Cations

• A cation forms when an atom loses one or more electrons from its outer (valence) shell (energy level).
• Cations are positively charged because the atom has more protons (+) than electrons (–).
• Mg atom has 12 protons and 12 electrons.
• Mg+2 ion has 12 protons and 10 electrons.
• Metal elements tend to form cations.
• Example
• Mg  Mg2+ + 2 e–

Anions

• An anion forms when an atom gains one or more electrons into its outer (valence) shell (energy level).
• Anions are negatively charged because the atom has less protons (+) than electrons (–).
• F atom has 9 protons and 9 electrons.
• F– ion has 9 protons and 10 electrons.
• Nonmetal elements tend to form anions.
• Example
• F + e–  F–