AQA GCSE Chemistry 8462: Covalent bonding and metallic bonding – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sections 4.2.1.4 Covalent bonding and 4.2.1.5 Metallic bonding of the AQA GCSE Chemistry (8462) specification, for teaching from September 2016 with exams from June 2018 (version 1.1). The content is examined on Paper 1. Nothing in these sections is Higher tier only, so every question is for both tiers. Questions 11 and 12 are extended responses.

Learn the content first in the study guide and the revision notes. For ionic bonding, use the separate ionic bonding practice questions. The course hub is AQA GCSE Chemistry and the printable checklist lists every statement.

Questions

1. Here are six formulas: CH₄, SiO₂, NaCl, NH₃, Cu, H₂O. Give the three that are substances made of small molecules. [3]

2. Describe what a covalent bond is, and explain why it is a strong bond. [3]

3. This question is about a dot and cross diagram of a hydrogen chloride molecule, HCl.

(a) State the number of electrons shared between the two atoms. [1] (b) State the number of non-shared pairs of electrons on the chlorine atom. [1] (c) State the total number of electrons in the outer shell of the chlorine atom in the molecule. [1]

4. Oxygen gas is made of O₂ molecules.

(a) State the number of electrons shared between the two oxygen atoms. [1] (b) Explain, in terms of electrons, why the two oxygen atoms are joined by a double bond. [3]

5. Diagram X is a displayed formula:

    H   H   H
    |   |   |
H - C - C - C - H
    |   |   |
    H   H   H

(a) Give the molecular formula of X. [1] (b) State the number of covalent bonds in one molecule of X. [1] (c) Calculate the total number of electrons shared in one molecule of X. [1]

A ball and stick model of molecule Y shows two red balls joined to each other by one stick, with one white ball joined to each red ball. Red = oxygen, white = hydrogen.

(d) Give the molecular formula of Y and explain why it should not be written as HO. [2]

6. Methane can be shown as a dot and cross diagram, a 2D displayed formula, a ball and stick model and a 3D space-filling model.

(a) Give one limitation of the 2D displayed formula. [1] (b) Give one limitation of the ball and stick model. [1] (c) Give one thing the dot and cross diagram shows that the displayed formula does not. [1] (d) Give one limitation of the 3D space-filling model. [1]

7. Silicon carbide is a giant covalent structure. Each silicon atom is covalently bonded to four carbon atoms, and each carbon atom is covalently bonded to four silicon atoms.

(a) Deduce the formula of silicon carbide. Explain your answer. [2] (b) Silicon dioxide and carbon dioxide have formulas of the same pattern, SiO₂ and CO₂. Explain why you cannot tell from the formula alone which one is a giant covalent structure. [2] (c) State the number of covalent bonds formed by each carbon atom in diamond. [1]

8. Poly(ethene) is a polymer made from repeating units of formula C₂H₄.

(a) Draw the repeating unit of poly(ethene), using a line to represent each single covalent bond. [2] (b) State what n represents in the polymer formula. [1] (c) One poly(ethene) chain has n = 5000. Calculate the number of carbon atoms and the number of hydrogen atoms in this chain. [2]

9. This question is about metallic bonding.

(a) Describe the structure of a solid metal. [2] (b) Explain why metallic bonds are strong. [2] (c) State how many delocalised electrons each atom provides in sodium (Group 1) and in magnesium (Group 2). [2]

10. Five diagrams are described below.

• A: rows of circles marked +, in a regular pattern, with e⁻ symbols scattered between them.
• B: many separate units, each one N atom joined to three H atoms, with space between the units.
• C: a network of atoms, each joined to four others, with bonds running off every edge of the diagram.
• D: a C–C unit with two H atoms on each C, drawn in brackets with n after the bracket.
• E: alternating + and − ions in a regular lattice.

(a) For each of A, B, C and D, state whether it shows a metallic giant structure, small molecules, a giant covalent structure or a polymer. [4] (b) Give the feature of diagram C that shows it is a giant structure. [1]

11. Methane (CH₄) and diamond (C) both contain carbon atoms that form covalent bonds. Compare the bonding and structure of methane and diamond. [6]

12. Chlorine exists as Cl₂ molecules. Copper is a metal. Compare the bonding in a chlorine molecule with the bonding in solid copper. [6]

Answers

1. CH₄ [1]; NH₃ [1]; H₂O [1]. (SiO₂ is giant covalent, NaCl is ionic, Cu is metallic.) [3] Examiner insight: Extra wrong formulas usually cancel correct ones, so give exactly three.

2. A shared pair of electrons [1] between two (non-metal) atoms [1]. It is strong because there is strong electrostatic attraction between the shared pair and the nuclei of both atoms [1]. [3] Examiner insight: “Sharing electrons” alone is not enough for the first mark: the word pair is the creditworthy point.

3. (a) 2 electrons (one shared pair) [1] (b) 3 non-shared pairs [1] (c) 8 [1] [3] Examiner insight: Answering “1” to (a) confuses one pair with one electron and scores zero.

4. (a) 4 electrons (two shared pairs) [1] (b) Each oxygen atom has 6 outer electrons [1]; each needs 2 more to fill its outer shell [1]; so the atoms share two pairs, giving each oxygen 8 outer electrons [1]. [4] Examiner insight: The explanation needs the link from 6 electrons to “needs 2” to “two pairs shared”; stating “it has a double bond” repeats the question and earns nothing.

