Secondary 4 Pure Chemistry Periodic Table Quiz

Secondary 4 Pure Chemistry Quiz - Periodic Table - ANSWER KEY

Total Marks: 40

Section A: Multiple Choice Questions (5 marks)

1. C. Iron

• Explanation: Iron is a transition element located in the d-block of the Periodic Table. Sodium and calcium are Group 1 and Group 2 metals respectively. Aluminium is a Group 13 metal. Transition elements are characterised by having partially filled d-orbitals and exhibit properties such as variable oxidation states, coloured compounds, and catalytic activity.
• Marking: 1 mark for correct answer.

2. C. Melting point

• Explanation: Going down Group 1, atomic radius increases, reactivity with water increases, and density generally increases. However, melting point decreases down the group due to weaker metallic bonding as the atoms get larger and the delocalised electrons are further from the positive ion cores.
• Marking: 1 mark for correct answer.

3. B. Group 17, Period 3

• Explanation: The electronic configuration 2, 8, 7 shows three occupied electron shells, so the element is in Period 3. There are 7 valence electrons, so the element is in Group 17 (or Group VII). Note: Both Group 17 and Group VII are accepted in O-Level, but Group 17 is the modern IUPAC designation.
• Marking: 1 mark for correct answer.

4. B. Reactivity decreases because the atoms get larger.

• Explanation: Halogens react by gaining one electron to form halide ions. Down Group 17, the atoms get larger, meaning the outermost shell is further from the nucleus. The attraction between the nucleus and an incoming electron decreases, making it harder to gain an electron. Therefore, reactivity decreases down the group.
• Marking: 1 mark for correct answer.

5. D. Sulfur

• Explanation: Metallic elements (sodium, magnesium, aluminium) form basic or amphoteric oxides. Non-metallic elements form acidic oxides. Sulfur is a non-metal in Group 16 and forms acidic oxides such as SO₂ and SO₃, which dissolve in water to form sulfurous acid and sulfuric acid respectively.
• Marking: 1 mark for correct answer.

Section B: Structured Questions (10 marks)

6. (a) Element P is sodium (Na). [0.5 mark] Its electronic configuration is 2, 8, 1, which means it has one valence electron. This is characteristic of Group 1 elements. [0.5 mark]

• Total: 1 mark

(b) Element Q belongs to Group 17 / Group VII / the halogens. [1 mark]

• Total: 1 mark

(c) Element R has the electronic configuration 2, 8, 8, which is a full outer shell (octet) / noble gas configuration. [0.5 mark] Atoms with a full valence shell are stable and do not need to gain, lose, or share electrons, so they are chemically unreactive / inert. [0.5 mark]

• Total: 1 mark

7. (a) 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)

• Marking: 1 mark for correct formulae, 1 mark for correct state symbols. Accept KOH or K⁺ + OH⁻.
• Total: 2 marks

(b) Any two of the following (0.5 mark each):

• Potassium floats on the water surface
• Potassium melts into a silvery ball
• Potassium moves rapidly across the water surface
• Potassium burns with a lilac/purple flame
• Effervescence / fizzing / bubbles of gas produced
• Heat is released (the reaction is exothermic)
• Total: 1 mark

(c) Potassium reacts vigorously / violently with oxygen and water vapour in the air. [0.5 mark] Storing it under oil prevents contact with air and moisture. [0.5 mark]

• Total: 1 mark

8. (a) Bromine is a reddish-brown liquid at room temperature. [1 mark]

• Total: 1 mark

(b)(i) Displacement reaction / redox reaction. [1 mark]

• Total: 1 mark

(b)(ii) Cl₂(aq) + 2Br⁻(aq) → 2Cl⁻(aq) + Br₂(aq)

• Marking: 1 mark for correct ionic equation. Accept with state symbols or without. The key is showing chlorine displacing bromide ions.
• Total: 1 mark

Section C: Data-Based and Extended Response Questions (20 marks)

9. (a) Approximately 1410°C (accept 1400–1420°C based on graph reading). [1 mark]

• Total: 1 mark

(b) Silicon has a giant covalent / giant molecular structure. [0.5 mark] Each silicon atom is covalently bonded to four other silicon atoms in a tetrahedral arrangement, forming a continuous three-dimensional network. [0.5 mark] A large amount of energy is required to break the many strong covalent bonds throughout the structure. [0.5 mark] Therefore, silicon has a very high melting point. [0.5 mark]

