Question

State the reason why carbon can neither form ${C^{4 + }}$ cations nor ${C^{4 - }}$ anions but forms covalent compounds. Also, state reasons to explain why covalent compounds:
(i) are bad conductors of electricity.
(ii) have low boiling and melting points.

Answer 1

Hint: Carbon is a chemical element of the periodic table having an atomic number six and the electronic configuration is such that it can either gain four electrons or lose four electrons to complete its octet. In order to complete its octet, it undergoes mutual sharing of electrons to form covalent bonds with other elements rather forming bonds by transfer of free electrons.

Complete step by step answer:
The atomic number of Carbon is 6. The electronic configuration of carbon is \[1{s^2}2{s^2}2{p^2}\] . In much more simpler terms, the electronic configuration of carbon can also be written as $2,4$. Hence, carbon has 4 electrons in its valence shell. It has to either lose or gain 4 electrons in order to gain a stable electronic configuration. It cannot gain four electrons as a carbon atom has a total of 6 protons and is very small to handle ten electrons. It cannot even donate the electrons as it needs a lot of ionization energy to do so. Hence, it cannot form \[{C^{4 + }}\] cation or \[{C^{4 - }}\] anion and thus forms a covalent bond by mutual transfer of electrons.
(i) Covalent compounds formation takes place by the mutual sharing of electrons. The Carbon atom doesn’t have a free electron which is required for the transfer of electricity as electricity is the flow of free electrons and thus, they are poor conductors.
(ii) Covalent compounds have low melting and boiling points because they have weak intermolecular forces between bonds. Hence, less amount of energy or less temperature is required to break the bonds.


Note:
Due to its tendency to form a large number of covalent bonds, the carbon atom can easily form huge ring, cage or chain like structures. For instance, the graphite and diamond structure are stronger than the cage and ring structures formed by the elements of the same group as that of carbon because of its low size and tendency to accommodate easily in the interstitial sites in the covalent compound.