1.9.1States of Matter
Explaining Conductivity — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 4 parts Lesson 20 of 30 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4What Makes a Conductor
Electric current is the flow of charged particles, so a substance needs particles that are free to move.
Electric current
- Electric current The flow of charged particles;
- in metals these are electrons, while in liquids and solutions they are ions.
Mobile charge carriers
- Mobile charge carriers Electrons or ions that are free to move, and which must be present for a substance to carry a current.
Conductor
- Conductor A substance with mobile charged particles that carry a current through it when a voltage is applied.
Insulator
- Insulator A substance with no freely moving charged particles, so it cannot carry a current.
Part 2 of 4Comparing Substances
Comparing Substances
Metals
- Metals Delocalised electrons are always available, so metals conduct in the solid state and when melted.
Ionic compounds
- Ionic compounds Ions are only free to move when melted or dissolved, so solid ionic compounds are insulators.
Covalent compounds
- Covalent compounds Most covalent compounds have no ions or free electrons, so they act as insulators in every state.
| Substance type | Solid | Molten | Charge carriers |
|---|---|---|---|
| Metal | Conducts | Conducts | Delocalised electrons |
| Ionic compound | Does not conduct | Conducts | Mobile ions |
| Simple covalent compound | Does not conduct | Does not conduct | None |
Part 3 of 4Explaining the Differences
1
In a metal, the outer electrons are delocalised, so they move through the lattice when a potential difference is applied.
2
In a solid ionic compound, the ions are held in fixed positions, so no charge can flow through the solid.
3
When an ionic compound melts or dissolves, the ions separate and are free to move, carrying charge towards the electrodes.
4
Some covalent compounds, such as hydrogen chloride, react with water to form ions, which is why their solutions conduct.
5
In ionic solutions and melts it is the ions that carry the charge, not electrons moving through the liquid.
Part 4 of 4Exam Checklist & Tips
1.9.1 – Key Points for the Exam
- Conductor A substance that allows an electric current to pass through it.
- Insulator A substance that does not allow an electric current to pass through it.
- Mobile charge carrier A charged particle free to move and carry current, such as an electron or an ion.
- Electrolyte A molten or dissolved ionic compound that conducts electricity because its ions can move.
- Delocalised electron An electron in a metal that is free to move through the structure.
Common Mistakes
- Saying electrons move through an ionic solution; it is the ions that move and carry the charge.
- Claiming a solid ionic compound conducts because it contains ions; the ions are fixed in place in the solid.
- Stating that all covalent substances are insulators; some, such as hydrogen chloride, form ions in water.
- Confusing the flow of charge with the movement of the whole substance.
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