Question

The melting point of $Al{F}_3$ is ${1291}^{\circ }C$ and that of $Si{F}_4$ is - ${77}^{\circ }C$ (it sublimes) because :

• A. there is a very large difference in the ionic character of the Al-F and Si-F bonds
• B. in $Al{F}_3,$ $A{l}^{3+}$ interaction is possible
• C. the silicon ion in the tetrahedral $Si{F}_4$ is not shielded effectively from the fluoride ions whereas in $Al{F}_3,$ the $A{l}^{3+}$ ion is shielded on all sides
• D. the attractive forces between the $Si{F}_4$ molecules are strong whereas those between the $Al{F}_3,$ molecules are weak

Answer 1

The correct option is B in $Al{F}_3,$ $A{l}^{3+}$ interaction is possible

$Al{F}_3$ is ionic in nature while $Si{F}_4$ is covalent in nature. So, $Al{F}_3$ has high melting point than $Si{F}_4$