Consider the following :I. $\text{AlCl}_3$II. $\text{NH}_3$III. $\text{BF}_3$IV. $\text{FeCl}_3$How many of the above are Lewis acids?

Question

Prepp Team · Accepted Answer

Identifying Lewis Acids Among Given Compounds

A Lewis acid is defined as a chemical species capable of accepting an electron pair. We analyze each compound based on this definition:

I. $\text{AlCl}_3$ (Aluminum Chloride):
In $\text{AlCl}_3$, the central Aluminum atom has only 6 valence electrons, leaving it with an incomplete octet. This electron deficiency allows it to accept an electron pair, making it a Lewis acid.
II. $\text{NH}_3$ (Ammonia):
The Nitrogen atom in $\text{NH}_3$ possesses a lone pair of electrons. This lone pair can be donated to form a coordinate bond. Therefore, $\text{NH}_3$ acts as a Lewis base, not a Lewis acid.
III. $\text{BF}_3$ (Boron Trifluoride):
Similar to $\text{AlCl}_3$, the Boron atom in $\text{BF}_3$ has an incomplete octet with only 6 valence electrons. It readily accepts an electron pair, qualifying it as a Lewis acid.
IV. $\text{FeCl}_3$ (Iron(III) Chloride):
The Iron(III) ion ($\text{Fe}^{3+}$) is a metal cation with a significant positive charge. Such cations are electron-deficient and act as Lewis acids by accepting electron pairs.