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Last updated date: 26th Nov 2023
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MVSAT Dec 2023

Why does $AlC{l_3}$ not show back bonding?

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Hint: Compounds with the formula $AlC{l_3}$ are known as aluminium chloride or aluminium trichloride. They are made up of aluminium and chlorine atoms in a $1:3$ ratio, with one shape containing six hydration waters. Both are white solids, but samples frequently contain iron$(III)$ chloride, which gives them a yellow appearance.

Complete answer:
When one atom in a compound has a lone pair of electrons and the other has empty orbitals next to each other, back bonding occurs. Because pi-bonding occurs after the formation of a sigma bond, a compound with back bonding has pi-bonding characteristics.
Several chemical compounds exhibit back bonding, which is a form of resonance. Back bonding is considered to give chemical compounds more stability. It is also considered to have an effect on the molecule's overall dipole moment and hybridization.
Back bonding happens when the orbitals of small atoms are the same dimension. $Al$ and $Cl$ have larger $3p$ orbitals than other elements. As a result, back bonding does not happen in $AlC{l_3}$ . Dimerization completes the octet of $Al$ in this case. The $3p$ -orbitals of $Al$ and $Cl$ are comparatively larger in dimension, which increases the bond length and prevents back bonding from achieving the double bond character. One of the $Cl$ atom's lone pairs is donated to the $Al$ atom's empty $3p$ orbital in other $AlC{l_3}$ molecules.

$AlC{l_3}$ is a covalent compound rather than an ionic one. Since the $Al$ atom has a higher polarising force, the cl electron is readily attracted to it, resulting in electron sharing. It has a covalent bond. $A{l^{3 + }}$ is a strongly charged ion that can significantly polarise the electron clouds in $Cl$.