Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[He] 2s² 2p²
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 4
Number of electrons in each shell, from the nucleus outwards.
4,489 °C (4,762 K), only under pressure
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
3,825 °C (4,098 K), sublimes
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
2.267 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.55 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
11.26 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
1.262 eV
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
76 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+4, +2, -4
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Carbon (C) is a chemical element with atomic number 6. It sits in group 14 and period 2 of the periodic table, in the p-block. It is a nonmetal. At room temperature it is a solid. Its standard atomic weight is 12.011.
Origin of the name
The name comes from Latin carbo, ‘charcoal, coal’: soot and charcoal were the forms of carbon known since prehistory. Antoine Lavoisier coined the French carbone, and English took it over. German calls it Kohlenstoff, ‘coal substance’.
Where is carbon found?
Carbon is found in the Sun and stars, in comets and in the atmospheres of most planets. On Earth most of it lies in carbonate rocks such as limestone and dolomite, and in coal, oil and natural gas; the air holds it as carbon dioxide, which also dissolves in water. Pure carbon occurs as graphite and diamond. All living things are built of carbon compounds.
What is carbon used for?
Most carbon is burned as fuel: coal, oil and natural gas. Coke, made from coal, turns iron ore into iron and steel. Graphite mixed with clay is the “lead” of pencils, and it also serves as a lubricant. Diamonds cut, drill and grind hard materials; most industrial diamonds are made artificially. Carbon black, a fine soot, colours tyres and printing inks.
Interesting facts
Graphite is one of the softest materials and diamond one of the hardest, yet both are pure carbon: only the arrangement of the atoms differs.
In 1772 Antoine Lavoisier burned a diamond and got carbon dioxide; in 1797 Smithson Tennant proved that diamond is pure carbon.
Carbon forms millions of compounds, more than any other element; their study is a whole branch of science, organic chemistry.
Radioactive carbon-14 has a half-life of about 5,700 years, which is used to date wood, bones and other remains of living things.