An ion is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention, and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. The net charge of an ion is not zero because its total number of electrons is unequal to its total number of protons.
- An atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less than the number of protons in the atom.
- Positively charged ions are called cations, and negatively charged ions are called anions.
- Ions can be formed by the addition or removal of electrons from neutral atoms or molecules, by the combination of ions with other particles, or by the rupture of a covalent bond between two atoms in such a way that both of the electrons of the bond are left in association with one of the formerly bonded atoms.
