How does the mechanism of conduction differ between a solid metal and a molten salt?

In a solid metal, charge is carried by a 'sea' of delocalised electrons that move through the fixed metal lattice. In a molten salt, the charge is carried by the physical movement of cations and anions which are free to move once the ionic lattice has been melted.

Compare the conductivity of covalent and ionic compounds in the liquid state.

Covalent compounds generally remain insulators when liquid because they consist of neutral molecules with no mobile ions or electrons. Ionic compounds become conductors when liquid (molten) because the heat energy overcomes the lattice forces, allowing ions to move and carry charge.

What is the primary difference between an electrical conductor and an insulator in terms of particle behavior?

A conductor contains charged particles (electrons or ions) that are free to move and transport energy throughout the material. An insulator lacks these mobile charged particles, either because it is made of neutral molecules or because its charged particles are locked in a rigid structure.

Why is it incorrect to say that 'solid sodium chloride conducts electricity'?

In solid sodium chloride, the sodium and chloride ions are held in a fixed, rigid 3D lattice by strong electrostatic forces. Because these ions cannot move from their positions, they cannot carry an electric current, making the solid an insulator.

What is the common mistake made when describing the flow of current through an aqueous solution?

The most common error is stating that electrons flow through the solution. In reality, electrons flow through the wires to the electrodes, but the current within the solution is maintained by the migration of ions toward the electrodes.

Can a covalent gas conduct electricity just because its particles are moving rapidly?

No, simply having mobile particles is not enough; the particles must also be charged. Most covalent gases consist of neutral molecules, so even though they move quickly, they cannot carry an electrical charge.

Define a 'Cation' and identify its behavior during conductivity.

A cation is a positively charged ion, such as $H^+$ or $Mg^{2+}$. During conductivity in an electrolyte, cations are attracted to and migrate toward the negatively charged electrode, known as the cathode.

What is an 'Anion' and where does it migrate during electrolysis?

An anion is a negatively charged ion, such as $Cl^-$ or $SO_4^{2-}$. Because it carries a negative charge, it is attracted to and migrates toward the positively charged electrode, which is called the anode.

Define 'Electrolyte' in the context of chemical conductivity.

An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water, or when melted. This conductivity is due to the presence of mobile ions produced by the dissociation of the substance.

Why does dissolving an ionic salt in water enable it to conduct electricity?

Water molecules interact with the ions in the lattice, providing enough energy to break the strong electrostatic attractions. Once dissolved, the ions are 'solvated' and can move independently throughout the solution to carry a charge.

Explaining Conductivity | Pearson Edexcel IGCSE Chemistry

1. Definition & Core Concepts

Electric Current: This is defined as the net flow of charged particles through a medium. While in metals this involves the movement of delocalised electrons, in other substances it frequently involves the movement of ions.
Charge Carriers: For a substance to conduct electricity, it must contain particles that possess an electrical charge and are free to move throughout the structure. If either of these conditions is not met, the substance acts as an insulator.
Conductivity Spectrum: Substances range from excellent conductors to high-quality insulators, depending on their bonding and physical state.

Diagram showing anions moving to the positive anode and cations moving to the negative cathode.

2. Underlying Principles

The Mobility Constraint: Even if a substance contains charged ions, it will not conduct if those ions are trapped in a rigid structure. Energy must be supplied—typically via heat or dissolution—to overcome the electrostatic forces holding the particles in place.
Covalent Neutrality: Most covalent compounds consist of neutral molecules where electrons are tightly held within shared pairs. Because there are no surplus electrons or mobile ions, these substances cannot carry a charge.
State Dependency: The physical state (solid, liquid, or gas) determines the distance and freedom of particles, which is the primary factor in whether an ionic compound can transition from an insulator to a conductor.

3. Conductivity in Covalent Compounds

Molecular Insulators: Covalent substances, such as plastic, oil, and various gases, are widely used as insulating materials. This is because their electrons are localized in bonds or lone pairs, leaving no mobile charge carriers.
Practical Applications: Because of their inability to conduct, covalent polymers are used for the protective coatings on electrical wires, ensuring that current remains contained within the metal core.
Exceptions: While most are insulators, some specific covalent structures (like graphite) are exceptions due to their unique bonding arrangements that allow for electron delocalization.

4. Conductivity in Ionic Compounds

Solid State Behavior: In solid form, ionic compounds are arranged in a giant ionic lattice. The strong electrostatic attractions between oppositely charged ions keep them in fixed positions, making them insulators.
Molten and Aqueous States: When an ionic compound is melted (molten) or dissolved in water (aqueous), the lattice structure breaks down. This allows the ions to move freely through the liquid, enabling the transport of electrical charge.
Electrolytes: A liquid or solution that contains mobile ions and can conduct electricity is known as an electrolyte. During conduction, the ions migrate toward the electrode with the opposite charge.

5. Key Distinctions

Comparison of Conduction Mechanisms

Feature	Metallic Conduction	Ionic Conduction
Charge Carriers	Delocalised Electrons	Mobile Cations and Anions
State	Solid or Liquid	Molten or Aqueous Solution
Chemical Change	No chemical change occurs	Substance is decomposed (Electrolysis)

Electron vs. Ion Flow: It is critical to distinguish that electrons do not flow through an electrolyte; instead, the physical movement of ions constitutes the current within the liquid.

6. Exam Strategy & Tips

Identify the Bonding: Always start by determining if a substance is ionic or covalent. Covalent compounds (except graphite) will almost always be insulators in your exam questions.
Check the State: If a substance is ionic, look closely at its state. If it is described as 'solid' or 'powder', it will not conduct. If it is 'molten' or 'in solution', it will conduct.
Charge Carrier Labels: When explaining why something conducts, be precise. Use the word 'electrons' for metals and 'ions' for electrolytes. Using these interchangeably is a common way to lose marks.

7. Common Pitfalls & Misconceptions

Melting vs. Dissolving: Students often confuse the two processes. Both free the ions, but melting involves heat to break the lattice, while dissolving involves water molecules pulling the lattice apart.
Electrons in Water: A very common error is stating that electrons flow through a salt solution. Electrons only travel through the external circuit and the electrodes; the 'gap' in the solution is bridged by ion migration.
Mobile Electrons in Ions: Do not claim that ionic compounds conduct because of 'delocalised electrons'. Ionic conductivity is strictly due to the movement of the ions themselves.

Explaining Conductivity

Summary

1. Definition & Core Concepts

2. Underlying Principles

3. Conductivity in Covalent Compounds

4. Conductivity in Ionic Compounds

5. Key Distinctions

6. Exam Strategy & Tips

7. Common Pitfalls & Misconceptions

Explaining Conductivity

Summary

1. Definition & Core Concepts

2. Underlying Principles

3. Conductivity in Covalent Compounds

4. Conductivity in Ionic Compounds

5. Key Distinctions

Comparison of Conduction Mechanisms

6. Exam Strategy & Tips

7. Common Pitfalls & Misconceptions

Comparison of Conduction Mechanisms