Medical College Admission Test (MCAT) General Chemistry Practice Exam

A Lewis base is defined as a substance that donates an electron pair to form a covalent bond. This definition is fundamental in the context of Lewis theories of acid-base chemistry, where a Lewis acid is defined as an electron pair acceptor and a Lewis base is an electron pair donor.

In this case, the answer indicating that a Lewis base accepts electrons is correct, but it’s important to clarify the language. While Lewis bases are indeed electron pair donors, they can also interact with species that are electron deficient, functioning in reactions where they contribute an electron pair to form new bonds.

This concept is distinct from other types of acids and bases, such as Brønsted-Lowry acids and bases, where acids are proton donors and bases are proton acceptors. This distinction helps in recognizing that Lewis acid-base interactions can occur without the involvement of protons.

The other options relate to different definitions within acid-base chemistry. Certain choices identify behaviors associated with Brønsted-Lowry acids and bases or offer context that does not pertain directly to the Lewis definition, distinguishing the clarity needed when discussing Lewis bases specifically.