Question

The compound that is not a Lewis acid is:
(A) $ BaC{l_2} $
(B) $ AlC{l_3} $
(C) $ BC{l_3} $
(D) $ SnC{l_4} $

Answer 1

Hint: Lewis base and Lewis acid are more or less equivalent with the words nucleophile and electrophile. However, these words highlight the kinetic component of reactivity, particularly their abstract noun forms nucleophilicity and electrophilicity, whereas Lewis basicity and Lewis acidity emphasise the thermodynamic aspect of Lewis adduct production.

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. Because it may receive a lone pair, trimethylborane is a Lewis acid. The Lewis acid and base share an electron pair provided by the Lewis base in a Lewis adduct, producing a dative bond. In many situations, the interaction between the Lewis base and Lewis acid in a complex is represented by an arrow representing the Lewis base contributing electrons to the Lewis acid.
 $ M{e_3}B{\text{ }} + {\text{ }}:N{H_3}\; \to \;{\mathbf{M}}{{\mathbf{e}}_{\mathbf{3}}}{\mathbf{B}}:{\mathbf{N}}{{\mathbf{H}}_{\mathbf{3}}} $
Barium chloride, $ BaC{l_2} $ , is not a Lewis acid because barium loses two electrons while chlorine gets one, resulting in the chloride ion. It is not a Lewis acid since both species contain full octets. Because it is an ionic compound with both ions having a full octet, it does not behave as a lewis acid. This is because, in order to produce chloride ions, Barium loses two electrons (dropping two valence electrons and therefore achieving noble gas configuration) while the chlorine atoms gain one electron each (now containing 8 electrons in its valence shell). As a result, both species have full octets.
All other compounds have incomplete octet hence may react as lewis acids.
Hence option A is correct.

Note:
Although there have been attempts to distinguish dative bonding from non-dative covalent bonds using computational and experimental energetic criteria, for the most part, the distinction merely notes the source of the electron pair, and dative bonds, once formed, behave similarly to other covalent bonds, though they typically have significant polar character.