Question

Which of the following is electron deficient?
a.) $CaC{l_2}$
b.) $B{F_3}$
c.) $A{l_2}C{l_6}$
d.) $CC{l_4}$

Answer 1

Hint: A molecule is said to be electron deficient if it has a lesser number of electrons than the electrons required for maximum stability. An electron deficient molecule tries to complete its electrons by bonding with some other atoms.

Complete step by step answer:
Electron deficiency is a term used for atoms or molecules having lesser number of electrons than the electrons required for maximum stability. For each atom in a molecule, main group atoms having less than 8 electrons (octet rule) or transition metal atoms having less than 18 electrons (18 electron rule) are described as electron-deficient. For a molecule as a whole, the ones which have an incompletely filled set of bonding molecular orbitals are considered to be electron deficient.
In the given question, we will have to investigate each option to reach an outcome.
$CaC{l_2}$
$CaC{l_2}$ is an ionic compound. It breaks into $C{a^{ + 2}}$ and $C{l^ - }$ according to the reaction:
$CaC{l_2} \to C{a^{ + 2}} + 2C{l^ - }$
Both $C{a^{ + 2}}$ and $C{l^ - }$ are ionic and have a complete octet,
So, $CaC{l_2}$is not electron deficient.

$B{F_3}$
$B{F_3}$ is electron deficient as the Boron atom has only 6 electrons around it which are involved in three bonds with the fluorine atom. Generally, compounds of group 13 are electron deficient.
So, $B{F_3}$ is electron deficient.

$A{l_2}C{l_6}$
Aluminium is a group 13 element, the compound $AlC{l_3}$ of which is electron deficient. $AlC{l_3}$ dimerises to form $A{l_2}C{l_6}$ to be electron sufficient.
So, $A{l_2}C{l_6}$ is not electron deficient.

$CC{l_4}$
$CC{l_4}$ is not electron deficient as the carbon atom has its complete octet and has 8 electrons around it.
So, $CC{l_4}$ is not electron deficient.

Hence, the correct answer is (B).

Note: Remember that $B{F_3}$ can’t dimerise to form ${B_2}{F_6}$ as the size of fluorine is large and the size of boron is small. Thus, ${B_2}{F_6}$ doesn’t exist. However, $A{{l}_{2}}C{{l}_{6}}$ exists as dimer and is covalent in nature due to dimerisation and banana bonding. It should also be noted that $A{{l}_{2}}C{{l}_{6}}$ is dimer only in vapour state.