Chemistry: Lewis acid, Lewis base

Tutoring chemistry, Lewis acids and bases arise. The tutor mentions them.

A Lewis acid is a species that has room, in its outer shell, for an extra pair of electrons. H⁺ is an example, but so is BH₃. H⁺, having no electrons, has room for exactly two electrons in its outer shell, whereas B in BH₃, surrounded by only six electrons, has room for two more.

A Lewis base is a species that can offer an unbonded pair of electrons (aka a lone pair). H₂O is an example, since the O in H₂O has two lone pairs. Similarly, NH₃ is a Lewis base because its N has a lone pair.

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