Explain i) Sulphur vapours, exhibits some paramagnetism ii) `ClF`, exists but `F C l_3` does not. iii)`N(CH_3)_3`, is pyramidal but `N(SiH_3)_3` is planar. iv) Interhalogen compounds are more reactive than the corresponding, elemental hálogens?

Explanation

i. Sulphur vapour consists of .S, S_4. and .S_s. molecules at higher temperatures. .S_2. molecules have unpaired electrons-similar to .O., and are thus paramagnetic
ii. CIF, can.exist because chlorine atom has vacant d orbitals in its valence shell and can extend its covalency. But F does not have any available d- orbitals. Hence F can not form.FCl, because Fican tot extend its covalency.
iit. In trimethyl amine .NCH_3_3., the .N. atom is in the .sp^3. hybridised state and is pyramidal. The .N. atom has one lone pair in .NCH_3_3.. In trisilylamine .NSiH_3_y ~N. is in the.sp hybridised state and the molecule has trigonal planar geometry. The lone pair is present in the unhybridised p- orbital. This p-orbital overlaps with empty d- orbitals on each of the three Si atoms and results in .p pi-d pi. back bonding. Since the lone pair on .N. is involved.in back bonding with vacant d orbitals of silicon. .N. has no longer a lone pair of electrons. Hence the molecule has no donor properties. It is planar. Such " .p pi-d pi. bonding is pot present in .NCH_3_1. since there are no available d orbitals in .C. atom.
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iv. Interhalogen compounds are compounds containing 2 or more halogen atoms in. their" molecules. The bond between two dissimilar halogen atoms is. weaker than the bond between tow similar halogen.atoms, ie: the bond dissociation energy is lower in interhalogen compound. Hence they are more reactive. It is due to less effective overlapping of:
atomic orbitals of two different halogen atoms than between similar atoms. .X-Y. bond is weaker than .X-X. and .Y-Y. bonds.