Secondary 3 Chemistry Periodic Table Quiz

Secondary 3 Chemistry Quiz - Periodic Table - ANSWER KEY

Total Marks: 40

Section A: Multiple Choice (10 marks)

1. C. Chlorine Chlorine is in Group 17, the halogens. Sodium (Group 1), magnesium (Group 2), and argon (Group 18) are not halogens. [1 mark]

2. B. Group 2, Period 3 Electronic configuration 2,8,2 indicates 3 electron shells (Period 3) and 2 valence electrons (Group 2). [1 mark]

3. C. Atomic radius decreases because the nuclear charge increases and electrons are added to the same shell. Across Period 3, electrons are added to the same shell (n=3) while the number of protons increases, causing greater electrostatic attraction and pulling electrons closer to the nucleus. [1 mark]

4. A. Group 1 X₂O means two atoms of X combine with one oxygen atom. Oxygen has a charge of 2−, so each X must have a charge of 1+. Group 1 elements form 1+ ions. [1 mark]

5. B. They form coloured compounds. Transition elements form coloured compounds due to partially filled d-orbitals. Group 1 metals form white or colourless compounds. Both are good conductors, solid at room temperature (except caesium which melts near room temperature), and react with water. [1 mark]

Section B: Short Answer (10 marks)

6. A period is a horizontal row in the Periodic Table. Elements in the same period have the same number of electron shells. Award 1 mark for correct definition mentioning horizontal row OR same number of electron shells. [1 mark]

7. (a) Liquid. Bromine is the only non-metallic element that is liquid at room temperature. Accept "liquid" only. [1 mark]

(b) Bromine is less reactive than chlorine. Down Group 17, the number of electron shells increases, so the valence shell is further from the nucleus. The electrostatic attraction between the nucleus and an incoming electron decreases, making it harder for bromine to gain an electron compared to chlorine. Therefore, reactivity decreases down the group. Award 1 mark for stating bromine is less reactive. Award 1 mark for explanation referencing increased electron shells/decreased attraction for electrons. [2 marks]

8. (a) Protons: 19, Neutrons: 20, Electrons: 19 Proton number = 19 (from subscript). Neutrons = 39 − 19 = 20. Electrons = protons in a neutral atom = 19. Award 1 mark for correct protons and electrons. Award 1 mark for correct neutrons. [2 marks]

(b) Group: 1, Period: 4 Electronic configuration of K is 2,8,8,1. One valence electron = Group 1. Four electron shells = Period 4. [1 mark]

9. Noble gases are unreactive because they have a full valence (outer) electron shell. This stable electronic configuration means they do not need to gain, lose, or share electrons to achieve stability. Therefore, they rarely form chemical bonds. Award 1 mark for stating full valence shell/stable octet. Award 1 mark for explaining this means no tendency to gain/lose/share electrons. [2 marks]

10. Argon is used to provide an inert atmosphere for welding / in light bulbs to prevent the filament from oxidising / in food packaging to prevent spoilage. Accept any valid use of argon that relates to its unreactivity. Award 1 mark. [1 mark]

Section C: Structured Questions (20 marks)

11. (a) Metallic character decreases across Period 3. Sodium, magnesium, and aluminium are metals with good electrical conductivity, while silicon, phosphorus, sulfur, and chlorine are non-metals with poor electrical conductivity. The melting points also show a general change from metallic to non-metallic properties. Award 1 mark for stating metallic character decreases. Award 1 mark for using data from the table (conductivity or melting point) to support the answer. [2 marks]

(b) Silicon has a giant covalent structure with strong covalent bonds between silicon atoms in a three-dimensional network. A large amount of energy is required to break these strong covalent bonds, so silicon has a very high melting point. Phosphorus exists as simple P₄ molecules held together by weak van der Waals forces between molecules. Only a small amount of energy is required to overcome these weak intermolecular forces, so phosphorus has a low melting point. Award 1 mark for identifying silicon's giant covalent structure. Award 1 mark for explaining strong covalent bonds require much energy to break. Award 1 mark for identifying phosphorus as simple molecular with weak intermolecular forces. [3 marks]

(c) Sodium has a metallic structure consisting of positive sodium ions arranged in a lattice surrounded by a "sea" of delocalised electrons. These delocalised electrons are free to move throughout the structure and carry electric charge, so sodium conducts electricity. Chlorine exists as Cl₂ molecules with covalent bonds. All electrons are held in fixed positions within the molecules or in covalent bonds. There are no free-moving charged particles (ions or electrons), so chlorine does not conduct electricity. Award 1 mark for describing sodium's metallic bonding with delocalised electrons. Award 1 mark for explaining delocalised electrons carry charge. Award 1 mark for explaining chlorine has no free-moving charged particles. [3 marks]

12. (a) Chlorine (Cl). Electronic configuration 2,8,7 corresponds to atomic number 17, which is chlorine. [1 mark]

(b) Group: 17, Period: 3 Seven valence electrons = Group 17. Three electron shells = Period 3. [1 mark]

(c) (i)

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Award 1 mark for correct valence electrons shown. Award 1 mark for correct shared pair and lone pairs. [2 marks]

(ii) Covalent bonding. HY is hydrogen chloride (HCl), which has a covalent bond formed by sharing electrons. [1 mark]

(iii) The solution will have a low pH (acidic, pH < 7). Hydrogen chloride gas dissolves in water to form hydrochloric acid, which ionises to produce H⁺ ions, making the solution acidic. Award 1 mark for stating acidic/low pH. Award 1 mark for explaining formation of H⁺ ions in solution. [2 marks]

