives nothing but carbon dioxide. The name comes from the Latin carbo, charcoal. A third form, the soccer-ball-shaped C₆₀ molecule, was discovered in 1985.