Substance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Click on Term to Read More commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. One of the naturally occurring forms of carbon found in meteorites. Each C atom is bonded through covalent sp3 hydrid orbitals to four others. The strength of the C-C bonds makes diamond the hardest naturally occurring substance (according to the Mohs scale) in terms of resistance to scratching. There are Click on Term to Read More*; b. Opaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have Click on Term to Read More*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. Material without the regular, ordered structure of crystalline solids. Amorphous substances, like glass, lack a definite repeating pattern in their atomic structures (crystallinity). There may be small regions of order, but, overall there is disorder. Click on Term to Read More carbon; h. carbon nanotube*.
Carbon has two stable, naturally-occurring isotopes: carbon-12, or 12C, (98.89%) and carbon-13, or 13C, (1.11%), and one unstable, naturally-occurring, radioisotope, 14C (t½ = 5730 y). Variations in carbon isotopic ratio, 13C/12C, are common and often large. They are expressed as d13C (in parts per thousand ‰) relative to the Peedee Belemnite standard (PDB). This material has a higher 13C/12C ratio than nearly all other natural C-based substances and, for convenience, is assigned d13C value of zero. This means that almost all other naturally-occurring samples have negative d13C values.
A basic phase diagram of carbon, which shows the state of matter for varying temperatures and pressures, is shown below. The hashed regions indicate conditions under which one phase is metastable, so that two phases can coexist.
Some or all content above used with permission from J. H. Wittke.