Question

Suggest why compounds containing carbon chains are very common and stable, yet chains of nitrogen or oxygen atoms in compounds rarely exceed two atoms in length and the compounds are generally very reactive.

Answer 1

The property of self-linking with atoms of the same element is termed Catenation. Carbon has a unique property of linking itself to other carbon atoms to give open chain or/and cyclic structures. Catenation is favoured by atoms where atom to atom covalent bond is quite strong.

Carbon (atomic number of 6) electronic configuration is 1S² 2S¹ 2P_x¹2p_y¹2p_z¹.

Nitrogen (atomic number of 7) electronic configuration is 1S² 2S² 2P_x¹2p_y¹2p_z¹.

Oxygen (atomic number of 8) electronic configuration is 1S² 2S² 2P_x²2p_y¹2p_z¹.

Carbon has four single electrons in its outer electron orbitals and does not have any lone pair of elctrons. It can form four strong covalent bonds with other atoms including carbon atoms.

On the other hand, the nitrogen and oxygen are smaller in size (than carbon) and in addition have one and two lone pairs of electrons in its valency shell, respectively . The lone pair of electrons on the N-atoms (O-atoms) repel the bond pair of N-N bond (O-O bond). As result N-N and O-O bonds are weaker.The C-C, N-N and O-O bond strengths are 83 Kcal, 39 Kcal, and 35 Kcal, respectively. So N and O can't show catenation property due to weak bonding .

The lone pair of electrons present on oxygen and nitrogen are generally chemically reactive and hence thier compounds are generally reactive.