Compare ionic and covalent compounds in four properties, with one example of each. Describe one activity that shows a difference in solubility.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Open with the particles. Ionic compounds are made of ions held by strong electrostatic forces. Covalent compounds are made of neutral molecules held by weak intermolecular forces.
2 · State and melting point. Ionic: crystalline solids with high melting points (NaCl, 1074 K). Covalent: gases, liquids or soft solids with low melting points (naphthalene, 353 K).
3 · Conductivity. Ionic: conduct when molten or dissolved. Covalent: do not conduct, as there are no ions.
4 · Solubility. Ionic: soluble in water, not in organic solvents. Covalent: soluble in organic solvents such as alcohol, usually not in water.
5 · Activity. Shake iodine crystals with ethyl alcohol and with water. The alcohol turns dark brown; very little iodine dissolves in water.
6 · Real life. Tincture of iodine, used on cuts, is iodine dissolved in alcohol.
7 · Close in one line. So the type of bond decides the properties of a compound.
Scoring tip: Set out the comparison as a two-column table. Examiners find each point quickly and give marks row by row.
