Explain VSEPR theory . Applying this theory to predict the shapes of `IF_(7)`, and `SF_(6)`.

Explanation

(i) The shape of the molecules depend on the number of valence shell electron pair around the central atom.
(ii) i) There are two types of electron pairs namely, bond pairs and lone pairs.
(iii) Each pair of valence electrons around the central atom repel each other and hence they are located as far away as possible in three dimensional space to minimise the repulsion between them.
(iv) The repulsive interaction between the different types of electron pairs is in the following order:
`lp-lpgtlp-bpgtbp-bp`
lp : lone pair, bp : bond pair
(v) The lone pair of electrons are localised only on the central atom and interact with only one nucleus whereas the bond pairs are shared between two atoms and they interact with two nuclei. Because of this, the lone pairs occupy more space and have greater repulsive power than the bond pairs in a molecule.
`IF_(7)` : It is an `AB_(7)` type molecule. This molecule has 7 bond pair of electrons and no lone pair of electrons. Due to bond pair-bond pair interaction of electrons, `IF_(7)` has pentagonal bipyramidal shape.

`SF_(6)`: It is an `AB_(6)` type molecule. This molecule has 6 bond pairs of electrons and no lone pair of electrons. Due to bond pair-bond pair interaction of electrons, `SF_(6)` has octahedral shape.