Structure and bonding · GCSE Chemistry
Ionic bonding
GCSE Chemistry revision on ionic bonding: electron transfer from metal to non-metal, giant ionic lattices, and why salts have high melting points but only conduct when molten or dissolved.
Transfer, not share. Metals lose, non-metals gain, then opposite charges attract in a giant lattice. Solid ionic compounds do not conduct; molten or aqueous ones do, because the ions can move.
The important bits
What you need to know
- 1
Ionic bonding is the strong electrostatic attraction between oppositely charged ions, formed when electrons transfer from a metal atom to a non-metal atom.
- 2
Sodium (2,8,1) transfers one electron to chlorine (2,8,7): Na → Na⁺ + e⁻ and Cl + e⁻ → Cl⁻. Both ions have noble-gas structures (2,8 and 2,8,8).
- 3
Magnesium and oxygen: Mg (2,8,2) loses two electrons to form Mg²⁺; O (2,6) gains two to form O²⁻. The compound is MgO, a giant ionic lattice.
- 4
The structure is a giant ionic lattice: each positive ion is surrounded by negative ions and vice versa. The electrostatic forces act in all directions.
- 5
Ionic compounds have high melting and boiling points because a lot of energy is needed to overcome those strong attractions. MgO melts higher than NaCl because 2+ and 2− attract more strongly than 1+ and 1−.
- 6
They conduct electricity when molten or dissolved in water, because ions are free to move and carry charge. They do not conduct as solids: the ions are locked in place.
- 7
Many ionic compounds dissolve in water. Water molecules attract the ions and pull them out of the lattice. Not all ionic compounds are soluble: CaCO₃ is a common exception.
- 8
Compared with simple covalent molecules, ionic compounds have much higher melting points, conduct when molten or aqueous, and are usually solids at room temperature. They shatter when hit because like charges align as the layers shift.
Quotations worth analysing
Short evidence. Real method.
“Ionic bonding is the electrostatic attraction between oppositely charged ions.”
Name the force, not just “they transfer electrons”. Transfer explains how the ions form; attraction is the bond that holds the lattice together.
“2Na(s) + Cl₂(g) → 2NaCl(s)”
Metal plus non-metal is the classic ionic story. The product is a giant lattice of Na⁺ and Cl⁻, not a molecule of NaCl. State symbols show a solid salt from a metal and a gas.
“Mg → Mg²⁺ + 2e⁻ O + 2e⁻ → O²⁻”
Electrons lost by the metal equal electrons gained by the non-metal. The charges then cancel in MgO. This is not a covalent shared pair.
Go deeper
Bonding names the force; lattice names the structure
Students write “ionic” when the mark scheme wanted “giant ionic lattice”. Bonding is the electrostatic attraction. Structure is the repeating 3D pattern of ions. High melting point is a lattice story: strong forces in all directions. Conductivity is a mobile-ion story: solid NaCl has ions but they cannot move, so it is an insulator; molten NaCl and NaCl(aq) conduct. Metals conduct for a different reason — delocalised electrons — so do not say salt conducts because it has free electrons. That comparison is a favourite six-mark: ionic versus metallic conduction, or ionic versus simple molecular melting points.
Go deeper
Contrast ionic properties with simple covalent ones
Sodium chloride melts at 801 °C and conducts when molten. Water, a simple covalent molecule, melts at 0 °C and does not conduct (pure water is a very poor conductor). The covalent bonds inside H₂O are strong, but the forces between molecules are weak, so little energy is needed to separate them. In NaCl there are no molecules to separate: you must break ionic bonds throughout the lattice. Ionic compounds are usually soluble in water and insoluble in organic solvents; many simple molecules do the reverse. When a question says “explain the difference in melting point”, name both structures and the force that must be overcome in each. “Ionic is stronger” is not enough.
Go deeper
Charge and size change the melting point
MgO has Mg²⁺ and O²⁻ packed in a lattice. The 2+/2− attraction is stronger than Na⁺/Cl⁻, so magnesium oxide has a much higher melting point. That is why it is used in furnace linings. Do not invent a covalent bond in MgO because it is “an oxide”. Metal oxides of Groups 1 and 2 are ionic. If a crystal is hit, layers of ions shift so that like charges sit next to each other and the lattice splits — that is why ionic crystals are brittle, unlike malleable metals. Link the property to the particle picture every time.
See the idea in action
Explain why sodium chloride has a high melting point but does not conduct as a solid, while molten sodium chloride does conduct. NaCl is a giant ionic lattice of Na⁺ and Cl⁻. Strong electrostatic attractions act in all directions, so a lot of energy is needed to melt it. In the solid the ions cannot move, so charge cannot flow. When the lattice melts, ions are free to move to the electrodes and the liquid conducts. This is the opposite of a metal, which conducts while solid because delocalised electrons move.
Exam technique
Turn knowledge into marks
Always name giant ionic lattice, electrostatic attraction, and whether ions can move. Contrast with simple molecules (weak intermolecular forces, do not conduct) when the question compares properties.
Common mistakes
Do not give these marks away
- 01
Saying ionic compounds conduct as solids, or that they conduct because of delocalised electrons.
- 02
Calling NaCl a molecule, or saying ionic bonds are weak because salt dissolves.
- 03
Forgetting that melting point depends on ionic charge as well as on “being ionic”.
Why does solid sodium chloride not conduct electricity?
AIt has no charged particles
BThe ions are not free to move in the giant lattice
CIt is a simple molecule with no electrons
DSodium chloride is covalent in the solid state
Show the answer
The ions are not free to move in the giant lattice. Ionic compounds contain ions, but in the solid the ions are locked in place. They can carry charge only when the lattice is molten or the salt is dissolved.
Quick questions
If this is the bit you searched
What is ionic bonding GCSE Chemistry?
The electrostatic attraction between oppositely charged ions, formed when a metal transfers electrons to a non-metal. The structure is a giant ionic lattice.
Why do ionic compounds have high melting points?
Strong electrostatic forces between oppositely charged ions act in all directions in the giant lattice. A lot of energy is needed to overcome them.
When do ionic compounds conduct electricity?
When molten or dissolved in water, because the ions are free to move and carry charge. Solid ionic compounds do not conduct.
How is ionic bonding different from covalent bonding?
Ionic bonding is electron transfer and attraction between ions in a giant lattice. Covalent bonding is sharing of electron pairs between non-metal atoms. Their properties (melting point, conductivity) follow from that difference.