This worked example covers Comparing Ionic Compounds within Ionic Compounds for GCSE Chemistry. Revise Ionic Compounds in Bonding & Structure for GCSE Chemistry with 20 exam-style questions and 20 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 5 of 12
Practice
20 questions
Recall
20 flashcards
🧮 Comparing Ionic Compounds
The melting point of an ionic compound depends on the strength of the electrostatic attractions. Two factors affect this:
Higher charge = stronger attraction = higher melting point
• NaCl (1+ and 1-): melts at 801°C
• MgO (2+ and 2-): melts at 2852°C
• MgO has higher charges, so MUCH stronger attractions!
Smaller ions = closer together = stronger attraction
• Smaller ions can get closer to each other
• This makes the electrostatic force stronger
• MgO has small ions AND high charges — extremely high MP!
"Explain why MgO has a higher melting point than NaCl."
Answer:
Mg²⁺ and O²⁻ have higher charges (2+/2-) than Na⁺ and Cl⁻ (1+/1-) [1]
This creates stronger electrostatic attractions between ions [1]
More energy is needed to overcome these stronger forces [1]
Quick Check: Why does solid sodium chloride not conduct electricity, but molten sodium chloride does?
In solid NaCl, ions are held in fixed positions in the lattice and cannot move — no movement of charge is possible. When molten, the lattice structure breaks down and ions are free to move and carry electrical charge.