Ionic, covalent & metallic bonding – GCSE Chemistry exam questions with mark scheme

1Grade 1–33 marks

Give the type of bonding in each substance. Choose from: ionic, covalent, metallic.

(a) sodium chloride [1]

(b) methane, $\text{CH}_4$ [1]

(a) ionic(1)
(b) covalent(1)
(c) metallic(1)
Answer: (a) ionic (b) covalent (c) metallic
Examiner tip: Metal + non-metal → ionic; non-metals only → covalent; metal element → metallic.

2Grade 4–55 marks

Magnesium reacts with oxygen to form magnesium oxide, an ionic compound.

(a) Describe what happens to the electrons when magnesium atoms react with oxygen atoms. Give the charges on the ions formed. [4]

(b) Aluminium ions are $\text{Al}^{3+}$ and oxide ions are $\text{O}^{2-}$. Give the formula of aluminium oxide. [1]

(a) each magnesium atom loses two (outer) electrons(1)
(a) each oxygen atom gains two electrons allow two electrons are transferred from magnesium to oxygen for both of the first two marks reject any reference to sharing electrons (max 2 for (a))(1)
(a) magnesium ion: $\text{Mg}^{2+}$ allow 2+ / positive two(1)
(a) oxide ion: $\text{O}^{2-}$ allow 2− / negative two ignore references to full outer shells / noble gas structure(1)
(b) $\text{Al}_2\text{O}_3$ allow $\text{Al}_2\text{O}_3$ written with charges shown(1)
Answer: (a) Mg loses 2 e⁻ to O, giving Mg²⁺ and O²⁻ (b) Al₂O₃
Examiner tip: Say electrons are transferred — any mention of “sharing” electrons in ionic bonding loses marks.

3Grade 1–3Foundation5 marks

The figure shows a dot and cross diagram for a molecule of ammonia, $\text{NH}_3$.

Only the outer shell electrons are shown.

(a) What type of bond holds the atoms together in an ammonia molecule? [1]

(b) Give one reason why you would expect nitrogen and hydrogen to form this type of bond. [1]

(d) How many pairs of electrons on the nitrogen atom are not used in bonding? [1]

(e) How many electrons are in the outer shell of the nitrogen atom in the molecule? [1]

(a) covalent allow single covalent reject ionic / metallic(1)
(b) nitrogen and hydrogen are both non-metals allow both atoms need to gain electrons (to get a full outer shell) ignore 'they share electrons' (this describes the bond, not a reason) ignore 'they are gases'(1)
(c) 3 / three(1)
(d) 1 / one(1)
(e) 8 / eight allow 'full outer shell (of 8)'(1)
Answer: (a) covalent; (b) both are non-metals; (c) 3; (d) 1; (e) 8
Examiner tip: In (e) students often count only the crosses (5): the shared electrons from hydrogen are also in nitrogen's outer shell.

4Grade 4–5Foundation5 marks

The table gives the group number of four elements.

Element	Group	Charge on ion
lithium	1
calcium	2
sulfur	6
bromine	7

(a) Complete the table to show the charge on the ion each element forms. [2]

(b) A sulfur atom has the electronic structure 2,8,6.

Give the electronic structure of a sulfide ion. [1]

(i) lithium sulfide [1]

(ii) calcium bromide. [1]

(a) any two correct from: lithium 1+, calcium 2+, sulfur 2−, bromine 1− allow +1, +2, −2, −1 / + for 1+ and − for 1−(1)
(a) all four correct(1)
(b) 2,8,8 allow 2.8.8 / [2,8,8]²⁻ allow correctly drawn diagram(1)
(c)(i) $\text{Li}_2\text{S}$ reject LI2S / Li2s / $\text{Li}^2\text{S}$(1)
(c)(ii) $\text{CaBr}_2$ reject CaBr / $\text{CaBr}^2$ / CaBR2(1)
Answer: (a) Li 1+, Ca 2+, S 2−, Br 1−; (b) 2,8,8; (c)(i) $\text{Li}_2\text{S}$ (ii) $\text{CaBr}_2$
Examiner tip: Formulae lose marks for superscript or lower-case errors such as CaBr² or Li2s: the small number goes below the line after the element it counts.

5Grade 4–56 marks

The figure shows part of a layer of the ions in calcium chloride.

(a) Use the figure to work out the formula of calcium chloride.

