Periodicity

27 Grade 10 Chemistry questions on Periodicity, with worked marking schemes. 27 questions are available on this topic in full.

1. Question 1

   1 mark

   Which statement correctly compares a chlorine atom with a chloride ion, Cl⁻?

   A. The ion is smaller because the extra electron is pulled in by the nucleus

   B. The ion is larger because the same nuclear charge now holds more electrons, which repel one another

   C. The ion and the atom are the same size because the number of protons is unchanged

   D. The ion is larger because an extra energy level has been added

   (1 mark)

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2. Question 2

   1 mark

   Chlorine water is added to a colourless solution of potassium bromide in a test tube and the mixture turns brown. This shows that:

   A. the bromide ions have been reduced to bromine

   B. bromine is a stronger oxidising agent than chlorine

   C. chlorine oxidises the bromide ions to bromine because chlorine is the stronger oxidising agent

   D. potassium has been displaced from the salt by chlorine

   (1 mark)

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3. Question 3

   1 mark

   Which element in period 3 has the highest first ionisation energy?

   A. Argon

   B. Chlorine

   C. Sodium

   D. Magnesium

   (1 mark)

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4. Question 4

   4 marks

   Elements A, B and C have atomic numbers 11, 13 and 16 respectively. Identify which of them forms the oxide with the highest melting point and explain your answer in terms of bonding.

   (4 marks)

   Marking scheme

   1. Element B (atomic number 13, aluminium) forms the oxide with the highest melting point (1 mk). 2. Its oxide is ionic with a giant ionic structure (1 mk). 3. The ions carry high charges (3+ and 2-) and are small, so the electrostatic forces between them are very strong (1 mk). 4. A very large amount of heat energy is needed to break these forces, unlike the oxide of C which is a simple molecular structure held by weak intermolecular forces (1 mk). [Award mark 1 only if B is named; accept the oxide of A being compared as ionic but with lower ionic charges.]

5. Question 5

   3 marks

   State two physical properties common to the Group I metals and give one reason why they are stored under paraffin oil.

   (3 marks)

   Marking scheme

   1. Any one physical property: soft / can be cut with a knife; low melting point; low density; good conductors of heat and electricity; shiny when freshly cut (1 mk). 2. A second, different physical property from the list above (1 mk). 3. They are very reactive and would react with oxygen and water vapour in the air, so paraffin keeps air and moisture away (1 mk).

6. Question 6

   1 mark

   Two elements P and Q have atomic numbers 12 and 17 respectively. The compound formed between P and Q has the formula:

   A. PQ

   B. P₂Q₃

   C. PQ₂

   D. P₂Q

   (1 mark)

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7. Question 7

   1 mark

   An element X has the electron arrangement 2.8.2. In which group and period of the periodic table is X found?

   A. Group III, period 3

   B. Group VIII, period 2

   C. Group II, period 2

   D. Group II, period 3

   (1 mark)

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8. Question 8

   4 marks

   A Grade 10 class tests the electrical conductivity of the solid elements sodium, silicon and sulphur using a simple circuit. Suggest the expected result for each element and explain the result for sodium.

   (4 marks)

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9. Question 9

   1 mark

   Which property is greatest for silicon when compared with sodium and chlorine?

   A. Melting point

   B. Electrical conductivity in the solid state

   C. Ease of losing an outermost electron

   D. Reactivity with cold water

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10. Question 10

    3 marks

    Outline three ways in which the properties of the elements change on moving across period 3 from sodium to chlorine.

    (3 marks)

    Marking scheme

    Any three, 1 mk each: 1. Atomic radius decreases. 2. Ionisation energy generally increases. 3. Character changes from metallic through metalloid to non-metallic. 4. The oxides change from basic through amphoteric to acidic. 5. Electrical conductivity falls sharply after aluminium: sodium, magnesium and aluminium are good conductors, silicon is a semiconductor, and phosphorus, sulphur and chlorine do not conduct.

11. Question 11

    3 marks

    An element Z has 19 protons. Write its electron arrangement and identify the group and period to which it belongs.

    (3 marks)

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12. Question 12

    4 marks

    Describe how the reactivity of the alkali metals changes down Group I, and account for the trend.

    (4 marks)

    Marking scheme

    1. Reactivity increases down the group, from lithium to caesium (1 mk). 2. Down the group the atomic radius increases / more energy levels are added (1 mk). 3. The outermost electron is further from the nucleus and better shielded by inner shells (1 mk). 4. Less energy is needed to remove the outermost electron (lower ionisation energy), so the metal loses it more readily and reacts faster (1 mk).

13. Question 13

    3 marks

    Magnesium ions are present in the hard water drawn from boreholes in many parts of Kenya. Explain why a magnesium ion, Mg²⁺, is much smaller than a magnesium atom.

