Which of the following substances does not have van der Waals' forces?

1. Analyze the question Van der Waals' forces are weak intermolecular attractions (London dispersion forces, dipole-dipole forces). We need to find the substance in which these forces are absent.

2. Explain the concept

• Van der Waals' forces exist between separate molecules or atoms that are not held together by stronger bonds.
• They are found in simple molecular substances, noble gases, and between the layers of layered structures.
• A substance held together entirely by strong bonds throughout (metallic, ionic, or giant covalent) does not rely on van der Waals' forces.

3. Check each option

• A. Copper: a metal held by metallic bonding (positive ions in a sea of delocalised electrons). Its atoms are held by metallic bonds, not van der Waals' forces. ✔ none
• B. Graphite: it has strong covalent bonds within each layer, but the layers are held together by weak van der Waals' forces. This is why graphite is soft and slippery. ✘ has them
• C. Neon: a monatomic noble gas. Its atoms attract each other only by weak van der Waals' (London) forces. ✘ has them
• D. Iodine crystals: I₂ is a simple molecular solid, with I₂ molecules held together by van der Waals' forces. ✘ has them

4. Answer Copper is the only substance held together by metallic bonding rather than van der Waals' forces.

5. Exam tip Link each type of structure to its forces:

• Metals → metallic bonds
• Ionic compounds → ionic bonds
• Simple molecules and noble gases → van der Waals' forces
• Graphite → covalent bonds within layers and van der Waals' forces between layers

If the question asks "which has no van der Waals' forces", look for a metal or ionic solid.