The melting point of is and that of is (it sublimes) because :

CHEMISTRY · Single correct · A Level · Chemistry · Bonding · Bonding

Problem

The melting point of

\text{AlF}_3

104^\circ\text{C}

and that of

\text{SiF}_4

-77^\circ\text{C}

(it sublimes) because : (1) there is a very large difference in the ionic character of the Al – F and Si – F bonds (2) in

\text{AlF}_3

\text{Al}^{3+}

interacts very strongly with the neighbouring

\text{F}^-

ions to given a three dimensional structure but in

\text{SiF}_4

no such interaction is possible (3) the silicon ion in the tetrahedral

\text{SiF}_4

molecule is not shielded effectively from the fluoride ions whereas in

\text{AlF}_3

, the

\text{Al}^{3+}

ion is shielded on all sides (4) the attractive forces between the

\text{SiF}_4

molecules are strong whereas those between the

\text{AlF}_3

molecule are weak