- Giant ionic lattice = regular 3D arrangement of alternating positive and negative ions
- No molecules — the whole crystal is one continuous structure
- High melting/boiling points — many strong electrostatic forces need lots of energy to break
- Solid: no conduction — ions fixed in position, cannot move
- Molten/dissolved: conducts — ions free to move and carry charge
- Brittle — force causes layers to shift, like charges repel, structure shatters
- Higher charges = higher melting point (MgO > NaCl)
- Smaller ions = higher melting point (ions closer = stronger attraction)
Quick Check: Predict whether KCl or MgO would have the higher melting point. Give a reason.
MgO has the higher melting point. Mg²⁺ and O²⁻ have charges of 2+ and 2-, while K⁺ and Cl⁻ have charges of only 1+ and 1-. Higher charges mean stronger electrostatic attractions, requiring more energy to overcome.
This key facts covers Key Facts to Memorise within Ionic Compounds for GCSE Chemistry. Revise Ionic Compounds in Bonding & Structure for GCSE Chemistry with 21 exam-style questions and 21 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 7 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Ionic Compounds
What type of structure is found in all ionic compounds?
Explain why magnesium oxide conducts electricity when it is molten but not when it is solid.