• Total: 2 marks

(c) Sodium, magnesium, and aluminium are all metals with metallic bonding. [0.5 mark] Across Period 3 from sodium to aluminium, the number of valence electrons contributed to the 'sea of delocalised electrons' increases (Na: 1, Mg: 2, Al: 3). [1 mark] The charge on the positive metal ions also increases (Na⁺, Mg²⁺, Al³⁺). [0.5 mark] The greater number of delocalised electrons and the higher ionic charge result in stronger electrostatic forces of attraction between the positive ions and the sea of delocalised electrons. [0.5 mark] More energy is required to overcome these stronger metallic bonds, so the melting point increases. [0.5 mark]

• Total: 3 marks

(d) Phosphorus, sulfur, chlorine, and argon exist as simple molecular structures / simple covalent molecules (P₄, S₈, Cl₂, Ar). [0.5 mark] The atoms within each molecule are held together by strong covalent bonds, but the forces of attraction between the molecules (intermolecular forces / van der Waals' forces) are weak. [1 mark] Only a small amount of energy is required to overcome these weak intermolecular forces, so these substances have low melting points. [0.5 mark]

• Total: 2 marks

10. (a) Element A is aluminium (Al). [0.5 mark] An amphoteric oxide is an oxide that can react with both acids and alkalis/bases to form a salt and water. [0.5 mark] For example, aluminium oxide reacts with hydrochloric acid to form aluminium chloride and water, and with sodium hydroxide to form sodium aluminate and water. [0.5 mark for either example or general explanation]

• Total: 2 marks (accept 2 marks if both identification and explanation are correct)

(b) Any two of the following (1 mark each):

• Transition elements have variable oxidation states (e.g., iron forms Fe²⁺ and Fe³⁺), while Group 1 metals have only +1 oxidation state.
• Transition elements form coloured compounds (e.g., copper(II) sulfate is blue, iron(II) sulfate is green), while Group 1 compounds are usually white or colourless.
• Transition elements and their compounds act as catalysts (e.g., iron in the Haber Process, manganese(IV) oxide in decomposition of hydrogen peroxide), while Group 1 metals generally do not.
• Transition elements have higher melting points and densities than Group 1 metals.
• Transition elements are less reactive than Group 1 metals.
• Total: 2 marks

(c)(i) Ionic bonding / electrovalent bonding. [1 mark]

• Total: 1 mark

(c)(ii) Dot-and-cross diagram showing:

• D (Group 1) loses one electron to form D⁺ with no valence electrons shown (or a full outer shell of 8 from the previous shell).
• F (Group 17) gains one electron to form F⁻ with 8 valence electrons (dots and crosses).
• Both ions enclosed in square brackets with charges shown.
• D⁺ shown with dots, F⁻ shown with crosses (or vice versa, but consistent notation).
• Marking: 1 mark for correct electron transfer representation, 1 mark for correct ion charges and brackets.
• Total: 2 marks

(d)(i) Element E is in Period 3. [0.5 mark] Its electronic configuration is 2, 8, 3, which shows three occupied electron shells. The Period number corresponds to the number of occupied electron shells. [0.5 mark]

• Total: 1 mark

(d)(ii) E₂C₃ or Al₂O₃ (since E is aluminium, Group 13, forming Al³⁺; C is oxygen, Group 16, forming O²⁻). [1 mark]

• Total: 1 mark

11. (a) Copper < Zinc < Magnesium < Potassium (increasing reactivity) [1 mark]

• Total: 1 mark

(b)(i) Any two of the following (0.5 mark each):

• The zinc metal dissolves / becomes smaller.
• A reddish-brown / pink solid (copper) deposits on the zinc or appears in the solution.
• The blue colour of the copper(II) sulfate solution fades / becomes colourless.
• Heat is released (the reaction is exothermic).
• Total: 1 mark

(b)(ii) Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

• Marking: 1 mark for correct ionic equation. State symbols are not required but accepted.
• Total: 1 mark

(b)(iii) Zinc atoms lose electrons to form Zn²⁺ ions (oxidation). [0.5 mark] Copper(II) ions gain electrons to form copper atoms (reduction). [0.5 mark] Since both oxidation and reduction occur simultaneously, this is a redox reaction. [1 mark]

• Total: 2 marks

(c) Aluminium reacts with oxygen in the air to form a thin, strong, and impervious layer of aluminium oxide (Al₂O₃) on its surface. [1 mark] This oxide layer is firmly attached and prevents further reaction of the underlying aluminium with air and water, making it resistant to corrosion. [0.5 mark] Iron, on the other hand, forms rust (hydrated iron(III) oxide) which is flaky and porous, exposing fresh iron to further corrosion. [0.5 mark]

