A-Level Chemistry: Periodicity, Group 2 and Group 7
Inorganic trend questions are the most pattern-rich territory in A-Level Chemistry: the marks go to those who can both state the trend and explain the structure behind it. This quiz covers Period 3, Group 2 and Group 7 — the three trend systems every specification examines.
The Period 3 questions target the explanations rather than the bare facts: why silicon's melting point towers over phosphorus's (giant covalent lattice against simple P₄ molecules), and both canonical ionisation-energy dips — magnesium to aluminium (the 3p electron above 3s) and phosphorus to sulfur (paired-electron repulsion) — each tested through its reason, with the electron configurations given in the question so the reasoning is the skill.
The Group 2 questions cover the down-group trends that must be kept straight in pairs: hydroxide solubility rising while sulfate solubility falls, and the practical chemistry hanging off them, with magnesium hydroxide's antacid role as the applied example.
Group 7 gets the fullest treatment: boiling points rising with van der Waals strength, electronegativity falling with radius, oxidising power demonstrated through displacement (chlorine turning potassium bromide solution orange), the silver nitrate/ammonia halide identification scheme, and both chlorine disproportionations — in water to HCl and HClO, and in cold dilute sodium hydroxide to chloride and chlorate(I), with the oxidation-state bookkeeping (0 to −1 and +1 simultaneously) made explicit.
Explanations consistently follow the state-the-trend, name-the-cause structure that inorganic mark schemes reward.
- Explain Period 3 melting point and ionisation energy patterns structurally
- Keep Group 2 hydroxide and sulfate solubility trends straight
- Rank halogen oxidising power and predict displacement outcomes
- Apply the silver nitrate and ammonia halide identification scheme
- Track oxidation states through chlorine's disproportionation reactions
Aligned to the inorganic core of the DfE A level science subject content: periodicity across Period 3, Group 2 trends and uses, and Group 7 oxidising ability, tests and disproportionation.
Sample question
The bar chart shows the melting points of the Period 3 elements. Why does the melting point of Silicon (Si) significantly exceed that of Phosphorus (P4) in Period 3?
- Silicon has a giant covalent lattice structure
- Phosphorus has stronger metallic bonding
- Silicon atoms are held by weak van der Waals forces
- Phosphorus has a higher molar mass
See the answer
Silicon has a giant covalent lattice structure
Silicon forms a giant covalent lattice with strong covalent bonds requiring high energy to break, whereas Phosphorus exists as small P4 molecules held together by weak van der Waals forces.
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