Question

Which is Lewis base: \[{I_2} + {I^ - } \to {I_3}^ - \]?
A. \[{I_2}\]
B. \[{I_3}^ - \]
C. \[{I^ - }\]
D. None of these

Answer 1

Hint: In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. This theory complements the model of oxidation and reduction reactions. This theory suggests that acids react with bases to share a pair of electrons, with no charge in the oxidation numbers of atoms.

Complete step by step answer:
Lewis acid is any substance that has an empty orbital which can accept a pair of non-bonding electrons. In other words, Lewis acid is an electron pair acceptor. For example, \[BC{l_3}\], \[AlC{l_3}\] etc.
Further, a Lewis base is any substance that has a lone pair of electrons or a negative charge which can be donated to an electron-deficient species like Lewis acids. A Lewis base is therefore an electron-pair donor. For example, \[N{H_3}\], \[{H_2}O\] etc.
Now, in case of the above-given reaction,
\[{I_2} + {I^ - } \to {I_3}^ - \]
Electronic configuration of \[{I^ - }\] is
\[\left[ {Kr} \right]{\text{ }}4{d^{10}}{\text{ }}5{s^{2{\text{ }}}}5{p^6}\]
Now, the octet of valence orbital is satisfied therefore the extra electron is used to form bonds with \[{I_2}\] to form \[{I_3}^ - \].
Now, according to Lewis, a species is a base if it is electron-rich and donate lone electrons.
So, \[{I^ - }\]is a Lewis base.

So, the correct option is C.

Note:
If two Lewis bases are in the same group of the periodic table, then basicity increases as the size of the atom increases. Lewis's basic strength is proportional to the tendency to donate lone pairs of electrons. With increasing the size of anion polarizability increases, as well as the donating power and Lewis basicity.