Cu2+ (aq) reacts with ammonia to form the complex ion [Cu(NH)3)4]2+. Explain this reaction in terms of acid-base theory, and outline the bonding in the complex formed between Cu2+ and NH3

Ammonia acts as the Lewis base in this reaction by donating its lone pair of electrons, whilst Cu2+ (which is an electron deficient, electrophile) accepts the lone pair of electrons from the ammonia, making it a Lewis acid. The bond between Cu2+ and NH3 is a coordinate bond (also known as a dative bond), whereby the electrons in the bond are both donated by one species (in this case NH3). Thus NH3 is a ligand. Cu2+ is the electrophile (electron deficient) and NH3 is the nucleophile (electron rich).