OxfordAQA International GCSE Chemistry: Chemical bonds: ionic, covalent and metallic (9202) – 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 section 3.2.1, Chemical bonds: ionic, covalent and metallic, of the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. Statements a to j are all tested. There are no tiers here, so attempt every question.

Revise first with the chemical bonds study guide or the chemical bonds revision notes. See also the course hub for this qualification and the topic-by-topic checklist. Use group numbers from the periodic table wherever a question needs them.

Questions

1. Here are four substances: Br₂, CO, NaF, O₃. Identify the two compounds and give the reason for your choice. [3]

2. Calcium has atomic number 20 and fluorine has atomic number 9.

(a) Give the electron arrangement of a calcium ion in the form used for [2,8]⁺. [2] (b) Give the electron arrangement of a fluoride ion in the same form. [2] (c) Name the noble gas whose electron arrangement each ion has. [1]

3. Element X is a metal in Group 3. Element Y is a non-metal in Group 6. Predict the charge on each ion and the formula of the compound they form. [3]

4. Potassium burns in iodine vapour to form potassium iodide.

(a) Write a balanced symbol equation for the reaction. [2] (b) Explain, in terms of electrons, why potassium forms a 1+ ion and iodine forms a 1− ion. [2] (c) State the type of bonding in potassium iodide. [1]

5. Strontium is in Group 2 and chlorine is in Group 7. Draw a dot and cross diagram to show how strontium and chlorine atoms form strontium chloride. Show outer electrons only, and give the formula. [4]

6. A square layer of nine ions is taken from a sodium chloride crystal. A sodium ion sits at the centre.

(a) State which ion sits at each corner of the square, and which ion sits at the middle of each edge. [2] (b) Describe the bonding that holds the ions together in the crystal. [2]

7. (a) Draw a dot and cross diagram for a methane molecule, CH₄. [2] (b) Draw the displayed formula of water and state how many non-bonding pairs of electrons the molecule has. [2]

8. Hydrogen peroxide has the structure H–O–O–H. Oxygen is in Group 6. Draw a dot and cross diagram for one molecule, and state the number of shared pairs and non-bonding pairs it contains. [3]

9. A diagram of silicon dioxide shows each silicon atom joined by lines to four oxygen atoms and each oxygen atom joined to two silicon atoms. The lines continue off every edge of the diagram.

(a) Identify the type of structure and give two pieces of evidence from the diagram. [3] (b) Explain how the formula SiO₂ follows from the diagram, even though silicon dioxide has no separate molecules. [2]

10. Describe the structure and bonding in solid sodium. Include what you would draw and label in a diagram. [4]

11. Element Q has atomic number 19. Element R has atomic number 17.

(a) Give the electron arrangement of an atom of each element. [2] (b) Give the electron arrangement of the ion each element forms, in the form used for [2,8]⁺. [2] (c) State the type of bonding in the compound of Q and R, and give its formula. [2] (d) Element R also exists as R₂ molecules. Describe the bonding in one R₂ molecule. [1]

12. Compare the bonding in sodium metal, sodium fluoride and fluorine gas. [6]

Answers

1. CO [1] and NaF [1]. Each contains atoms of two different elements chemically combined; Br₂ and O₃ contain only one element each [1]. [3] Examiner insight: Picking the right two without a reason earns only the identification points; the reason must mention two or more elements being chemically combined.

2. (a) The atom is 2,8,8,2 and loses two electrons [1], giving [2,8,8]²⁺ [1]. (b) The atom is 2,7 and gains one electron [1], giving [2,8]⁻ [1]. (c) Calcium ion: argon; fluoride ion: neon [1]. Examiner insight: An arrangement written without the square brackets, or with the charge missing, does not match the form the question asks for and can cost a point.

3. X loses three electrons, so X³⁺ [1]. Y gains two electrons, so Y²⁻ [1]. Two X³⁺ (total +6) balance three Y²⁻ (total −6), so the formula is X₂Y₃ [1]. [3] Examiner insight: Show the charge balance; a formula with no working can still score, but a slip in it then leaves nothing to credit.

4. (a) Correct formulae, with iodine as I₂ [1]. Balanced: 2K + I₂ → 2KI [1]. (b) Potassium has one outer electron, which it loses to reach a noble gas arrangement [1]. Iodine has seven outer electrons and gains one to complete its outer shell [1]. (c) Ionic [1]. Examiner insight: Writing iodine as I in the equation is a common slip; halogens are diatomic, and an unbalanced equation loses the balancing point.