• Total: 2 marks

12. (a) Electrical conductivity decreases across Period 3. [0.5 mark] Sodium, magnesium, and aluminium are metals with metallic bonding; they have a 'sea' of delocalised electrons that can move freely and carry charge, making them good conductors. [1 mark] Silicon is a metalloid/semi-conductor with a giant covalent structure; it has limited electrical conductivity. [0.5 mark] Phosphorus, sulfur, and chlorine are non-metals with simple molecular structures; they have no free-moving charged particles (electrons or ions), so they are poor conductors. [1 mark]

• Total: 3 marks

(b) Argon is a poor conductor of electricity / non-conductor. [0.5 mark] Argon exists as individual atoms (monatomic) with a full outer shell of electrons; there are no delocalised electrons or ions free to move and carry charge. [0.5 mark]

• Total: 1 mark

Section D: Challenge Questions (5 marks)

13. (a) Moles of H₂ = Volume / Molar volume = (240 / 1000) dm³ / 24.0 dm³ mol⁻¹ = 0.240 dm³ / 24.0 dm³ mol⁻¹ = 0.0100 mol. [1 mark]

• Total: 1 mark

(b) From the equation, 2 mol X produces 1 mol H₂. Moles of X = 2 × moles of H₂ = 2 × 0.0100 = 0.0200 mol. [1 mark]

• Total: 1 mark

(c) Relative atomic mass of X = mass / moles = 0.460 g / 0.0200 mol = 23.0 g mol⁻¹. [1 mark]

• Total: 1 mark

(d) Element X is sodium (Na). [0.5 mark] The relative atomic mass of sodium is 23.0, which matches the calculated value. Sodium is in Group 1 of the Periodic Table. [0.5 mark]

• Total: 1 mark

(e) Any one of the following (1 mark):

• Soft / can be cut with a knife. Sodium has only one valence electron per atom contributing to the metallic bonding, resulting in weak metallic bonds and a soft metal.
• Low melting point. The metallic bonding in sodium is relatively weak due to the single valence electron and large atomic radius, requiring less energy to overcome.
• Good conductor of electricity. Sodium has delocalised electrons that are free to move and carry charge.
• Low density. Sodium atoms are relatively large and the metallic bonding is weak, resulting in a less closely packed structure.
• Total: 1 mark

14. (a) Yellow-green / greenish-yellow. [1 mark]

• Total: 1 mark

(b) 2, 8, 7 (since it is in Group 17 and Period 3). [1 mark]

• Total: 1 mark

(c) H₂(g) + Y₂(g) → 2HY(g) or H₂(g) + Cl₂(g) → 2HCl(g). [1 mark]

• Total: 1 mark

(d) The blue litmus paper turns red. [0.5 mark] The compound (HCl) dissolves in water to form an acidic solution (hydrochloric acid). [0.5 mark]

• Total: 1 mark

(e) Y₂ (chlorine) is less reactive than fluorine because chlorine atoms are larger than fluorine atoms. [0.5 mark] The outermost shell of chlorine is further from the nucleus, so the attraction between the nucleus and an incoming electron is weaker. It is harder for chlorine to gain an electron compared to fluorine. [0.5 mark]

• Total: 1 mark

15. (a) Sodium (Na) has the largest atomic radius. [0.5 mark] Across Period 3, the number of protons increases, increasing the nuclear charge. The electrons are added to the same shell, so the shielding effect remains similar. The increased nuclear attraction pulls the electrons closer, decreasing the atomic radius. Sodium, being the first element, has the fewest protons and weakest nuclear attraction. [0.5 mark]

• Total: 1 mark

(b) Sodium forms a basic oxide (Na₂O) or magnesium forms a basic oxide (MgO). [0.5 mark] Equation: Na₂O(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) OR MgO(s) + 2HCl(aq) → MgCl₂(aq) + H₂O(l). [1 mark for correct formulae, 0.5 mark for correct balancing and state symbols]

• Total: 2 marks

(c) Argon has a full outer shell of electrons (octet) / stable electronic configuration. [0.5 mark] It does not need to gain, lose, or share electrons to achieve stability, so it is chemically inert / unreactive. [0.5 mark]

• Total: 1 mark

(d) Any one of the following (1 mark):

• High melting point / boiling point (due to strong covalent bonds throughout the giant structure requiring a lot of energy to break).
• Hard (due to the rigid three-dimensional network of strong covalent bonds).
• Insoluble in water (giant covalent structures are generally insoluble).
• Poor conductor of electricity (no delocalised electrons or free ions; electrons are fixed in covalent bonds).
• Total: 1 mark

