STUDENT SPACE · TOPIC 6

Ionic and molecular properties

Use structure, attractions and mobile charged particles to explain properties.

The essentials

Ionic lattices have high melting points because much energy is needed to overcome strong electrostatic attractions.
Ionic substances conduct when molten or dissolved because their ions can move. Solid ions stay in fixed positions.
Simple molecular substances usually have low melting and boiling points because intermolecular forces are weak. Melting does not break their covalent bonds.

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Which charged particles carry current in molten sodium chloride?

Need a hint for Question 1?

Ionic conduction involves movement of ions.

Check Question 1

Mobile sodium and chloride ions.

Explain why solid MgO cannot conduct but molten MgO can.

Need a hint for Question 2?

Conduction needs charged particles that can move.

Check Question 2

In solid MgO the ions are fixed. In molten MgO the ions are mobile and carry charge.

Water boils without breaking its O–H covalent bonds. Explain what is overcome.

Need a hint for Question 3?

Distinguish attractions between molecules from bonds within them.

Check Question 3

Intermolecular forces between water molecules are overcome.

Use the matching chapter worksheet. Attempt independently, compare your reasoning with your partner, then bring unresolved questions to your teacher.