Secondary 4 Pure Chemistry Periodic Table Quiz

Secondary 4 Pure Chemistry Quiz - Periodic Table - ANSWER KEY

Total Marks: 40

Section A: Multiple Choice (10 marks)

1 mark each

1. C — Elements in the same group have similar chemical properties because they have the same number of valence electrons.

2. B — Group 1 (1 valence electron), Period 4 (4 electron shells: 2, 8, 8, 1).

3. C — Melting point decreases down Group 1 due to weaker metallic bonding as atomic radius increases.

4. B — Chlorine is a stronger oxidising agent than bromine; it oxidises Br⁻ to Br₂ while being reduced to Cl⁻.

5. C — Iron is a transition element. Calcium and aluminium are main group elements; zinc (though d-block) is not considered a transition element as it has a full d¹⁰ configuration in both atom and common ion.

6. C — Copper forms coloured compounds (e.g., blue CuSO₄) and acts as a catalyst in some reactions.

7. A — Sodium has more electron shells than lithium, so the valence electron is further from the nucleus and more easily lost.

8. C — Astatine is below iodine, so it would be a dark-coloured solid at room temperature (trend: state changes from gas → liquid → solid down Group 17). It is less reactive than iodine, so it cannot displace chlorine.

9. C — Magnesium is more reactive than iron and can provide sacrificial protection. Copper, silver, and gold are less reactive than iron.

10. D — Transition elements form ions with partially filled d-orbitals. They exhibit variable oxidation states, form coloured compounds, and are good conductors.

Section B: Structured Questions (20 marks)

11. Group 1 Metals

(a) Potassium melts into a silvery ball, moves rapidly on the water surface, burns with a lilac flame, and may explode. [1 mark] Award 1 mark for any two correct observations (melts, moves rapidly, lilac flame, possible explosion).

(b) Going down Group 1, the number of electron shells increases, so the valence electron is further from the nucleus. [1 mark] The electrostatic attraction between the nucleus and the valence electron decreases, making it easier to lose the valence electron. [1 mark]

(c) 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) [2 marks] Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols. Deduct 1 mark if state symbols are missing or incorrect.

12. Halogens

(a) Chlorine and fluorine have the same number of valence electrons (7 valence electrons). [1 mark] Elements in the same group have similar chemical properties because they have the same number of valence electrons, which determine how they react. [1 mark]

(b)(i) Iodine / I₂ [1 mark]

(b)(ii) Cl₂(aq) + 2I⁻(aq) → 2Cl⁻(aq) + I₂(aq) [2 marks] Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols.

(b)(iii) Chlorine is a stronger oxidising agent than iodine. [1 mark] Chlorine atoms gain electrons more readily than iodine atoms because chlorine has fewer electron shells, so the incoming electron is more strongly attracted to the nucleus. [1 mark] Accept: Chlorine is more reactive than iodine / Chlorine is above iodine in Group 17.

13. Transition Elements

(a) Any two from: [2 marks]

• Transition elements form coloured compounds (Group 1 metals form white/colourless compounds).
• Transition elements have variable oxidation states (Group 1 metals have only +1 oxidation state).
• Transition elements act as catalysts (Group 1 metals generally do not).
• Transition elements have higher melting points and densities. Award 1 mark each for any two correct differences.

(b)(i) Variable oxidation state / variable valency [1 mark]

(b)(ii) Fe²⁺: pale green [1 mark]; Fe³⁺: yellow-brown / reddish-brown [1 mark]

(c) Alloying introduces atoms of different sizes into the metal lattice, disrupting the regular arrangement of atoms. [1 mark] This prevents layers of atoms from sliding over each other easily, making the alloy harder and stronger. Accept any reasonable explanation referencing disruption of the metallic lattice.