16. (a) None of the elements is a noble gas. (Accept: There is no noble gas among W, X, Y, Z. A noble gas would have a full outer shell of 8 electrons, e.g., 2, 8 or 2, 8, 8.) [1 mark]

• Total: 1 mark

(b) X and Y would form XY₂. [0.5 mark] X has electronic configuration 2, 8, 2, so it is in Group 2 and forms X²⁺ ions. Y has electronic configuration 2, 8, 7, so it is in Group 17 and forms Y⁻ ions. [0.5 mark] To balance charges, one X²⁺ ion combines with two Y⁻ ions, giving the formula XY₂. [1 mark]

• Total: 2 marks

(c) Z is more reactive than W. [0.5 mark] Both are in Group 1. Z has electronic configuration 2, 8, 18, 8, 1, so it is lower down the group than W (2, 1). [0.5 mark] Reactivity increases down Group 1 because the valence electron is further from the nucleus and more easily lost. The increased shielding and larger atomic radius outweigh the increased nuclear charge. [1 mark]

• Total: 2 marks

17. (a) Atomic number is the number of protons in the nucleus of an atom. [1 mark]

• Total: 1 mark

(b) Elements in the same group have the same number of valence electrons. [0.5 mark] Chemical properties are determined by the number of valence electrons, so elements in the same group undergo similar reactions. [0.5 mark]

• Total: 1 mark

(c)(i) Element J (atomic number 12): 2, 8, 2. [1 mark]

• Total: 1 mark

(c)(ii) J is in Group 2 (Mg), K is in Group 17 (Cl). Formula: JCl₂ or MgCl₂. [1 mark]

• Total: 1 mark

(c)(iii) Ionic bonding / electrovalent bonding. [1 mark]

• Total: 1 mark

18. (a) Atomic radius decreases across Period 3. [1 mark]

• Total: 1 mark

(b) Across Period 3, the number of protons in the nucleus increases (increasing nuclear charge). [0.5 mark] Electrons are added to the same outer shell, so the shielding effect from inner shells remains approximately constant. [0.5 mark] The increased nuclear charge attracts the electrons more strongly, pulling the outer shell closer to the nucleus. [0.5 mark] Therefore, the atomic radius decreases. [0.5 mark]

• Total: 2 marks

(c) Argon has a slightly larger atomic radius than chlorine because argon has a full outer shell (octet) of electrons. [0.5 mark] In argon, the electron-electron repulsion between the paired electrons in the 3p orbitals is greater than in chlorine, which has an unpaired electron. [0.5 mark] This increased repulsion causes the electron cloud to expand slightly, resulting in a larger atomic radius. [1 mark]

• Total: 2 marks

19. (a) Any two of the following (0.5 mark each):

• Soft / can be cut with a knife
• Low density (some float on water)
• Low melting and boiling points (compared to other metals)
• Good conductors of electricity and heat
• Shiny when freshly cut
• Total: 1 mark

(b) 4Li(s) + O₂(g) → 2Li₂O(s). [1 mark]

• Total: 1 mark

(c) Reactivity increases down Group 1. [0.5 mark] Down the group, the atomic radius increases and the number of inner electron shells increases (increased shielding). [0.5 mark] The valence electron is further from the nucleus and experiences weaker electrostatic attraction. [0.5 mark] It is easier to lose the valence electron, so reactivity increases. [0.5 mark]

• Total: 2 marks

(d) Any one of the following (1 mark):

• Wear safety goggles / eye protection. Sodium reacts violently with water and may spit, posing a risk to eyes.
• Use a small piece of sodium. A large piece could react too vigorously and cause an explosion.
• Keep a safe distance / use tongs. To avoid contact with the corrosive sodium hydroxide formed and the heat released.
• Perform the reaction behind a safety screen. To protect from splashes or explosions.
• Total: 1 mark

20. (a) Iodine is a greyish-black / dark purple solid at room temperature. [1 mark]

• Total: 1 mark

(b) Boiling points increase down Group 17. [0.5 mark] Down the group, the size of the halogen molecules (X₂) increases, and the number of electrons increases. [0.5 mark] The intermolecular forces of attraction (van der Waals' forces) between the molecules become stronger. [0.5 mark] More energy is required to overcome these stronger intermolecular forces, so the boiling point increases. [0.5 mark]

• Total: 2 marks

(c) Chlorine is added to drinking water to kill bacteria / disinfect / sterilise the water, making it safe to drink. [1 mark]

• Total: 1 mark

(d) Cl₂(aq) + 2I⁻(aq) → 2Cl⁻(aq) + I₂(aq). [1 mark]

• Total: 1 mark

END OF ANSWER KEY