Question

How do you identify an electrophile from a nucleophile?

Answer 1

Electrons flow from nucleophile to electrophile in reactions. The former donates an electron pair, the latter is attracted to them.

Explanation:

In simple terms, nucleophiles are able to donate an electron pair to an electrophile to form a chemical bond.

So nucleophiles are species that have a pair of electrons to donate, whilst electrophiles are species that either have a positive charge or are neutral but which have empty electron orbitals which are attracted to an electron rich centre.

So something like ammonia `NH_3` is a nucleophile, as there is a "lone pair" of electrons on the nitrogen. Olefins such as ethyelene (`H_2C=CH_2` are also nucleophiles due to the ability of the double bond to split in the presence of an electrophile to donate an electron pair.

Electrophiles include such things as Lewis acids (e.g. `H_3O^+` ions) and halogens.