Question

GIVE REASONS FOR THE FOLLOWING: [SiF6] 2- is known but [SiCl6] 2- is not known. Diamond is covalent yet it has high melting point Boric acid is considered as a weak acid Boron is unable to form BF6 3- ion BF3 behaves like a Lewis acid

Answer 1

The main reasons are;
due to smaller size of F as compared  to Cl , six small F atoms can be easily accommodated  around si atom while cl cannot since f are present in smaller 2p orbital and cl are present in larger 3p orbital therefore interaction of f lone pair  electron with d orbitals of silicon are stronger in f as compared cl

diamond has three dimensional network structure involving strong c-c bond .these bonds are difficult to break and           hence melting point of diamond is very high 

because it does not release H+ions on its own it accepts OH- ion from the water molecule to complete its octet and in turn releasee H+ ion therefore it is a weak acid 

due to absence of d qrbitals b at the maximum can accommodate 8 electrons or 4 pairs of electron but not BF36 Iin which the covalency of b is  6

Answer 2

Here's your answer .

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