Non-metals have a larger number of outer electrons called valence electrons. Therefore, it is easier for them to "steal" valance electrons from other elements with fewer valence electrons(usually metals)
For example, Chlorine(Cl) has 7 ve-. When forming an ion it will steal one electron from a metal. and gain a charge of -1. Because the ion is NEGATIVELY charged, it will be called an anion.
Nonmetals form anions.
Vocab:
cation: Paws-itively charged ions (get it? because its a CAT ion?)
anion: negatively charged ions
