Ions: Formation and Charges

An ion is an atom (or molecule) with a net electrical charge due to gain or loss of electrons.
Atoms are neutral when the number of protons equals the number of electrons; otherwise they carry a charge.
Ions form by electron transfer: losing electrons creates a positive charge; gaining electrons creates a negative charge.

Cation: positively charged ion; formed when an atom loses one or more electrons.
Anion: negatively charged ion; formed when an atom gains one or more electrons.
Charge notation: positive charges as $+1$, $+2$, etc.; negative charges as $-1$, $-2$, etc. For clarity: $+1$ , $-2$ .
Charge calculation can be summarized as $Q = Z - N<em>e$ , where $Z$ is the atomic number (protons) and $N</em>e$ is the number of electrons.
- Example: Sodium (Z = 11) loses one electron → $Q = 11 - 10 = +1$ , so the ion is $+1$ .
- Example: Oxygen (Z = 8) gains two electrons → $Q = 8 - 10 = -2$ , so the ion is $-2$ .

Metals (left side of the periodic table) tend to lose electrons and form cations.
Nonmetals (right side) tend to gain electrons and form anions.