|Atomic mass||12 amu|
|Date of discovery||Carbon has been known since ancient times.|
|Name of discoverer||Unknown|
|Name origin||From the Latin carbo.|
|Obtained from||Incomplete combustion.|
Carbon is the sixth element in the periodic table of the elements. Its bonding structure, which is extremely conducive to the formation of polymers, along with its relative abundance and stability, make it integral to the formation of life on Earth.
Carbon and Living Matter
The predominance of carbon in living matter is no doubt a result of its tremendous chemical versatility compared with other elements. Carbon has the unique ability to form a virtually infinite number of compounds as a result of its capacity to make as many as four highly stable covalent bonds combined with its ability to form covalently lined carbon carbon chains of unlimited extent. Thus, of the over 13 million chemical compounds that are presently known, nearly 90% are organic substances.
Only five elements, Boron, Carbon, Nitrogen, Silicon, and Phosphorus, have the capacity to make three or more bonds each and thus to form chains of covalently linked atoms that can also have pendant side chains. The other elements are either metals, which tend to form ions rather than covalent bonds; noble gases, which are essentially chemically inert; or atoms such as Hydrogen or Oxygen that can each make only one or two covalent bonds.
Although B, N, Si, and P can each participate in at least three covalent bonds, they are unsuitable as a basis of complex chemistry. Boron, having fewer valence electrons (three) than valence orbitals (four), is electron deficient. This severely limits the types of stabilities of compounds that B can form. Nitrogen has the opposite problem; its five valence electrons make it electron rich. The repulsions between the lone pairs of electrons on covalently bonded N atoms serve to greatly reduce the bond energy of a Nitrogen Nitrogen bond relative to the unusually stable triple bond of the N2 molecule. Even short chains of covalently bonded N atoms therefore tend to decompose, usually violently, to N2. Silicon and carbon, being in the same column of the periodic table, might be expected to have similar chemistries. Silicon's large atomic radius, however, prevents two SI atoms from approaching each other closely enough to gain much orbital overlap. Consequently Si Si bonds are weak and the corresponding multiple bonds are rarely stable. Si O bonds, in contrast are so stable that chains of alternating Si and O atoms are essentially inert. Phosphorus, being below N in the periodic table, forms even less stable chains of covalently bonded atoms.
Allotropes of Carbon
Carbon, with its ability to form different types of bonds, forms several allotropes -
- Biochemistry 2ed Voet & Voet