Chemical Bonding

28 Grade 10 Chemistry questions on Chemical Bonding, with worked marking schemes. 28 questions are available on this topic in full.

1. Question 1

   2 marks

   Distinguish between an ionic bond and a covalent bond.

   (2 marks)

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2. Question 2

   1 mark

   A learner finds that a solid melts at 45 degrees Celsius, does not conduct electricity either as a solid or when melted, and dissolves in paraffin but not in water. The solid is most likely to have a

   A. giant covalent structure

   B. simple molecular structure

   C. giant ionic structure

   D. giant metallic structure

   (1 mark)

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3. Question 3

   1 mark

   Which pair of elements is most likely to combine to form a compound containing ionic bonds?

   A. Potassium and bromine

   B. Phosphorus and hydrogen

   C. Nitrogen and chlorine

   D. Carbon and sulphur

   (1 mark)

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4. Question 4

   1 mark

   Aluminium used for roofing sheets is extracted from its oxide. Aluminium forms Al3+ ions and oxygen forms O2- ions. The formula of aluminium oxide is

   A. Al2O3

   B. Al3O2

   C. AlO

   D. AlO2

   (1 mark)

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5. Question 5

   3 marks

   Water boils at 100 degrees Celsius while hydrogen sulphide, which has a larger relative molecular mass, boils at about -60 degrees Celsius. Explain this difference.

   (3 marks)

   Marking scheme

   Oxygen is much more electronegative than sulphur, so the O-H bond is strongly polar and water molecules are attracted to one another by hydrogen bonds (1 mark). Hydrogen sulphide molecules are held to one another only by weak van der Waals forces (1 mark). Hydrogen bonds are much stronger than these weak forces, so far more heat energy is needed to separate water molecules, giving water the higher boiling point (1 mark). No mark for answers claiming that covalent bonds are broken on boiling.

6. Question 6

   4 marks

   Magnesium (2.8.2) burns in chlorine (2.8.7) to form magnesium chloride. Describe how the bond in magnesium chloride is formed.

   (4 marks)

   Marking scheme

   Each magnesium atom loses the two electrons in its outermost shell (1 mark), forming a Mg2+ ion with the stable configuration 2.8 (1 mark). Each chlorine atom gains one electron to complete its outermost shell, forming a Cl- ion, so two chlorine atoms are needed for every magnesium atom (1 mark). The oppositely charged ions are held together by strong electrostatic forces of attraction in a lattice, giving MgCl2 (1 mark).

7. Question 7

   3 marks

   Graphite is used to make the central rod in a dry cell. Account for this use in terms of the structure and bonding of graphite.

   (3 marks)

   Marking scheme

   In graphite each carbon atom is covalently bonded to only three other carbon atoms (1 mark), so one outer electron per atom is not used in bonding and is delocalised between the layers (1 mark). These delocalised electrons are free to move through the structure and carry current, so graphite conducts electricity while remaining a non-metal that is unreactive towards the cell chemicals (1 mark).

8. Question 8

   2 marks

   Explain why ice floats on liquid water.

   (2 marks)

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9. Question 9

   3 marks

   Magnesium melts at a much higher temperature than sodium. Explain this observation in terms of metallic bonding.

   (3 marks)

   Marking scheme

   Each magnesium atom releases two outer electrons into the electron sea while each sodium atom releases only one, so magnesium has more delocalised electrons (1 mark). Magnesium also forms a smaller, more highly charged Mg2+ ion compared with Na+ (1 mark). The electrostatic attraction between the ions and the electron sea is therefore stronger in magnesium and more heat energy is needed to weaken it, giving the higher melting point (1 mark).

10. Question 10

    3 marks

    Explain why common salt obtained from Lake Magadi does not conduct electricity when solid but conducts when molten.

    (3 marks)

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11. Question 11

    1 mark

    Helium gas used to fill balloons does not form bonds with other elements. This is because

    A. its atoms are already joined to one another by strong covalent bonds

    B. it has eight electrons in its outermost shell

    C. it readily loses its two electrons to other atoms

    D. its only electron shell already holds two electrons, which is the maximum that shell can hold

    (1 mark)

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12. Question 12

    3 marks

    Ammonia given off from a cattle shed dissolves in water and reacts with hydrogen ions to form ammonium ions. Describe the formation of the fourth nitrogen-to-hydrogen bond in the ammonium ion.

    (3 marks)

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13. Question 13

    1 mark

    A solution of sugar in water does not conduct electricity, while a solution of common salt in water conducts. This is because

    A. sugar has a giant covalent structure while sodium chloride has a simple molecular structure

    B. the covalent bonds in sugar are broken when it dissolves

    C. sugar dissolves as separate neutral molecules, while sodium chloride dissolves to give ions that are free to move

    D. sugar molecules are much larger than sodium and chloride ions

    (1 mark)

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14. Question 14

    1 mark

    Oxygen gas exists as O2 molecules, and an oxygen atom has the electron arrangement 2.6. The two atoms in an oxygen molecule are joined by

    A. three shared pairs of electrons

    B. one shared pair of electrons

    C. two shared pairs of electrons

    D. the transfer of two electrons from one atom to the other

    (1 mark)

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15. Question 15

    1 mark

    Table salt is harvested from Lake Magadi. When a sodium atom (2.8.1) combines with a chlorine atom (2.8.7) to form sodium chloride, what happens to the electrons?

