Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen.
The most common oxidation state of carbon in inorganic compounds is 4, while 2 is found in carbon monoxide and transition metal carbonyl complexes.
The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil, and methane clathrates.
For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F).
Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such as tungsten or rhenium.
It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.
The physical properties of carbon vary widely with the allotropic form.
Its first four ionisation energies, 1086.5, 2352.6, 4620..7 k J/mol, are much higher than those of the heavier group 14 elements.
The electronegativity of carbon is 2.5, significantly higher than the heavier group 14 elements (1.8–1.9), but close to most of the nearby nonmetals as well as some of the second- and third-row transition metals.
Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars.
Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions.
At elevated temperatures, carbon reacts with oxygen to form carbon oxides, and will rob oxygen from metal oxides to leave the elemental metal.