Question

Give reason to explain why $Cl{F}_3$ exists but $FC{l}_3$ does not exist.

Answer 1

Absence of vacant d orbital in fluorine

Electronic configuration of chlorine is
$1s^{2}2s^{2}2p^{6}3s^{2}3p^5$

In its $1^{st}$ excited state, one pair of electrons from 3p orbital is promoted to 3d orbital.



Since it has 3 unpaired electrons in its $1^{st}$ excited state, it can form 3 covalent bonds.

For example; $Cl{F}_3$



In the case of fluorine, the second shell is the outermost shell which does not have any d orbitals.

Hence, it cannot expand its covalency to form $FC{l}_3$ like Chlorine can.

Therefore, $FC{l}_3$ does not exist.