    A. Each sodium atom shares one electron with a chlorine atom so that both attain a full outer shell

    B. Both atoms release their outer electrons into a common pool that holds them together

    C. Each sodium atom loses one electron to a chlorine atom, forming Na+ and Cl- ions

    D. Each chlorine atom loses one electron to a sodium atom, forming Cl+ and Na- ions

    (1 mark)

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16. Question 16

    4 marks

    Copper is used for overhead and household electricity cables. Explain, in terms of metallic bonding, why copper conducts electricity well and can be drawn into wires.

    (4 marks)

    Marking scheme

    Copper consists of positive ions arranged in a lattice within a sea of delocalised electrons (1 mark); these electrons come from the outermost shells of the atoms and are free to move through the whole structure (1 mark). When a potential difference is applied, the delocalised electrons drift through the metal and carry the current (1 mark). Because the attraction is between the ions and the electron sea rather than between fixed pairs of atoms, layers of ions can slide over one another without the bonding breaking, so the metal can be drawn into wire (1 mark).

17. Question 17

    6 marks

    A learner is given a white crystalline solid labelled X and told that it is either a giant ionic solid or a simple molecular solid. Describe three tests she could carry out, and state the result of each test that would show that X is a giant ionic solid.

    (6 marks)

    Marking scheme

    Test 1: heat a little of X strongly in a crucible or determine its melting point (1 mark); X does not melt easily and has a very high melting point (1 mark). Test 2: melt a sample, or dissolve it in water, and pass electricity through it using carbon electrodes and a bulb (1 mark); the molten solid or the solution conducts electricity and the bulb lights (1 mark). Test 3: shake a little of X with water and separately with an organic solvent such as paraffin (1 mark); X dissolves in water but not in the organic solvent (1 mark). Accept any three valid tests, each with its matching correct observation.

18. Question 18

    1 mark

    Ammonia used in making fertiliser contains nitrogen (atomic number 7) joined to hydrogen. A nitrogen atom forms three covalent bonds because

    A. it needs three more electrons to complete its outermost shell

    B. it must lose three electrons before it can become stable

    C. it has three shells that are not yet filled with electrons

    D. it has three electrons in its outermost shell

    (1 mark)

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19. Question 19

    1 mark

    Which one of the following compounds contains both ionic and covalent bonds?

    A. Magnesium oxide

    B. Ammonium chloride

    C. Calcium chloride

    D. Hydrogen chloride

    (1 mark)

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20. Question 20

    1 mark

    A piece of candle wax placed on a hot metal lid over a jiko melts within seconds, while common salt on the same lid stays solid. The best explanation is that

    A. wax molecules are much heavier than the ions in salt

    B. salt has a giant covalent structure while wax has a giant ionic structure

    C. only weak forces between the wax molecules have to be overcome, while the strong electrostatic forces between the ions in salt do not give way at that temperature

    D. the covalent bonds inside the wax molecules are broken by the heat while those in salt are not

    (1 mark)

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21. Question 21

    1 mark

    Graphite powder is used to lubricate the moving parts of a machine. This use depends on the fact that

    A. the layers of carbon atoms in graphite are held to one another by weak forces and can slide over each other

    B. each carbon atom in graphite is joined to four others by strong covalent bonds

    C. graphite is held together by ionic bonds that break easily

    D. graphite melts at a low temperature and forms an oily liquid

    (1 mark)

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22. Question 22

    1 mark

    An element Z has the electron arrangement 2.8.5. The formula of the compound formed when Z reacts with sodium (2.8.1) is

    A. Na3Z

    B. NaZ3

    C. NaZ

    D. Na2Z

    (1 mark)

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23. Question 23

    4 marks

    Carbon dioxide is a gas at room temperature while silicon dioxide, the main constituent of sand, melts above 1700 degrees Celsius. Account for this difference, although both compounds contain only covalent bonds.

    (4 marks)

    Marking scheme

    Carbon dioxide exists as small, separate molecules (1 mark) held to one another only by weak van der Waals forces, which need very little energy to overcome, so it is a gas (1 mark). Silicon dioxide has a giant covalent structure in which every silicon atom is bonded to oxygen atoms and every oxygen atom to silicon atoms throughout the crystal (1 mark). Melting it requires very many strong covalent bonds to be broken, which needs a great deal of heat energy (1 mark).

24. Question 24

    3 marks

    A crystal of common salt shatters into smaller pieces when struck with a hammer, while a copper coin only changes shape. Explain why the salt crystal shatters.

    (3 marks)

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25. Question 25

    1 mark

    Magnesium oxide, used to line furnaces, melts at a far higher temperature than sodium chloride. This is mainly because

    A. magnesium oxide contains covalent bonds while sodium chloride contains ionic bonds

    B. the oxide ion is much larger than the chloride ion

    C. magnesium oxide molecules are much larger than sodium chloride molecules

    D. the 2+ and 2- ions in magnesium oxide attract each other more strongly than the 1+ and 1- ions in sodium chloride

    (1 mark)

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26. Question 26

    3 marks

    Explain what is meant by a polar covalent bond, using hydrogen chloride as an example.

    (3 marks)

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27. Question 27

    1 mark

    At room temperature chlorine is a gas while iodine is a dark solid, although both exist as diatomic molecules. This difference is because

    A. iodine molecules are joined by hydrogen bonds while chlorine molecules are not

    B. iodine molecules are larger, so the van der Waals forces between them are stronger

    C. iodine molecules are held to one another by ionic bonds

    D. the covalent bond inside an iodine molecule is stronger than the one inside a chlorine molecule

    (1 mark)

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28. Question 28

    2 marks

    Explain why diamond is used in the cutting tips of rock-drilling bits.

    (2 marks)

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