Carbon (C)

Carbon forms more compounds than every other element combined — millions of them — because it bonds to itself in chains, rings and sheets without the bonds getting weaker. Its allotropes are the widest spread of properties any single element manages: diamond is the hardest natural substance and one of the best thermal conductors, graphite is soft enough to write with, and both are pure carbon differing only in how the atoms are arranged. Carbon-14, made continuously in the upper atmosphere by cosmic rays, decays with a half-life of 5,730 years, which is what makes radiocarbon dating work back to roughly 50,000 years.

Properties

Atomic number

6

Symbol

C

Standard atomic weight

12.011 u

Category

Nonmetal

Group

14

Period

2

Block

p-block

Electron configuration

[He] 2s² 2p²

Electrons per shell

2, 4

Melting point

3,823 K — 3549.8 °C — 6421.7 °F

Boiling point

4,098 K — 3824.8 °C — 6916.7 °F

Density

2.267 g/cm³

Electronegativity

2.55 (Pauling)

Oxidation states

+4, +2, -4

Discovered

Known since antiquity

Electron configuration

Full

1s² 2s² 2p²

Noble gas shorthand

[He] 2s² 2p²

Shells

K: 2 · L: 4

What it is used for

• Steelmaking — carbon content is what separates iron from steel
• Graphite electrodes in electric arc furnaces and in lithium-ion anodes
• Carbon fibre in bicycles, aircraft and wind turbine blades
• Activated charcoal in water filters and in emergency medicine
• Diamond abrasives and cutting tools

IUPAC publishes an interval, [12.0096, 12.0116]; 12.011 is the conventional value. Carbon does not melt at ordinary pressure — graphite sublimes near 3,900 K — and the quoted melting point applies under roughly 10 MPa. The density given is for graphite; diamond is 3.51 g/cm³.

Neighbours in the table

Group 14

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Carbon sits in group 14 with silicon, germanium, tin, lead, flerovium.