Ah yes, the theme song from one of the strangest movies of all time—Parent Trap. The original, that is, with Hayley Mills. I was in love with her back then. So naturally, I would choose that phrase to title a chapter on how atoms combine to form molecules. Sometimes atoms of the same kind combine, but most often it’s different kinds of atoms. There are three main ways atoms get together, and we’ll discuss all three in this chapter