Question

Why is $ FeC{{l}_{3}} $ ​ a Lewis acid?

Answer 1

Hint: The inorganic compound iron(III) chloride with the formula ( $ FeC{{l}_{3}} $ ). It's also known as ferric chloride, and it's a common iron compound with a +3 oxidation state. With a melting point of $ 307.6\text{ }{}^\circ C $ , the anhydrous chemical is a crystalline solid. The colour of the crystals varies depending on the viewing angle: reflected light appears dark green, while transmitted light appears purple-red.

Complete Step By Step Answer:
A Lewis acid is a chemical species with an empty orbital that may accept an electron pair from a Lewis base and create a Lewis adduct.
Lewis acids accept a pair of electrons. Lewis acids are electrophilic, which means they attract electrons. The acid employs its lowest vacant molecular orbital when interacting with a base.
Lewis acids can come in a variety of forms. Because they can receive electrons, all cations are Lewis acids. $ C{{u}^{2}}^{+},\text{ }F{{e}^{2}}^{+},\text{ }F{{e}^{3}}^{+} $ , etc.)
An incomplete octet of electrons in an atom, ion, or molecule can behave as a Lewis acid (e.g., $ B{{F}_{3}},\text{ }Al{{F}_{3}} $ ).
Lewis acids are molecules in which the core atom has more than 8 valence shell electrons and so can act as electron acceptors (e.g., $ SiB{{r}_{4}},\text{ }Si{{F}_{4}} $ ).
Molecules with numerous bonds between atoms with various electronegativities (e.g., $ C{{O}_{2}},\text{ }S{{O}_{2}} $ )
Fe is in Period 4 of the Periodic Table.
Its electron configuration is $ [\mathrm{Ar}] 4 \mathrm{~s}^{2} 3 \mathrm{~d}^{6} $ . It has eight valence electrons.
In order to obtain a [Kr] configuration, it can add up to ten more electrons.
In $ \mathrm{FeCl}_{3} $ , the three $ \mathrm{Cl} $ atoms contribute three more valence electrons to make a total of 11 .
The Fe atom can easily accept more electrons from an electron-pair donor.
For example,
 $ \mathrm{Cl}^{-}+\mathrm{FeCl}_{3} \rightarrow \mathrm{FeCl}_{4}^{-} $
Since $ \mathrm{FeCl}_{3} $ can accept electrons, $ \mathrm{FeCl}_{3} $ is a Lewis acid.

Note:
Acids and bases are crucial components of chemistry. The Lewis acid/base motif, which expands the concept of an acid and base beyond H+ and OH- ions as defined by Bronsted-Lowry acids and bases, is one of the most relevant theories. Throughout the history of acid and base chemistry, the Bronsted acid-base hypothesis has been employed. However, this theory is rather limited, as it only considers acids and bases as proton donors and acceptors. In other cases, like in solids and gases, the theory does not always suit the situation.