Therefore, it is Sunday. The premises could be true yet the conclusion false. Well, today could be Thanksgiving, for example. Sundays are not the only days that there is no mail delivery. Unsound, because it is invalid.
Some doctors like to play golf.
John is a doctor. Therefore, John likes to play golf. Even if the premises are true, the conclusion could be false. It is unsound, because it is invalid. All whales are mammals.