I need help distinguishing between nucleophiles and electrophiles. Like one of the examples I am given shows methanal, chloroethane, and methanamine. Now it says methanal is electrophilic because the carbonyl group is polar since the more electronegative oxygen atom has a greater share of electrons. It says chloroethane is electrophilic because of the polar character of the C-Cl bond. And finally, the methanamine is said to be nucleophilic because it has a pair of electrons to share.

Question

But methanamine is polar so how come it isn't electrophilic? And the oxygen in methanal and the Cl in chloroethane both have lone pair electrons to share, so how come they are not nucleophilic? Basically how would I distinguish between nucleophiles and electrophiles?