"Two different forms of carbon – diamond and graphite have different structures and very different physical properties even though their chemical properties are same." Explain why.

OR

State the reasons, why carbon cannot

(i) Lose four electrons to form $\mathrm{C}^{4+}$ cation, and

(ii) Gain four electrons to form $\mathrm{C}^{4-}$ anion.

How does carbon overcome this problem to form compounds?

Main Question Answer:

Diamond and graphite are two different allotropes of carbon. They have different physical properties because of the difference in the manner in which their carbon atoms are bonded to one another:

1. Structure of Diamond: In diamond, each carbon atom is covalently bonded to four other carbon atoms, forming a rigid, three-dimensional structure. This makes diamond extremely hard (the hardest substance known) and a non-conductor of electricity.
2. Structure of Graphite: In graphite, each carbon atom is bonded to three other carbon atoms in the same plane, giving a hexagonal array. One of these bonds is a double bond, satisfying carbon's valency. These hexagonal arrays are arranged in layers stacked one above the other. The weak forces between layers allow them to slide over each other, making graphite smooth and slippery. It also has free electrons, making it a very good conductor of electricity.

Chemical properties are the same because both are made up entirely of the same element, carbon. On combustion in oxygen, both produce carbon dioxide gas ($\mathrm{CO}_2$).

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OR Question Answer:

Carbon has an atomic number of $6$ with an electronic configuration of $2, 4$. To attain a stable noble gas configuration, it needs to gain or lose $4$ electrons. However, it cannot do so because:

1. Why it cannot gain four electrons (to form $\mathrm{C}^{4-}$ anion):

• It would be extremely difficult for the nucleus, which has only $6$ protons, to hold on to $10$ electrons (i.e., $4$ extra electrons) due to strong inter-electronic repulsion.

1. Why it cannot lose four electrons (to form $\mathrm{C}^{4+}$ cation):

• Removing four electrons requires a very large amount of energy. It would leave behind a highly unstable carbon cation with $6$ protons holding on to just $2$ electrons.

How carbon overcomes this problem:

Carbon overcomes this limitation by sharing its valence electrons with other carbon atoms or with atoms of other elements (like hydrogen, oxygen, nitrogen, etc.). This sharing of electrons leads to the formation of covalent bonds, allowing all participating atoms to achieve a stable noble gas configuration.