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Ionic compounds conduct electricity when melted or dissolved because the ions are free to move, but not when solid. Free GCSE Chemistry notes and 10 FAQs.
Electrical Conductivity of Ionic Compounds is part of How bonding and structure are related to the properties of substances in GCSE Edexcel Higher Chemistry.
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Ionic compounds conduct electricity when melted or dissolved because the ions are free to move, but not when solid. Free GCSE Chemistry notes and 10 FAQs.
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Use this lesson to stay inside How bonding and structure are related to the properties of substances while connecting the detail back to the wider Topic 1: Key concepts in chemistry topic.
Read the core explanations from Electrical Conductivity of Ionic Compounds before testing yourself from memory.
Most materials around you are electrical insulators. Wood, plastic, glass - they all block the flow of electricity. But what about ionic compounds like salt?
Picture a crystal of sodium chloride (table salt). The sodium and chloride ions are locked in a rigid 3D structure called an ionic lattice. Each ion is surrounded by oppositely charged neighbours, held firmly in place by strong electrostatic forces.
For electricity to flow, we need charged particles that can move. In solid ionic compounds, the ions are trapped in their lattice positions. They can't move, so they can't carry electrical charge from one place to another.
Everything changes when you heat an ionic compound until it melts, or when you dissolve it in water. The rigid lattice structure breaks down, and suddenly the ions are free to move around.
When sodium chloride melts at 801°C, the strong electrostatic forces holding the lattice together are overcome by thermal energy. The ions break free from their fixed positions and can move independently through the molten liquid.
The same thing happens when you dissolve salt in water. Water molecules surround each ion, weakening the electrostatic attractions between them. The ions separate and become mobile in the solution.
Now we have the key ingredient for electrical conductivity: mobile charged particles. When you connect electrodes to molten salt or salt solution, something fascinating happens.
The positive sodium ions (Na⁺) are attracted to the negative electrode (cathode). The negative chloride ions (Cl⁻) move towards the positive electrode (anode). This movement of charged particles is an electrical current.
Worked example: How Electrical Conduction Works in Ionic Solutions
Explain the process when electrodes are placed in sodium chloride solution
Answer: Mobile ions in solution act as charge carriers, allowing electrical current to flow between electrodes
The electrical conductivity of ionic compounds depends entirely on whether the ions can move. Let's compare the three states systematically.
Solid ionic compounds: Ions locked in lattice positions. No movement possible. No electrical conductivity.
Molten ionic compounds: Lattice broken by heat. Ions free to move. Good electrical conductivity.
Ionic solutions: Lattice broken by water molecules. Ions mobile in solution. Good electrical conductivity.
This topic appears frequently in GCSE exams, often worth 4-6 marks. The key is explaining the link between ion mobility and electrical conductivity clearly.
Mark-winning phrase: 'When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.' This covers all the key points examiners are looking for.
Exam precision note: In Electrical Conductivity of Ionic Compounds - Properties of ionic compounds - How bonding and structure are related to the properties of substances, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
The presence of ions is not enough on its own to explain conductivity. In a solid ionic lattice the ions are locked in place, so charge cannot flow through the structure. Once the lattice is molten or dissolved, the ions are mobile and can carry charge from one electrode to the other.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Solid ionic compounds do not conduct electricity because their ions are locked in lattice positions. Molten ionic compounds and ionic solutions conduct well, because the lattice is broken down by heat or water and the ions are free to move.
When melted or dissolved in water, ionic compounds conduct electricity because the lattice breaks down and the ions are free to move, so charge can flow. Mobile ions carry charge from one electrode to the other.
Mobile ions are ions that are free to move and carry electrical charge. They are found in molten ionic compounds and ionic solutions, where the lattice structure has been broken down.
Solid ionic compounds do not conduct electricity because the ions are locked in fixed positions in the ionic lattice by strong electrostatic forces. The ions cannot move, so they cannot carry electrical charge from one place to another.
In sodium chloride solution, Na⁺ ions move towards the negative electrode (cathode) and Cl⁻ ions move towards the positive electrode (anode). This movement of charged particles is an electrical current, while electrons flow through the external wire to complete the circuit.
When salt dissolves in water, water molecules surround each ion, weakening the electrostatic attractions between them. The ions separate from the lattice and become mobile in the solution, so the solution can conduct electricity.
Molten salt conducts electricity because when sodium chloride melts at 801°C, the ions break free from their fixed positions. The mobile ions can then move through the liquid and carry charge.
Molten lead bromide is an electrolyte, a substance that conducts electricity when molten or dissolved in water because of the presence of mobile ions. Sodium chloride solution is another example.
The presence of ions is not enough on its own to conduct electricity. In a solid ionic lattice the ions are locked in place, so charge cannot flow; only when molten or dissolved are the ions mobile.
Moving ions carry the current in an ionic solution: Na⁺ ions move towards the cathode and Cl⁻ ions move towards the anode. Electrons flow through the external wire, and both parts are needed to complete the circuit.