    (3 marks)

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14. Question 14

    1 mark

    Melting points of the Group I elements decrease from lithium to caesium because down the group:

    A. the nuclear charge decreases

    B. the elements change from metals to non-metals

    C. the number of outermost electrons decreases

    D. the metallic bond becomes weaker as the atoms get larger

    (1 mark)

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15. Question 15

    3 marks

    State the basis on which elements are arranged in the modern periodic table, and explain why elements in the same group show similar chemical properties.

    (3 marks)

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16. Question 16

    1 mark

    Across period 3 from sodium to chlorine, the atomic radius decreases. The best explanation for this trend is that:

    A. the number of occupied energy levels decreases across the period

    B. the atoms lose electrons and become smaller ions

    C. the neutrons added across the period pull the shells inwards

    D. the nuclear charge increases while electrons are added to the same energy level

    (1 mark)

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17. Question 17

    2 marks

    Account for the fact that the noble gases in Group VIII are generally unreactive.

    (2 marks)

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18. Question 18

    1 mark

    A Grade 10 learner drops small pieces of lithium, sodium and potassium into separate troughs of cold water. Which observation is expected?

    A. Lithium reacts most vigorously because it has the smallest atoms

    B. Potassium reacts most vigorously because its outermost electron is lost most easily

    C. Only potassium reacts; lithium and sodium are unreactive with cold water

    D. All three react at the same rate because each has one outermost electron

    (1 mark)

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19. Question 19

    4 marks

    Distinguish between the oxides of sodium and sulphur in terms of their behaviour when each is shaken with water and the resulting solution tested with litmus paper.

    (4 marks)

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20. Question 20

    3 marks

    Chlorine gas is bubbled through a solution of potassium iodide. State what is observed and write the ionic equation for the reaction.

    (3 marks)

    Marking scheme

    1. The colourless solution turns brown / a dark brown or black solid (iodine) is formed (1 mk). 2. Ionic equation: Cl₂(g) + 2$I^{-}$(aq) → 2Cl⁻(aq) + I₂(aq/s) (1 mk for correct species, 1 mk for correct balancing and state symbols) (2 mks). [Accept the explanation that chlorine, being the stronger oxidising agent, oxidises iodide ions and displaces iodine.]

21. Question 21

    1 mark

    Which of the following oxides, when shaken with water, gives a solution that turns blue litmus paper red?

    A. Sodium oxide

    B. Sulphur(IV) oxide

    C. Magnesium oxide

    D. Calcium oxide

    (1 mark)

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22. Question 22

    1 mark

    An element Y in period 3 forms an oxide with the formula Y₂O₃ that reacts with both dilute hydrochloric acid and sodium hydroxide solution. Element Y is most likely:

    A. aluminium

    B. sodium

    C. phosphorus

    D. magnesium

    (1 mark)

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23. Question 23

    3 marks

    Explain why the first ionisation energy of magnesium is higher than that of sodium but lower than that of chlorine.

    (3 marks)

    Marking scheme

    1. Magnesium has a greater nuclear charge than sodium while its outermost electron is in the same energy level, so the electron is held more tightly and more energy is needed to remove it (1 mk). 2. Chlorine has an even greater nuclear charge than magnesium with the outermost electron still in the third energy level (1 mk). 3. The atomic radius of chlorine is smaller, so its outermost electron is closer to the nucleus and harder to remove than that of magnesium (1 mk).

24. Question 24

    3 marks

    Explain why the atomic radius decreases from sodium to chlorine across period 3.

    (3 marks)

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25. Question 25

    4 marks

    Explain, with an equation in each case, why aluminium oxide is described as an amphoteric oxide.

    (4 marks)

    Marking scheme

    1. An amphoteric oxide reacts with both acids and bases/alkalis (1 mk). 2. With acid: Al₂O₃(s) + 6HCl(aq) → 2AlCl₃$(aq)+3H$₂O(l) (1 mk). 3. With alkali: Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2NaAl(OH)₄(aq) (1 mk). 4. In both cases a salt and water are formed, so the oxide behaves as both a base and an acid (1 mk). [Accept NaAlO₂ + H₂O as the alkali product.]

26. Question 26

    1 mark

    The halogens become less reactive on moving down Group VII from chlorine to iodine. The best explanation is that down the group:

    A. the number of outermost electrons decreases

    B. the nuclear charge decreases

    C. the outermost energy level is further from the nucleus, so an electron is gained less easily

    D. the atoms become smaller, so an incoming electron is repelled

    (1 mark)

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27. Question 27

    1 mark

    Helium is placed in Group VIII (Group 0) even though it has only two outermost electrons. This is because helium:

    A. has two energy levels like the other Group VIII elements

    B. has the same atomic radius as neon

    C. has a full outermost energy level and is therefore unreactive

    D. forms compounds similar to those of neon and argon

    (1 mark)

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