Why is the acid always the electron withdrawing group and the base always the electron donating group?

Question

i dont seem to understand can someone explain the anwser to me

Answer 1

These are essentially the Lewis definitions of acids and bases.  If you look a HCl as an example, and in aqueous solution this dissociates to H^+ and Cl^-.  The Lewis dot structure of H+ shows NO electrons, so it wants to gain electrons (electron acceptor).  The dot structure for Cl^- shows lone pairs of electrons (electron donor).  Put another way, the H+ ion accepts a pair of electrons from the Cl- ion to form a covalent bond.  The same for H2O, BF3, and any other acid/base pair.