Give reasons for the following observations :
Why `SF_(4)` undergoes hydrolysis but not `SF_(6)`?
Or `SF_(6)` is inert towards hydroysis.
`SF_(6)` is much less reactive than `SF_(4)`.
Or (i) `SF_(4)` is easily hydrolysed whereas `SF_(6)` is not easily hydrolysed.
(ii) Sulpher exhibits greater tendency for calenation than selenium.
(iii) Sulpher has a higher tendency for catenation than oxygen.

Explanation

(i) In `SF_(6)`,S is stericallly protected by six F atoms and hence does not allow `H_(2)O` molecules to attack the S atom. Furthermore, F does not have d-orbitals to accept the electrons donated bt `H_(2)O` molecules. As a since it is surrounded by only four F atoms. As a result, attack of `H_(2)O` moleucles on S atom can take place easily and hence htdroysis occurs.
(ii) As we move from S to Se, the atomic size increases and hence the strength of E-E bond decreases. As a result, S-S bond is much stronger than Se-Se bond and consequently, S shows greater tendency for catendation than selenium.
(iii) Due to Small size, the lone pairs of electrons on the O atoms repel the bond pair of the O-O bond to a greater extend that the lone pairs of electrons on the S atom in S-S bond. As a result, S-S bond is much stronger `(213 kJ mol^(-1))` than O-O bond `(138 kJ mol^(-1))` and hence S has a much stornger tendecy for catendation than O.