A chemistry teacher once tried to teach me what a molecule is, but it didn t stick, thanks to my chronically slippery brain which refuses to retain useful information. Please correct me in the comments below, but as far as I understand the situation, molecules are like atoms but larger and with some fun accessories. If atoms are footballs, let s say, then molecules are those big nets filled with footballs you see hanging outside shops in seaside towns. Some molecules are good and clump together to form chemicals we like, such as water and sunshine. Other molecules are horrible and conspire to form the things we hate, like bad dreams and dangerous knock-out gases.