Chapter 4 Solutions — Carbon and its Compounds

Carbon has 4 valence electrons and each oxygen has 6 valence electrons.

Carbon needs to share 4 electrons (2 with each oxygen) to complete its octet.

Each oxygen shares 2 electrons with carbon, forming a double bond on each side.

Electron dot structure:

O::C::O

(Each '::' represents a double bond = 2 shared pairs of electrons)

Each oxygen also has 2 lone pairs of electrons.

All three atoms achieve a stable octet configuration.

(i) Catenation: Carbon has the unique ability to form bonds with other carbon atoms, giving rise to large molecules. This is because of the strong C-C bond (bond energy 346 kJ/mol). Carbon can form single, double, and triple bonds with itself.

(ii) Tetravalency: Carbon has a valency of 4, so it can bond with four other atoms of carbon or atoms of other elements. It forms strong covalent bonds with hydrogen, oxygen, nitrogen, sulphur, chlorine, and many other elements.

These two properties together result in the formation of a huge number of carbon compounds with different structures and properties.

Diamond:

Each carbon atom is bonded to 4 other carbon atoms forming a rigid three-dimensional tetrahedral structure.

All bonds are strong single C-C covalent bonds.

This makes diamond the hardest known natural substance.

Diamond has a very high melting point and does not conduct electricity (no free electrons).

Graphite:

Each carbon atom is bonded to 3 other carbon atoms in the same plane, forming hexagonal layers.

The fourth electron of each carbon is free to move, making graphite a conductor of electricity.

The layers are held together by weak van der Waals forces, so they can slide over each other.

This makes graphite soft and a good lubricant.

Both are allotropes of carbon — same element, different physical properties due to different bonding arrangements.