An acid is an electron-pair acceptor and a base is an electron-pair donor in the model.

The statement you provided is referring to the Lewis theory of acids and bases. According to this theory:

1. An acid is a substance that can accept a pair of electrons. This is because it has a vacant orbital that can accommodate a pair of electrons. This makes it an electron-pair acceptor.

2. On the other hand, a base is a substance that can donate a pair of electrons. This is because it has a lone pair of electrons that it can donate. This makes it an electron-pair donor.

So, in the Lewis model, the focus is on the transfer of electron pairs, rather than protons (as in the Bronsted-Lowry model). This allows for a broader definition of acids and bases, and includes reactions that do not involve protons.