Carbon

Carbon (chemical symbol C) is one of the basic organic elements, and is a fundamental constituent of all organic molecules - and therefore all terrestrial life. Its unique versatility in forming different compounds comes from its ability to form multiple atomic bonds with itself.

Chemistry

Physical chemistry

Carbon is an element of the IV group of the periodic table of Dmitrij Ivanovič Mendeleev; has in its fundamental state, the following configuration electronics: [He]2s² 2p² (two unpaired electrons therefore, in two of the three 2p isoenergetic orbitals). Its oxidation number varies from + 4 to – 4. It can undergo hybridization: sp³ (four degenerate hybrid orbitals oriented to vertices of a regular tetrahedron), sp² (three degenerate hybrid orbitals arranged on a plane passing through the nucleus of the atom oriented towards the vertices of an equilateral triangle) or sp (two degenerate hybrid orbitals arranged spatially along a straight line passing through the nucleus of the atom, at 180° from each other) ⁸.

Carbon is a non-metallic solid, which in its common pure graphite form forms a black flaky substance. It has an atomic number 6 with a relative atomic weight of 12.011. It has a melting point of 3527°C and a boiling point of 4027°C ^1,2.

Carbon exists in multiple different allotropes or physical forms, in fact the most of any element. Historically, diamond and graphite were the two known allotropes. Now there are many more including graphene, nanotubes, buckminsterfullerene and many others ¹.

Carbon forms an incredible number of compounds, indeed more than those of all the other elements combined, because of its unique ability to form bonds with itself ¹.

Radiochemistry

The vast majority (>98%) of carbon found on earth comprises the stable isotope carbon-12. Most of the rest of the terrestrial carbon exists as carbon-13. Carbon-14 exists in tiny amounts and is of vital importance in so-called carbon dating. Twelve other radioisotopes of carbon are known to exist, from carbon-8 to carbon-22 ².

Toxicity

Carbon in its pure state is not generally thought of as toxic, indeed when children have swallowed pencils or pencil lead virtually no associated toxicity occurs. However, this is not true for other forms of carbon. Black carbon, a distinct form of carbon produced by the incomplete combustion of fossil fuels and an important component of air pollution is toxic ³. The toxicity of allotropic forms of carbon such as nanotubes and graphene is an active area of research and of some concern in view of the planned introduction of these materials into the environment ^6,7.

Radiological importance

Carbon-11 has been used to label a wide variety of compounds for conventional nuclear medicine and PET studies. However its usefulness is limited due to its short half-life of approximately 20 minutes which means it can only be used in centers with a cyclotron ⁴.

History and etymology

Carbon has been known about since antiquity ¹.

The word carbon ultimately derives from the Latin word “carbo” meaning coal ⁵.