American chemist Gilbert N. Lewis first introduced this helpful idea in the year 1923. He defined acids as electron pair acceptors and bases as electron pair donors. This means a chemical does not have to give up a proton to be an acid.
An atom or molecule just needs an empty space to hold two extra electrons. Chemists call this empty space an incomplete octet or an empty orbital. Many positive metal ions frequently act as powerful Lewis acids in chemical reactions.
These charged metal atoms have empty outer spaces in their electron clouds. They can easily take in electron pairs from other nearby molecules. Chemists call the molecules that give up these electron pairs by the name ligands.
The Lewis model is incredibly helpful for understanding many advanced chemistry topics. It lets us understand reactions that do not happen in standard water solutions. It also explains how large complex metal structures form in nature.
Students often incorrectly think every acid must have a hydrogen atom to give away. The Lewis model proves this common assumption is simply not true. It focuses on the movement of negative electrons instead of positive protons.
Any chemical missing a full set of outer electrons is a potential Lewis acid. This model greatly broadens our overall view of how different chemicals interact.