Ionic Bonding

Explain how metals and non-metals form ions, and link ionic bonding to the properties of ionic compounds.

About 3 min read
  • Explain how ions form
  • Describe ionic bonding
  • Draw dot-and-cross diagrams for simple ionic compounds
  • Link structure to properties
Before you start

You can write electron arrangements such as 2,8,1. You also know that atoms with full outer shells are stable.

How ions form

Atoms can become more stable by gaining or losing electrons. Metal atoms lose outer electrons to form positive ions. Non-metal atoms gain electrons to form negative ions. A sodium atom, 2,8,1, loses one electron to form Na⁺. A chlorine atom, 2,8,7, gains that electron to form Cl⁻.

Definition: ion

An atom or group of atoms with an electrical charge.

Definition: ionic bond

The strong electrostatic attraction between oppositely charged ions.

Giant ionic lattices

Ionic compounds form a regular giant lattice. Strong forces act in all directions, so a lot of energy is needed to break them. This gives high melting points. Solid ionic compounds do not conduct electricity because their ions cannot move. When molten or dissolved, the ions can move and carry charge.

Formula of magnesium oxide

Magnesium is in Group II and oxygen is in Group VI. Find the formula of magnesium oxide.

Mg loses 2 electrons to form Mg²⁺.

O gains 2 electrons to form O²⁻.

The charges balance with one of each ion.

Answer: MgO

Electrons transfer

In ionic bonding electrons are transferred. In covalent bonding electrons are shared.

Exam focus
Say it like this“Ions can move when molten, so the compound conducts.”
Not like this“Electrons move through the molten salt.” — Ionic compounds conduct through moving ions.
Common mistakeSaying that ionic compounds conduct when solid. The ions are fixed in the lattice.

Practice

What is the charge on a Group I ion?
1+, because the atom loses one outer electron.
What ion does fluorine form?
F⁻, because it gains one electron.
Find the formula of calcium chloride.
Ca²⁺ needs two Cl⁻ ions, so the formula is CaCl₂.
Going further
Explain why sodium chloride has a high melting point but conducts only when molten or dissolved.
Its giant lattice has strong forces between oppositely charged ions, which need much energy to overcome. When solid the ions are fixed, but when molten or dissolved they can move and carry charge.

Quick check

Ionic bonding quick check

What happens to a metal atom in ionic bonding?

Removing outer electrons leaves a full shell and creates a positive ion.

What is the formula of magnesium chloride?

The 2+ metal ion needs two 1− ions so that the charges balance.

What holds an ionic lattice together?

Positive and negative charges attract strongly in every direction through the structure.
Key takeaways
  • Metals lose electrons and non-metals gain electrons.
  • Oppositely charged ions attract strongly.
  • Ionic compounds have high melting points.
  • They conduct when molten or dissolved, not when solid.
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