Give reasons:

A. Red phosphorus is less reactive than white phosphorous

B. Sulphur shows greater tendency for catenation than oxygen.

C. ClF₃ is known but FCl₃ is not known.

A)

Red phosphorous has intermolecular chain structure which increases the stability, whereas white phosphorous has tetrahedral geometry with strained bond angels due to large atomic size of phosphorous atom. Thus white phosphorous reacts more readily as compared to red phosphorous

B)

Oxygen has smaller atomic radii and thus the electronic repulsion is large due to the two lone pairs over atoms of oxygen. Also the nuclear repulsion increases due to close proximity. This decreases its tendency to catenate. Sulphur has large atomic radii as compared to oxygen and also the electrons are further apart which decreases the repulsion of electrons. The natural occurrence of sulphur is in S8 form and on heating or in hot environment the atomic bond breaks and interlinked long chained structure of sulphur can be obtained. Thus, Sulphur shows greater tendency to undergo catenation than oxygen.

C)

Interhalogen compounds are formed when there are empty orbitals present in the central atom. Fluorine has Z = 9 and electronic configuration of 1s² 2s² 2p⁵ and requires only one electron to achieve noble gas configuration. Also the higher energy orbitals are not available as they require high energy to activate and also it does not contain any d-orbital to expand its octet. So it cannot form inter halogen compounds.

For the case of chlorine the atomic number Z = 17 and outer electronic configuration as 3s² 3p⁵ 3d⁰. As there is empty d-orbital, the outer shell configuration can be expanded to form inter halogen compounds and the incoming electrons from fluorine atoms can be placed in the higher energy d-orbital. Thus chlorine accepts three fluorine atoms to form ClF₃ compound.