OCR A-Level Chemistry Periodic table, elements and physical chemistry (01), June 2019: Question 7

✅ Correct Answer: A (S, Si, Al)

Option A is the correct choice because:

• S (Sulfur) exists as S₈ molecules in a simple molecular lattice.
• Si (Silicon) forms a tetrahedral network in a giant covalent lattice.
• Al (Aluminium) consists of positive ions in a sea of delocalised electrons, forming a giant metallic lattice.

💡 Key Knowledge

• Metals (Na, Mg, Al): Giant metallic lattices with strong electrostatic attractions between positive ions and delocalised electrons.
• Metalloids (Si): Giant covalent macromolecular structure (similar to diamond).
• Non-metals (P₄, S₈, Cl₂): Simple molecular lattices held together by weak intermolecular London forces.
• Noble gases (Ar): Monatomic simple molecular structure.

🧠 Exam Technique

Tackle multiple-choice questions involving lists by evaluating them one structure at a time:

• Scan the options and cross out any containing elements that do not match the requested category.
• Recall the trend in melting points across Period 3 to jog your memory on bonding types.

❌ Common Errors

• Confusing Phosphorus (P) and Sulfur (S): Both are simple molecular, but students often mix up their molecular formulas (P₄ vs S₈) or misclassify them as giant structures due to high relative molecular masses.
• Misidentifying Silicon: Assuming silicon is metallic because it is a semi-conductor/metalloid, rather than recognising its giant covalent macromolecular structure.