An atoms is element that doesn’t have charge because it hasn’t lost or gained any electrons. An ion is element that has a charge, indicating either + / - charge along with the number of electrons its has gained or lost.
Example:
Na+1 —> because it’s had 1 outer valence electrons that was lost to a nonmetal
O-2 —> oxygen need 2 more electrons to be stable. (8 outer valence electrons)
