Why is FeCl3 a Lewis acid?

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Answer 1 · 2014-02-06T01:25:10

${FeCl}_{3}$ $"FeCl"_3$ is a Lewis acid because it can accept an electron pair from a Lewis base.

$Fe$ $"Fe"$ is in Period 4 of the Periodic Table.

Its electron configuration is ${[Ar]4s}^{2} {3d}^{6}$ $"[Ar]4s"^2"3d"^6$ . It has eight valence electrons.

In order to obtain a $[Kr]$ $"[Kr]"$ configuration, it can add up to ten more electrons.

In ${FeCl}_{3}$ $"FeCl"_3$ , the three $Cl$ $"Cl"$ atoms contribute three more valence electrons to make a total of 11.

The $Fe$ $"Fe"$ atom can easily accept more electrons from an electron-pair donor.

For example,

${Cl}^{-} + {FeCl}_{3} \to {FeCl}_{4}^{-}$ $"Cl"^"-" + "FeCl"_3 → "FeCl"_4^"-"$

Since ${FeCl}_{3}$ $"FeCl"_3$ can accept electrons, ${FeCl}_{3}$ $"FeCl"_3$ is a Lewis acid.