The amount of carbon present in the earth’s atmosphere and its crust is quite low. There is only 0.02% carbon in the earth’s crust existing in the form of minerals (such as carbonates, coal, hydrogen carbonates) and 0.03% carbon in the earth’s atmosphere existing in the form of carbon dioxide.
In spite of this small amount of carbon available in nature, carbon holds an utmost importance in chemistry. It’s so important that whole of chemistry is divided into two parts – organic chemistry (chemistry of compounds containing carbon) and inorganic chemistry (chemistry of compounds which doesn’t contain carbon). It’s very surprising but as evident from the name itself, organic chemistry is also chemistry of organic (or living) things and all living or organic things have carbon in them.
Carbon, just like the other first members of their respective groups, is peculiar from the other members of the group. This behaviour is observed in carbon mainly due to it’s:
- Small size of the atom
- High electronegative
- High ionization enthalpy
- Unavailability of d-orbital’s
The reasons behind this anomalous behaviour of carbon are as follows:
Tetravalency of Carbon
Carbon has tetravalency i.e. it can share four electrons to complete its octet and so it can be bonded to four different monovalent atoms. Carbon from a large variety of compounds with oxygen, nitrogen, hydrogen, halogens resulting in a different set of compounds which have distinctive characteristics and properties.
Due to the availability of only s and p orbitals, it can hold only four pairs of electrons in its valence shell. Thus, the covalence can be limited to four but other elements of the group have greater covalence due to the existence of d-orbital.
Carbon has a unique feature of forming long carbon chains i.e. it attaches with other carbon atoms to form long carbon chains. This property is known as catenation. This chain can be as big as to contain a total of 70-80 carbon. This gives rise to very complex compounds having straight carbon chain, branched carbon chain and ring. The carbon compounds having only single bond are known as saturated hydrocarbons whereas compounds having double or triple bond are known as unsaturated hydrocarbons.
Small size of carbon
Most of the properties of carbon are also because of its small size. Compounds formed by carbon are highly stable, because of its small size. Due to its small size, the nucleus can effectively hold on to bonded and nonbonded electrons.
Hence, in short tetravalency, small size and property of catenation make carbon different from other elements and so we have the whole branch of chemistry dedicated to the study of this kind of compound.