Electrophile: A molecule or ion that accepts a pair of electrons to form a new covalent bond (same as Lewis acid).
Leaving group: A molecule or ion that leaves with a pair of electrons that used to be shared in a covalent bond with this fragment.
Lewis acid: A molecule or ion that accepts a pair of electrons to form a new covalent bond (same as electrophile).
Lewis base: A molecule or ion that shares a pair of electrons to form a new covalent bond (same as nucleophile).
Nucleophile: A molecule or ion that shares a pair of electrons to form a new covalent bond (same as Lewis base).