Explain, with reasons, three properties of ionic compounds such as sodium chloride.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Say what they are made of. Ionic compounds are made of cations and anions held by strong electrostatic forces in a crystal lattice.
2 · Property 1: melting point.High melting and boiling points (NaCl melts at 1074 K), because much heat is needed to overcome the strong forces.
3 · Property 2: conduction. They conduct electricity when molten or in water, because the ions move. As solids they do not, because the ions are fixed.
4 · Property 3: solubility. They dissolve in water, which weakens the forces between ions, but not in organic solvents such as alcohol.
5 · Real life. Wet hands near switches are dangerous because dissolved salts from sweat conduct.
6 · Close in one line. So the strong forces between ions explain all these properties.
Scoring tip: Write the reason after each property. A property with no reason usually gets only half the mark.