5. (a) C₃H₈ [1] (b) 2 C–C + 8 C–H = 10 bonds [1] (c) 10 × 2 = 20 electrons [1] (d) H₂O₂ [1]; a molecular formula gives the actual number of each atom in one molecule, which is 2 H and 2 O, not a simplified ratio [1]. [5] Examiner insight: In (c), allow error carried forward from an incorrect bond count in (b), provided you multiply by 2.

6. (a) It does not show the 3D shape of the molecule / it does not show the electrons [1] (b) Any one: bonds are not physical sticks; atoms are drawn too far apart; atoms not to scale; no electrons shown [1] (c) Which atom each bonding electron came from / that each bond is a shared pair of electrons [1] (d) It is hard to see the bonds, or how many bonds there are [1] [4] Examiner insight: A limitation must fit the named model; “it is not 3D” for the ball and stick model scores zero because that model is 3D.

7. (a) SiC [1]. Every Si is bonded to 4 C and every C is bonded to 4 Si, so the ratio of Si to C atoms is 1 : 1 [1]. (b) Both formulas show 1 atom of one element to 2 of the other [1]; for a giant structure the formula shows only the ratio of atoms, not the number in a molecule, so the formula does not show the structure [1]. (c) 4 [1] [5] Examiner insight: In (a) the formula with no explanation earns only the first mark; the 1 : 1 ratio must be justified from the bonding.

8. (a) One C–C single bond with two H atoms on each C, shown with single lines [1]; square brackets around the unit with a bond line passing through each bracket and n written after it [1].

   [  H   H  ]
   [  |   |  ]
 --[--C---C--]--
   [  |   |  ]
   [  H   H  ] n

(b) A large number: the number of repeating units in the chain [1] (c) Carbon: 2 × 5000 = 10 000 [1]; hydrogen: 4 × 5000 = 20 000 [1] [5] Examiner insight: The bracket mark needs the bond lines to go through the brackets; brackets drawn around the unit with no extension bonds usually lose that mark.

9. (a) A giant structure of atoms arranged in a regular pattern [1]; the outer-shell electrons are delocalised and free to move through the whole structure [1]. (b) There is strong electrostatic attraction between the positive metal ions and the delocalised electrons [1]; these electrons are shared throughout the structure, so the attraction acts on every ion, in all directions [1]. (c) Sodium: 1 [1]; magnesium: 2 [1] [6] Examiner insight: “Free electrons” or “sea of electrons” without the idea that they are outer-shell electrons moving through the whole structure usually does not score the delocalised mark.

10. (a) A: metallic giant structure [1]; B: small molecules (ammonia) [1]; C: giant covalent structure [1]; D: polymer [1] (b) The bonds run off every edge, showing the network continues in all directions [1] [5] Examiner insight: E is ionic and is not asked about; classifying it earns nothing.

11. Indicative content, one mark per point, up to 6:

• In both, each carbon atom has 4 outer electrons and forms 4 covalent bonds [1].
• Each covalent bond is a shared pair of electrons, so each carbon has 8 outer electrons [1].
• In methane, each carbon bonds to 4 hydrogen atoms [1].
• Methane is a small molecule with a fixed number of atoms, CH₄ [1].
• In diamond, each carbon bonds to 4 other carbon atoms [1].
• Diamond is a giant covalent structure: the network continues in all directions with a huge number of atoms, so its formula is just C [1]. [6] Examiner insight: An answer describing only one substance is capped, because “compare” needs points about both.

12. Indicative content, one mark per point, up to 6:

• Chlorine: each Cl atom has 7 outer electrons and needs 1 more [1].
• The two atoms share one pair of electrons, a single covalent bond [1].
• The shared pair is held between those two atoms only; each Cl has 3 non-shared pairs and 8 outer electrons [1].
• Copper: a giant structure of atoms in a regular pattern [1].
• The outer-shell electrons are delocalised, free to move through the whole structure [1].
• Strong electrostatic attraction between the positive ions and the delocalised electrons forms strong metallic bonds [1]. [6] Examiner insight: The key difference is localised (between two atoms) versus delocalised (through the whole structure); “covalent shares, metallic does not” is wrong, as metallic bonding also shares electrons.

Where marks are usually lost

• Confusing electrons with pairs: a single bond is 2 shared electrons.
• Dot and cross diagrams with a shared pair shown as two dots, or placed outside the overlap.
• Leaving off non-shared pairs on N, O or Cl, so the outer shell totals fewer than 8.
• Cancelling a molecular formula (H₂O₂ to HO, N₂H₄ to NH₂).
• Treating SiO₂ as a small molecule because its formula resembles CO₂.
• Limitations that do not match the named model, or vague ones such as “it is just a model”.
• Polymer repeating units with no bond lines through the brackets, or no n.
• Metallic bonding answers that miss “regular pattern”, “delocalised” or “whole structure”.

Next steps

• Recap with the revision notes.
• Re-read anything you got wrong in the study guide.
• Revise ionic bonding with its study guide.
• Use the course hub and printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

AQA GCSE Chemistry (8462) specification, for teaching from September 2016, GCSE exams June 2018 onwards, version 1.1, published by AQA – sections 4.2.1.4 Covalent bonding and 4.2.1.5 Metallic bonding.