Show how you worked out your answer. [2]

(b) Show that your formula gives a compound with no overall charge. [1]

(d) Give one limitation of using the figure to represent the structure of calcium chloride. [1]

(a) correct count from the figure: 6 calcium ions and 12 chloride ions allow ratio 1 : 2 / 'twice as many chloride ions' / any correct counting method(1)
(a) $\text{CaCl}_2$ allow $\text{Ca}^{2+}(\text{Cl}^-)_2$ (correct formula with no working scores 1 mark)(1)
(b) (+2) + 2 × (−1) = 0 allow one 2+ charge is balanced by two 1− charges(1)
(c) (strong) electrostatic forces (of attraction) reject intermolecular forces / covalent bonds / attraction between molecules or atoms (0 marks for (c))(1)
(c) between oppositely charged ions / between Ca²⁺ and Cl⁻ ions allow acting in all directions ignore 'ionic bonds' unqualified(1)
(d) any one from: it is 2D / only one layer, but the lattice is 3D / it only shows part of the structure (a giant lattice extends further) / ions are not drawn to scale / does not show the forces (or bonds) between ions / gaps between ions are exaggerated ignore 'not shown in colour'(1)
Answer: (a) 6 : 12 = 1 : 2, so $\text{CaCl}_2$; (b) +2 + 2(−1) = 0; (c) strong electrostatic attraction between oppositely charged ions, in all directions; (d) e.g. 2D but the lattice is 3D
Examiner tip: In (c) any mention of molecules or intermolecular forces scores zero: ionic compounds are giant lattices of ions held by electrostatic attraction.

6Grade 6–76 marks

The figure represents the structure of lithium metal.

(a) Name the particles labelled X and Y. [2]

(b) Describe the bonding in lithium metal. [3]

Suggest one way a diagram of calcium drawn in the same way would be different. Give a reason for your answer. [1]

(a) X: (positive) lithium ion / metal ion / Li⁺ reject atom / nucleus / proton / positive charge alone(1)
(a) Y: (delocalised) electron allow free electron / sea of electrons reject negative ion(1)
(b) the outer electrons are delocalised / free to move through the whole structure allow each atom loses its outer electron into a 'sea' of electrons(1)
(b) (strong) electrostatic attraction allow metallic bond for this mark only if 'attraction' is also described(1)
(b) between the positive (metal) ions and the delocalised electrons reject attraction between oppositely charged ions / ionic bonding / sharing pairs of electrons between two atoms(1)
(c) the ions would have a 2+ charge and there would be two delocalised electrons per ion / twice as many electrons because calcium atoms have 2 outer electrons allow either difference with the reason(1)
Answer: (a) X = positive (lithium) ion, Y = delocalised electron; (b) giant regular structure; outer electrons delocalised; strong electrostatic attraction between positive ions and delocalised electrons; (c) ions 2+ / two delocalised electrons per ion because Ca has 2 outer electrons
Examiner tip: Do not call metallic bonding 'attraction between oppositely charged ions': that is ionic bonding. Say positive ions and delocalised electrons.

7Grade 8–9Higher5 marks

A student drew this dot and cross diagram for a nitrogen molecule, $\text{N}_2$.

Nitrogen is in Group 5 of the periodic table.

(a) The student's diagram is not correct.

Explain why. [2]

(b) Describe the correct dot and cross diagram for a nitrogen molecule. [2]

How many electrons are shared between the two atoms in an oxygen molecule, $\text{O}_2$? [1]

(a) the diagram shows each nitrogen atom with 7 (outer) electrons of its own / 7 dots and 7 crosses allow the diagram shows only one shared pair / a single bond(1)
(a) but a nitrogen atom only has 5 outer electrons (Group 5) allow but nitrogen needs to share three pairs / form a triple bond (to gain 3 electrons) allow 14 outer electrons shown in total instead of 10 for 2 marks; 'too many electrons shown' with no numbers scores 1 mark only(1)
(b) three shared pairs of electrons (between the atoms) / a triple (covalent) bond allow six electrons shared(1)
(b) one non-bonding pair (lone pair) on each nitrogen atom allow each atom has 8 electrons in its outer shell (with 3 shared pairs)(1)
(c) 4 / four allow two (shared) pairs / a double bond reject 2(1)
Answer: (a) each N is shown with 7 of its own outer electrons, but N has only 5; (b) three shared pairs (triple bond) and one non-bonding pair on each N; (c) 4
Examiner tip: Check a dot and cross diagram by counting each atom's own symbols: they must equal its group number before you check for 8 in each outer shell.

8Grade 6–75 marks

Figure 1 shows a ball and stick model of a molecule of hydrazine.

Figure 2 shows the repeat unit of the polymer poly(chloroethene).

(a) Give the molecular formula of hydrazine. [1]

(b) Give one limitation of the ball and stick model in Figure 1. [1]

(d) One molecule of poly(chloroethene) contains 1500 repeat units.

