Classify the following species into Lewis acids and Lewis bases and show how these act as Lewis acid/base:

(a) OH– (b) F– (c) H+ (d) BCl3.

Lewis acid is defined as the substance (atom, ion or molecule) which is capable of accepting a pair of electrons.

⇒All cations are Lewis acids because they have a tendency to accept the pair of electrons. Example Ag+


⇒Molecules having a central atom with an incomplete octet. Example BF3



Lewis base is defined as the substance which is capable of donating a pair of electrons.


⇒All anions are Lewis bases because they have a tendency to donate the pair of electrons. Example F-


⇒Molecules in which one of the atoms has got at least one pair of electrons. Example NH3,



a) OH– can donate an electron pair. Hence, it is a Lewis base.


b) F– can donate an electron pair. Hence it a Lewis base.


c) H+ can accept an electron pair. Hence, it is a Lewis acid.


d) BCl3 is deficient in electron as its octet is incomplete. Hence, it can accept electron pair and is, therefore, a Lewis acid.


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