In informal situations, if and whether function more or less as equals, though they are not equals in careful writing. If is a conditional and whether introduces an alternative. Tell me if you’ll come means you should only respond if you are coming. Tell me whether you’ll come asks for a response no matter your decision. Be aware that the conditional if can be better hidden than in the previous example: He asked if he can go home means he asked only when he was able to go home, while He asked whether he can go home means he asked a yes or no question concerning his ability to go home.