Give the molecular formula of this molecule. Ignore the atoms at the ends of the chain. [2]

(a) $\text{N}_2\text{H}_4$ allow $\text{H}_4\text{N}_2$ reject NH₂ (empirical formula)(1)
(b) any one from: atoms are not to scale / bonds are not really sticks (atoms are much closer) / does not show which atom the electrons come from / does not show the electrons (or non-bonding pairs) / it is a fixed model, atoms and bonds vibrate allow it is drawn in 2D so does not show the 3D shape of the molecule ignore 'not in colour'(1)
(c) a (single) covalent bond allow a shared pair of electrons reject 'a bond' unqualified / one electron(1)
(d) repeat unit is $\text{C}_2\text{H}_3\text{Cl}$ allow evidence of ×1500 applied to any one element correctly(1)
(d) $\text{C}_{3000}\text{H}_{4500}\text{Cl}_{1500}$ allow $(\text{C}_2\text{H}_3\text{Cl})_{1500}$ allow elements in any order(1)
Answer: (a) $\text{N}_2\text{H}_4$; (b) e.g. atoms not to scale / does not show electrons; (c) a single covalent bond (shared pair); (d) $\text{C}_{3000}\text{H}_{4500}\text{Cl}_{1500}$
Examiner tip: In (d) count every atom inside the brackets before multiplying by the number of repeat units: the bonds that cross the brackets join units, they do not add atoms.

9Grade 8–9Higher6 marks

Rubidium (Rb) is in Group 1 of the periodic table. Selenium (Se) is in Group 6.

Rubidium reacts with selenium to form an ionic compound, rubidium selenide.

(a) Explain how rubidium selenide is formed when rubidium reacts with selenium.

Answer in terms of electrons and include the formula of rubidium selenide. [5]

(b) In a dot and cross diagram of rubidium selenide, how many electrons would be shown in the outer shell of the selenide ion? [1]

(a) (each) rubidium atom loses one electron allow outer electron(1)
(a) (each) selenium atom gains two electrons(1)
(a) so two rubidium atoms transfer one electron each to one selenium atom allow two rubidium atoms are needed for each selenium atom(1)
(a) forming Rb⁺ and Se²⁻ ions (with a noble gas / full outer shell structure) allow 1+ and 2− ions(1)
(a) $\text{Rb}_2\text{Se}$ reject RbSe₂ / RbSe / Rb²Se reject any reference to sharing electrons or covalent bonds: max 3 for (a)(1)
(b) 8 / eight(1)
Answer: (a) each Rb atom loses 1 electron, each Se atom gains 2, so 2 Rb atoms per Se atom; ions Rb⁺ and Se²⁻ with noble gas structures; $\text{Rb}_2\text{Se}$; (b) 8
Examiner tip: Unfamiliar elements: work from the group number. Group 1 gives 1+, Group 6 gives 2−, then balance the charges to get the formula.

10Grade 6–76 marks

Calcium, fluorine and calcium fluoride all contain strong chemical bonds.

Calcium is a metal in Group 2.
Fluorine is a non-metal in Group 7 and exists as $\text{F}_2$ molecules.
Calcium fluoride, $\text{CaF}_2$, is formed when calcium reacts with fluorine.

Compare the type of bonding in calcium, fluorine and calcium fluoride.

Answer in terms of electrons and the forces between particles. [6]

Calcium: metallic bonding(1)
Calcium: giant structure of (regularly arranged) positive ions / Ca²⁺ ions(1)
Calcium: outer electrons are delocalised (two per atom)(1)
Calcium: strong electrostatic attraction between positive ions and delocalised electrons(1)
Fluorine: covalent bond(s) between the two atoms(1)
Fluorine: each atom shares one electron, forming one shared pair / single bond(1)
Fluorine: so each F atom has 8 outer electrons / a noble gas structure(1)
Fluorine: the covalent bond within each F₂ molecule is strong, but the forces between F₂ molecules (intermolecular forces) are weak(1)
Calcium fluoride: ionic bonding(1)
Calcium fluoride: each calcium atom loses two electrons to form Ca²⁺(1)
Calcium fluoride: each fluorine atom gains one electron to form F⁻ (so two F per Ca)(1)
Calcium fluoride: giant lattice held by strong electrostatic attraction between oppositely charged ions, acting in all directions(1)
Comparison: electrons delocalised in calcium, shared in fluorine, transferred in calcium fluoride(1)

Level	Marks	What it looks like
Level 3	5–6	Identifies the bonding in all three substances correctly and gives a clear, linked description of what the electrons do (delocalised, shared, transferred) and of the electrostatic attraction in calcium and calcium fluoride. Comparison is coherent.
Level 2	3–4	Identifies the bonding correctly in at least two substances, with some correct description of electron behaviour or forces for each, but with gaps or limited comparison.
Level 1	1–2	Identifies at least one type of bonding correctly, or makes simple relevant statements about electrons or forces. Links are weak or missing.
No relevant content	0	Nothing worthy of credit.

Answer: Calcium: metallic – positive ions in a giant structure attracted to delocalised electrons. Fluorine: covalent – one shared pair between two F atoms. Calcium fluoride: ionic – Ca loses 2 electrons, each F gains 1, Ca²⁺ and F⁻ held by strong electrostatic forces in a giant lattice.
Examiner tip: Top-band answers name all three bond types and describe what the electrons do in each; saying 'calcium fluoride shares electrons' or 'fluorine forms F⁻ ions in F₂' caps the level.

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