Atoms in the elementary state, with a charge of 0, have the same amount of electrons and protons. However, whenever we refer to an ionic species of an atom, it is now with a charge different from 0.
For example, the hydrogen atom (H) has only one positive charge (proton) and one negative charge (electron). When this H atom is presented as H+, that means it has lost 1 electron, having the final charge being just +1. Just like hydrogen, atoms such as Na (sodium) or K (potassium) also tend to lose one electron, making them more likely to react, besides following the octet rule. For these cases, the cations (positive ions) for Na is Na+ and for K is K+.
For elements such as oxygen, the tendency is to gain electrons, in order to follow the octet rule. So when the tendency is to gain electrons, the atom goes from its neutral form (charge = 0) to its negatively charged form, or anion (charge < 0).
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