On the basis of VSEPR theory, predict the shapes of given molecules: PCl₅ and SF_6.

(i) PCl₅ molecule. The electronic configuration of central phosphorus atom is

It has five valence electrons. All the five electrons are mutually shared with the electrons of five chlorine atoms to form five P - Cl bonds as shown.

Hence, P atom is surrounded by five shared pairs of electrons. These repel each other and take up such positions and there is no further repulsion between them. The most favourable arrangement is trigonal bipyramidal.

(ii)  SF₆ molecule: The electronic configuration of central sulphur atom is

It has six valence electrons. 
All the six valence electrons are mutually shared by the electrons of six fluorine atoms to form six S – F bonds.

Hence, S atom is surrounded by six shared pairs of electrons (six bond pairs). These repel each other and try to remain as far apart as possible so that there is no further repulsion between them. Under such conditions, the most favourable arrangement is octahedral.