CARBON:IT'S UNIQUENESS AND BONDING.

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(Edited)

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People do things different in a way that no other person will do it or even has a special characteristics in them, this is called their uniqueness. So also does carbon has its own uniqueness among other elements in the periodic table. These unique features make it exceptionally different from others.

UNIQUENESS OF CARBON

Of all the elements of the periodic table, carbon is most unique. This is established by the fact that today, there exist several million compounds of carbon whereas there are only several thousand compounds of all the other elements on the periodic table put together. The unequalled tendency for catenation. (chain forming) coupled with existence of different possible structural and spatial arrangements of carbon skeletons are some of the peculiar features of the carbon atom. Catenation is the ability of carbon to form a long chain. Branching and different arrangements result in different compounds entirely, this phenomenon is called isomerism.
Typical organic compounds are liquids or low melting solids as distinct from inorganic compounds most of which are high melting solids. The chemical reactions of organic compounds are in most cases very slow while inorganic reactions often proceed instantaneously and go to completion within a very short time.

THE CARBON ATOM

Carbon occupies position six on the periodic table, indicating that it possesses six electrons. The electrons are distributed into the K shell, which can take a maximum of two electrons, and the L shell which houses the remaining four electrons. These six electrons are arranged into orbitals, '1s' orbital of the K shell, '2s' and '2p' orbitals of the L shell such that the rules concerning the arrangements are complied with. Pauli exclusion principle, states that an orbital may contain not more than two electrons which must be of opposite spins. The second, Hind's rule, stipulates orbitals of lower energy are first filled and that degenerate orbitals are filled gradually with electrons of parallel spins and no pairing of electrons occur until all vacant orbitals have each received an electron.
In compliance with these two rules, the arrangement of the electrons of carbon at the ground state will be.

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Ground state of carbon

The 2px, 2py and 2pz orbitals being degenerate have the two electrons of parallel spin distributed into two of the three p orbitals.

CARBON IN BONDING.

When reactions take place in organic chemistry, it is because bonds have been made and bonds have been broken. The bonds which play the major roles in reactions are covalent bonds which were made by sharing of electrons between atoms. At the ground state, carbon has only two unpaired electrons and so will be expected to exhibit a valence of two(bivalency). In reality carbon is tetravalent, forming four bonds of the same length and strength when bonded to four atoms of the same element, such as in methane CH4 or carbon tetrachloride CCl4. The four electrons participating in the bonding must be of equivalent energy.
From our knowledge of ground state arrangement, the only two unpaired electrons are in the 2p orbital. The other two electrons of opposite spin are in the 2s orbital, and will not be expected to form bonds of equivalent energy and length with the 2p electrons. This puzzle has however been rationalized by invoking the concept of 'hybridization'. By this concept, it is postulated that there occurs promotion of a 2selectron to a 2p orbital such that all four electrons are of parallel spin. There occur a 'mixing' of the 2s and 2p orbitals that they assume a specific geometric distribution which makes the orbitals degenerate. The four electrons in the L shell are now arranged into the orbitals 2s, 2px, 2py, 2pz all of parallel spin. This arrangement occurs at the excited state.
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Excited state of carbon

CONCLUSION
So far so good, we've been able to treat the uniqueness of carbon as it involves catenation among others. It has also been established that carbon is tetravalent in nature i.e it must have four bonds connected to it, lesser or higher number won't be accommodated. The ground state of carbon and its excited state is not left aside as well.

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Reference

Uniqueness of carbon

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