Gilbert N. Lewis (the "dot man") proposed that acid/base behavior be described in terms of electron pairs. In his model acids accept electron pairs and bases donate them. One way of visualizing this process is to think of molecules with lone pairs as bases and those with incomplete octets as acids.

That, of course, is only the beginning. This approach broadens acid/base behavior to a considerable extent beyond even what Brønsted and Lowry proposed. An understanding of the Lewis model is not necessary for this course and this is that last you'll hear about it.