[denverkid]

I am learning about Lewis acids and bases and "adducts." We did some exercises, so Lewis acid = something that can accept electrons and Lewis bases donate electrons. According to my textbook, PF₃ + F₂  PF₅ does NOT represent the formation of a Lewis acid-base adduct. Is it because F₂ is not a Lewis base (if not, I don't understand why it isnt)? Or is it becuz each F gets added on separately instead of as one entity?
 

Additionally, can a Lewis acid/base adduct refer to two added particles? For example if there is some reaction

A + 2B  AB₂, where A is a Lewis acid and B is a Lewis base, but it goes through two steps:
A + B AB
AB + B AB₂


Would you still call A + 2B AB₂ a Lewis acid-base adduct, or would you have to refer to each step individually?