Question

How can I tell which substances are donating electrons and which are accepting electrons?

Identify the Lewis acid and Lewis base that lead to the formation of the following species: (a) AICI, (b) Cd(CN) (c) HCO3, (d) H SO

Answer 1

Lewis acid:

Substance that can accept pair of electrons must have vacant orbital so that it accept pair of electrons.

like H⁺ , there is no electron it has vacant 1s orbital so it can accept two electrons to attain Helium like electronic configuration. Hence H⁺ is lewis acid.

in AlCl₃ charge of Al = +3,

Al³⁺ has vacant 3s orbital so it can accept pair of electrons. hence AlCl₃ is lewis acid.

Cd²⁺ also has vacant 5s orbital. so Cd²⁺ is lewis acid.

Lewis base:

The Lewis base has two nonbonding electrons so they can donate pair of electrons.

They have filled orbitals containing an electron pair that is not involved in bonding.

like in Cl^- all the orbitals are completely filled and two electrons are not involved in bonding .

in CO₃^2- , oxygen atoms are completely filled and two of them has nonbonding electron pair.

CN^- and HSO₄^- both have nonbonding electrons so they are lewis bases.

o=c- + H+ donor 0 : a acceptor oze O-H