subject: Characteristics Of Carbon [print this page] Carbon belongs to group 14 of the periodic table. It is the most important constituent of all organic matter. C has atomic number 6 and electronic configuration 1s22s22p2. It has a valency of 4.
Introduction: Characteristics of Carbon
Occurrence: Carbon occurs in the free state in the form of coal, diamond and graphite. In combined form, it occurs as carbon dioxide, carbonates and hydrocarbons.
Allotropic forms of carbon: The phenomenon of existence of a substance in various physical forms but same chemical form is known as 'allotropy'. Carbon exists in three allotropic forms.
(i)Diamond- a hard beautiful crystalline substance.
(ii)Graphite- a soft greyish black crystalline substance.
(iii)Amorphous Carbon-black residue left when carbon compounds are heated. Different varieties of amorphous carbon are a)coal b)coke c)charcoal d)bone black or animal charcoal e)lamp black f)carbon black g)petroleum coke.
Characteristics of Carbon: Diamond and Graphite
Among all the allotropic forms, diamond and graphite are most important.
Characteristics of Diamond:
Diamond: (i)In diamond, each C atom is in sp3hybridised state and is linked to four other neighbouring C atoms held at the corners of a regular tetrahedron by covalent bonds.This results in a very big 3D polymeric structure in which C-C distance is 1.54 A and bond angle is 109.5.
(ii)Diamond is the hardest substance known and possesses abnormally high melting point(about 3600C)
(iii)It is extremely inert chemically.
(iv)Diamond crystals are non conductors of electricity.
Characteristics of Graphite:
Graphite: (i) Here each C atom is in sp2hybridised state and is thus attached to three other C atoms by three s bonds, forming a hexagonal planar structure.The fourth electron present in an unhybridised p orbital of each C atom of a hexagonal unit then overlaps with each other to form ? bnd.Hence the C-C bond length in graphite is shorter (1.42 A) than that in diamond(1.54A).Thus unlike diamond, graphite has a 2D-sheet like character.
(ii)Graphite is a good conductor of electricity.
(iii)Graphite is soft, greasy and has a lubricant character and a low density.
(iv)Graphite is more reactive than diamond due to the presence of a mobile electron on each C -atom.
Characteristics of Carbon: Chemical Properties
1.Burning: All allotropic forms of C burn in air or oxygen to form CO2 (when air supply is sufficient) and CO (when air supply is insufficient)
2.Reducing properties: C is a strong reducing agent and reduces many metallic oxides to metals.
3.Formation of carbides: When heated with certain oxides, it forms the corresponding carbides e.g.
CaO + 3C -------------------> CaC2 + CO
4.Catenation Property:This is the msot important and unique characteristics of carbon.It has the unique capability of bonding with other C atoms to form long chains.C can form single, double or triple bonds with other C atoms.This property leads to the formation of hydrocarbons etc.., and is the basis of a very important branch of science "organic chemistry."
