Atoms gain electrons to form anions.
Atoms lose electrons to form cations.
Back in middle school, my chemistry teacher taught me a good way to remember whether an ion was a cation or an anion. When an atom loses an electron, it becomes positive, and when an atom gains an electron, it becomes negative.
Cation sort of sounds like “cat,” which is positive (Yay! Cats!).
Anions, on the other hand, sounds like “onion,” which is negative (Ew! Onions!).
There’s other ways of memorizing it, but this way was the easiest for me.
-T.B.