5. Strontium atom shown losing its two outer electrons (dots) [1]. Two chlorine atoms, each gaining one electron (crosses plus one dot, eight outer electrons) [1]. Ions in square brackets with charges: [Sr]²⁺ and 2 × [Cl]⁻ [1]. Formula SrCl₂ [1]. [4]

Sr ••   +  2 Cl (7 x each)
   ->  [Sr]2+   [Cl: 7 x + 1 •]-   [Cl: 7 x + 1 •]-

Examiner insight: Drawing one chlorine atom gaining two electrons, or one Cl²⁻ ion, contradicts Group 7 chemistry and loses both the ion and the formula points.

6. (a) Corners: Na⁺ [1]. Edge midpoints: Cl⁻ [1]. (b) Strong electrostatic forces of attraction between oppositely charged ions [1], acting in all directions throughout the giant lattice [1]. Examiner insight: In part (b), “ionic bonds between atoms” or “between molecules” names the wrong particles; the attraction must be between oppositely charged ions.

7. (a) Four shared pairs between C and four H atoms [1], each pair one dot and one cross, with no non-bonding pairs [1]. (b) H–O–H [1]. Two non-bonding pairs, both on the oxygen [1]. Examiner insight: Two electrons from the same atom in a shared pair, or eight electrons around a hydrogen, each make a dot and cross diagram wrong, so check every pair and every hydrogen.

8. One shared pair between each H and its O, and one shared pair between the two O atoms [1]. Two non-bonding pairs on each oxygen [1]. 3 shared pairs and 4 non-bonding pairs [1]. [3]

H-O overlaps (x2):  one • from H + one x from O
O-O overlap:        one electron from each O atom
Left on each O:     two non-bonding pairs

Check: 1 + 6 + 6 + 1 = 14 = 2 × (3 + 4). Examiner insight: Count all outer electrons before drawing; a diagram whose total does not match the atoms’ outer electrons cannot be fully correct.

9. (a) Giant covalent structure (macromolecule) [1]. Evidence: atoms joined by covalent bonds (lines) to several neighbours [1]; the network continues off every edge, so there are no separate molecules [1]. (b) Each silicon has four oxygens, but each oxygen is shared between two silicons [1], so there are half as many silicon atoms as oxygen atoms: Si : O = 1 : 2 [1]. Examiner insight: “It has strong bonds” is not evidence from the diagram; your evidence should point to something you can see, such as bonds running off the edges.

10. A giant structure of sodium atoms arranged in a regular pattern [1]. The outer electron of each atom is delocalised, free to move through the whole structure [1]. This leaves Na⁺ ions held together by strong electrostatic attraction to the delocalised electrons [1]. Diagram: a regular lattice of circles marked + with electrons (or shading) between them, labelled “delocalised electrons” [1]. [4] Examiner insight: Writing “free electrons” alone, with no idea that they move through the whole structure, or saying “free ions”, weakens the description of delocalisation.

11. (a) Q: 2,8,8,1 [1]. R: 2,8,7 [1]. (b) Q⁺: [2,8,8]⁺ [1]. R⁻: [2,8,8]⁻ [1]. (c) Ionic (Q is a Group 1 metal, R a Group 7 non-metal) [1]. Formula QR [1]. (d) The two R atoms are joined by a single covalent bond: one pair of electrons, one from each atom [1]. Examiner insight: Work from the atomic number every time; an arrangement with nine electrons in the third shell for Q shows the shell-filling rule was not applied.

12. Indicative content, one point each, up to 6:

• Sodium metal: giant structure of atoms in a regular pattern [1].
• Outer electrons are delocalised; positive ions attract the delocalised electrons [1].
• Sodium fluoride: sodium transfers one electron to fluorine, forming Na⁺ and F⁻ [1].
• Sodium fluoride is a giant lattice of ions held by strong electrostatic attraction between oppositely charged ions in all directions [1].
• Fluorine: the two atoms in each molecule are held by one shared electron pair [1].
• Fluorine is made of simple F₂ molecules; each atom reaches a noble gas arrangement [1]. [6] Examiner insight: A comparison question needs every substance covered; six points about one substance leave the comparison unanswered, so plan two points for each.

Where marks are usually lost

• Describing ionic compounds as molecules, or the ionic bond as a link between two atoms.
• Drawing ions with no brackets or no charge.
• Using the wrong number of atoms, so electrons lost do not equal electrons gained.
• Writing halogens as single atoms (I, Cl) in equations instead of I₂, Cl₂.
• Missing non-bonding pairs on O, N or halogen atoms in covalent diagrams.
• Putting a negative charge on a metal ion or a positive one on a non-metal ion.
• Saying “free ions” or “free protons” in a metal instead of delocalised electrons.
• Treating silicon dioxide as a simple molecule because its formula is small.
• Answering a comparison question about only one of the substances named.

Next steps

• Chemical bonds revision notes
• Chemical bonds study guide
• Course hub
• Course checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

Source document: the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, from OxfordAQA. These questions follow its section 3.2.1, Chemical bonds: ionic, covalent and metallic.