14. Group 1 Melting Points

(a) The melting points of Group 1 elements decrease going down the group / as atomic number increases. [1 mark]

(b) Group 1 metals have metallic bonding with positive metal ions in a sea of delocalised electrons. [1 mark] Going down the group, the atomic radius increases, so the distance between the positive ions and delocalised electrons increases. The electrostatic attraction between them becomes weaker, so less energy is required to overcome the metallic bonds, resulting in lower melting points. [1 mark]

15. Reactivity Series

(a) Metal M is likely to be zinc or iron. [1 mark] Explanation: M does not react with cold water, so it is below calcium in the reactivity series. M reacts slowly with dilute acid, so it is above lead. M's oxide can be reduced by carbon, so M is below carbon in the reactivity series. This places M between magnesium and copper, most likely zinc or iron. [1 mark] Accept zinc or iron with correct reasoning. Award partial credit for identifying the correct region of the reactivity series.

(b) M(s) + 2HCl(aq) → MCl₂(aq) + H₂(g) [2 marks] Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols. Accept Fe or Zn in place of M.

Section C: Data-Based and Extended Response (10 marks)

16. Periodic Table Predictions

(a)(i) Sulfur / S [1 mark]

(a)(ii) The oxide of sulfur is acidic. [1 mark] Non-metals form acidic oxides. Sulfur is a non-metal in Group 16, so its oxide (SO₂ or SO₃) dissolves in water to form an acidic solution (sulfurous acid or sulfuric acid). [1 mark] Accept: SO₂ + H₂O → H₂SO₃ or SO₃ + H₂O → H₂SO₄ as supporting evidence.

17. Period 3 Trends

(a) The atomic radius decreases across Period 3. [1 mark]

(b) Across Period 3, the number of protons in the nucleus increases, so the nuclear charge increases. [1 mark] Electrons are added to the same electron shell, so the shielding effect remains approximately the same. The increased nuclear attraction pulls the electrons closer to the nucleus, resulting in a smaller atomic radius. [1 mark]

(c) Aluminium has a higher melting point than magnesium. [1 mark] Aluminium has three valence electrons per atom compared to magnesium's two, so there are more delocalised electrons in the metallic lattice. This results in stronger metallic bonding between the positive ions and the sea of delocalised electrons, requiring more energy to overcome. [1 mark] Accept: Aluminium ions have a higher charge (3+) compared to magnesium ions (2+), leading to stronger electrostatic attraction with delocalised electrons.

18. Group 17 Properties

(a) Chlorine is a greenish-yellow gas at room temperature. [1 mark]

(b) Going down Group 17, the size of the halogen molecules increases, so the number of electrons per molecule increases. [1 mark] This leads to stronger intermolecular forces of attraction (van der Waals' forces) between molecules, so more energy is required to overcome these forces, resulting in higher boiling points. [1 mark]

(c) Cl₂(aq) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq) [2 marks] Accept ionic equation: Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq). Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols.

19. Metal Extraction

(a) Aluminium is more reactive than carbon, so it cannot be extracted by reduction with carbon. [1 mark] Electrolysis must be used to reduce aluminium ions. Iron is less reactive than carbon, so carbon can reduce iron(III) oxide to iron. [1 mark]

(b) Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g) [2 marks] Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols.

(c) Any one from: [1 mark]

• Production of carbon dioxide contributes to global warming / climate change.
• Carbon monoxide is a toxic / poisonous gas.
• Quarrying for raw materials damages the environment.
• Acid rain from sulfur dioxide emissions (if sulfur impurities are present).

20. Unknown Element Y

(a) Element Y is a metal. [1 mark] It forms a basic oxide, which is a characteristic property of metals. [1 mark] Accept: It conducts electricity and reacts with acid to produce hydrogen gas.

(b) Element Y could be iron or zinc. [1 mark] It reacts slowly with dilute hydrochloric acid, suggesting it is not a very reactive metal like potassium or sodium. It forms a basic oxide and conducts electricity, confirming it is a metal. Its slow reaction with acid places it in the middle of the reactivity series, such as iron or zinc. [1 mark] Accept any reasonable suggestion with justification.

(c) Y(s) + 2HCl(aq) → YCl₂(aq) + H₂(g) [2 marks] Award 1 mark for correct formulae, 1 mark for correct balancing and state symbols. Accept Fe or Zn in place of Y.

END OF ANSWER KEY