Why are carbon and its compounds so important or special from compounds of all the other more than hundred – odd elements of the periodic table?
This is because –
(a) The number of compounds that contain carbon is many time greater (due to catenation) than the number of compounds that do not contain carbon.
(b) Their molecules can be very large and complex (due to tetracovalency of carbon and tendency to form multiple bonds).
(c) The complex molecules of carbon compounds can rearrange (isomerism), break apart or form into new molecules.
(d) New atoms can be added or substituted the old ones. By the way, a new combination of molecules can be formed. Carbon also forms bonds with other elements such as halogens, oxygen, nitrogen and sulphur by replacing one or more hydrogen from a hydrocarbon chain.
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Further, the versatile nature of carbon can be understood by following main properties –
(1) Catenation – (bonding of atoms of the same element into chains or rings)
The unique property of a chemical element to be able to form continuous links with other same atoms through covalent bond to form straight or branched chains of varying lengths or rings of different sizes, are called catenation. This property is prominent among carbon atoms, significant among sulphur and silicon atoms and slightly present among germanium, nitrogen, selenium and tellurium atoms. The ability of greater extent of catenation of carbon atoms over silicon atoms is mainly based on the strength of carbon-carbon bonds which is much stronger than silicon – silicon bonds and also because of its small size.
In addition, carbon atoms may be linked by single, double or triple bonds. Carbon compounds, in which carbon atoms are linked by single bonds only, are called saturated compounds. Carbon compounds having double or triple or both bonds between their carbon atoms are known as unsaturated compounds.
(2) Tetracovalency / Tetracovalent nature of carbon (Tetra = four + valent = valency)
Carbon has four electrons in its outermost shell (K = 2 , L = 4). Therefore, it makes 4 bonds with other carbon atoms or monovalent atoms, to achieve noble gas configuration (Neon-2,8) and becomes stable. The four valencies of carbon can be shown as –
♦ Valence shell electrons – the electron present in the outermost shell of an atom. e.g. – carbon has four valence shell electrons.
(3) Tendency to form strong C-C covalent bonds, multiple bond and bonds with other elements–
Carbon forms multiple bonds(double and triple bonds) with other carbon atoms (C=C , C=C) and elements such as nitrogen, oxygen etc. due to its small size. The bonds that carbon forms with other elements are very strong which makes these compounds exceptionally stable. The reason for the formation of strong bonds by carbon is its small size that enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.
Isomerism is a phenomenon in which a given carbon compound show two or more different structures, have similar molecular formula and molecular weight but different properties. The different structures form from the compound are called isomers. Isomerism is also a reason of availability of large number of carbon compounds.
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