Ionic Bonding
An ionic bond is the strong electrostatic force of attraction between oppositely charged ions, formed when electrons are transferred from a metal atom to a non-metal atom.
Key terms
- Ion: a charged particle formed when an atom loses or gains electrons.
- Metal atoms lose electrons to form positive ions (cations).
- Non-metal atoms gain electrons to form negative ions (anions).
- Ionic compounds form a giant ionic lattice, held together by strong electrostatic forces in all directions.
Sodium chloride, NaCl
- A sodium atom (2,8,1) loses one electron to form Na⁺ (2,8).
- A chlorine atom (2,8,7) gains one electron to form Cl⁻ (2,8,8).
- The oppositely charged ions attract, forming NaCl.
Worked example
Question: Explain, in terms of electron transfer, how magnesium oxide (MgO) is formed.
Answer: A magnesium atom has 2 electrons in its outer shell and transfers both to an oxygen atom, which has 6 electrons in its outer shell. This forms Mg²⁺ and O²⁻ ions, both with a full outer shell of 8 electrons. The oppositely charged ions are then held together by strong electrostatic forces of attraction.
Common mistake: saying ionic compounds are held together by sharing electrons. Sharing describes covalent bonding — ionic bonding is about electron transfer and the electrostatic attraction that follows.