13. (a) Potassium floats on the water surface, moves rapidly, melts into a silvery ball, produces a hissing/effervescence sound, and burns with a lilac flame. The solution formed turns universal indicator purple/blue (alkaline). Award 1 mark for at least two correct observations (floating, moving, melting, effervescence). Award 1 mark for flame colour OR alkaline solution. [2 marks]

(b) 2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g) Award 1 mark for correct formulae. Award 1 mark for correct balancing and state symbols. [2 marks]

(c) Potassium is more reactive than sodium because potassium has one more electron shell than sodium. The valence electron in potassium is further from the nucleus, so the electrostatic attraction between the nucleus and the valence electron is weaker. Less energy is required to remove the valence electron from potassium, so it reacts more readily and vigorously. Award 1 mark for stating potassium has more electron shells. Award 1 mark for explaining valence electron is further from nucleus. Award 1 mark for explaining weaker attraction means electron is lost more easily. [3 marks]

14. (a) The d-block / central block / between Groups 2 and 13. Accept any of these answers. Award 1 mark. [1 mark]

(b) Reactants: Nitrogen (N₂) and Hydrogen (H₂) Product: Ammonia (NH₃) Award 1 mark for both reactants correct. Award 1 mark for product correct. [2 marks]

(c) (i) Water (H₂O). Copper(II) sulfate is hydrated (CuSO₄·5H₂O). Heating drives off water of crystallisation. [1 mark]

(ii) Copper(II) sulfate is coloured because copper is a transition element with partially filled d-orbitals. Electrons in these d-orbitals can absorb visible light and move between energy levels, producing the blue colour. Sodium is a Group 1 metal with no partially filled d-orbitals, so sodium sulfate does not absorb visible light and appears white. Award 1 mark for linking colour to partially filled d-orbitals in transition elements. Award 1 mark for explaining sodium has no partially filled d-orbitals. [2 marks]

15. (a) Elements in the same group have the same number of valence electrons, which determines their chemical properties. Award 1 mark for stating same number of valence electrons. [1 mark]

(b) Alkali metals. Award 1 mark for correct name. [1 mark]

(c) Melting points decrease down Group 1 from lithium to potassium. Award 1 mark for stating melting points decrease. [1 mark]

Section D: Data Analysis and Application (10 marks)

16. (a) W, X, Z, Y (least reactive to most reactive). Award 1 mark for correct order. [1 mark]

(b) Lilac flame. Award 1 mark for correct flame colour. [1 mark]

(c) Metal W is likely copper (or silver, gold, platinum). Copper is unreactive and does not react with cold water. It is below hydrogen in the reactivity series. Award 1 mark for identifying a suitable unreactive metal. Award 1 mark for explaining it does not react with cold water due to low reactivity. [2 marks]

17. (a) Element R is a noble gas. It has a full valence shell (8 electrons in the outer shell), which is a stable electronic configuration. Award 1 mark for identifying R and giving reason of full valence shell. [1 mark]

(b) Elements P (2,1) and Q (2,8,7) would react to form an ionic compound. P has 1 valence electron and tends to lose it to achieve a stable configuration, forming a 1+ ion. Q has 7 valence electrons and tends to gain 1 electron to achieve a stable octet, forming a 1− ion. The transfer of an electron from P to Q results in ionic bonding. Award 1 mark for identifying P and Q. Award 1 mark for explaining electron transfer (P loses 1 electron, Q gains 1 electron). [2 marks]

(c) PQ (or LiCl if elements are identified as lithium and chlorine). Award 1 mark for correct formula based on 1:1 ratio. [1 mark]

18. (a) Carbon has the highest melting point in Period 2. Carbon (as diamond or graphite) has a giant covalent structure with strong covalent bonds between carbon atoms throughout the structure. A very large amount of energy is required to break these strong covalent bonds, resulting in a very high melting point. Award 1 mark for identifying carbon. Award 1 mark for explaining giant covalent structure and strong covalent bonds. [2 marks]

(b) Neon has a very low melting point because it exists as individual atoms (monatomic) held together by very weak van der Waals forces. Only a small amount of energy is required to overcome these weak forces. Award 1 mark for explaining weak intermolecular forces between atoms. [1 mark]

19. (a) Halogens. Award 1 mark for correct term. [1 mark]

(b) Colour intensity increases down Group 17 (chlorine is pale green-yellow, bromine is red-brown, iodine is dark grey/purple-black). Award 1 mark for stating colour intensity increases. [1 mark]

(c) (i) The solution turns from colourless to orange/brown (or yellow-brown). Award 1 mark for correct colour change. [1 mark]

(ii) Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq) Award 1 mark for correct balanced equation. [1 mark]

(iii) Chlorine is more reactive than bromine. Chlorine, being higher up Group 17, can displace bromine from its compound because it has a greater tendency to gain electrons. Award 1 mark for stating chlorine is more reactive OR explaining relative reactivity. [1 mark]

20. (a) 2 valence electrons. Group 2 elements have 2 valence electrons. Award 1 mark. [1 mark]

(b) EO (or the oxide formula based on the element, e.g., CaO if E is calcium). Group 2 elements form 2+ ions, oxide ion is 2−, so formula is 1:1. Award 1 mark. [1 mark]

(c) The oxide of element F is more basic than the oxide of element E. Down Group 2, metallic character increases, so the oxides become more basic. Element F is below element E, so it is more metallic and its oxide is more basic. Award 1 mark for stating more basic. Award 1 mark for explaining increased metallic character down the group. [2 marks]

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