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IGCSE Chemistry Paper 4 (Theory/Extended)

Topic 2: Atoms, Elements and Compounds -- Mock Exam 2
75 minutes
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Question Navigation Score: 0 / 80

Question 1 -- Elements, Compounds and Mixtures
Total: 12 marks
A chemistry laboratory in Mumbai is testing a collection of substances. The technician has labelled each sample and needs to classify them correctly.
(a) [3]
Define each of the following terms:
(i) element
(ii) compound
(iii) mixture
Model Answer -- 1(a)
(i) An element is a substance that contains only one type of atom / cannot be broken down into simpler substances by chemical methods [1]
(ii) A compound is a substance formed when two or more elements are chemically combined / bonded together in a fixed ratio [1]
(iii) A mixture is two or more substances (elements or compounds) that are not chemically combined / can be separated by physical methods [1]
⚠ If you missed marks here: The word "mixed" has no place in a definition of a compound: a compound has elements CHEMICALLY COMBINED in a fixed ratio, while a mixture's substances are not combined and can be separated by PHYSICAL methods. For an element, say one TYPE of atom – "a single atom" is wrong, since a lump of copper contains billions of atoms.
(b) [4]
Classify each of the following substances as an element, compound or mixture. Give a reason for each answer.

(i) Copper wire
(ii) Sea water
(iii) Carbon dioxide gas
(iv) Bronze (an alloy of copper and tin)
Model Answer -- 1(b)
(i) Copper wire -- element; it contains only copper atoms / only one type of atom [1]
(ii) Sea water -- mixture; it contains water, dissolved salts, and other substances that are not chemically combined [1]
(iii) Carbon dioxide -- compound; it contains carbon and oxygen atoms chemically bonded together in a fixed ratio (CO2) [1]
(iv) Bronze -- mixture; it contains copper and tin atoms mixed together but not chemically bonded / can vary in composition [1]
⚠ If you missed marks here: Bronze is the trap: an alloy is a MIXTURE of a metal with other elements, not a compound, because the copper and tin are not chemically bonded and the proportions can vary. Each mark also needs its reason – a correct label with no reason, such as "sea water: mixture", does not score.
(c) [3]
A student in the laboratory has a mixture of iron filings and sulfur powder. Describe a physical method to separate the iron from the sulfur. Explain why this method works and state one observation the student would make.
Model Answer -- 1(c)
Pass a magnet over / through the mixture [1]
Iron is magnetic and is attracted to the magnet, but sulfur is not magnetic so it remains behind [1]
Observation: the grey/silver iron filings cling to the magnet and can be pulled away from the yellow sulfur powder [1]
⚠ If you missed marks here: Do not heat the mixture – that makes iron sulfide, a chemical change, which is the opposite of separating them. A magnet works because iron is magnetic and sulfur is not; for the observation, describe what you would see, such as grey iron filings clinging to the magnet while the yellow sulfur powder stays behind.
(d) [2]
When iron filings and sulfur powder are heated strongly together, they react to form the compound iron sulfide (FeS). Iron sulfide has very different properties from both iron and sulfur.

Explain why the properties of iron sulfide are different from those of iron and sulfur.
Model Answer -- 1(d)
In a compound, the atoms of iron and sulfur are chemically bonded together / a chemical reaction has occurred [1]
The arrangement of atoms is different from the original elements, so the compound has a completely new set of properties / the chemical bonds create a new substance [1]
⚠ If you missed marks here: "Because it was heated" describes the method, not the reason. The properties change because a chemical reaction has formed a NEW substance, with the iron and sulfur atoms bonded together in a new arrangement, whereas a mixture would simply keep the properties of the iron and the sulfur.
Question 2 -- Atomic Structure and Electronic Configurations
Total: 12 marks
A science teacher in London is preparing a lesson on atomic structure. She uses the periodic table to help students understand how atoms are built.
(a) [3]
Lithium has a proton number of 3 and a nucleon number of 7.

State the number of protons, neutrons and electrons in a lithium atom. Draw a labelled diagram showing the arrangement of these subatomic particles in a lithium atom.
Model Answer -- 2(a)
Protons = 3, Neutrons = 7 - 3 = 4, Electrons = 3 [1]
Nucleus in the centre containing 3 protons and 4 neutrons [1]
Electrons arranged in shells: 2 electrons in the first shell, 1 electron in the second shell (electronic configuration 2,1) [1]
3p+ 4n Shell 1 e e Shell 2 e Lithium atom (2,1)
⚠ If you missed marks here: Neutrons = 7 − 3 = 4; writing 7 confuses the nucleon number with the neutron count. In the diagram, put the protons and neutrons together in the central nucleus, and place the 3 electrons 2 in the first shell and 1 in the second – three electrons in the first shell loses the arrangement mark.
(b) [4]
Complete the following table for the atoms shown.

Atom Proton number Nucleon number Electrons Electronic configuration
Sodium (Na) 11 23 ? ?
Phosphorus (P) ? 31 15 ?
Argon (Ar) 18 ? 18 ?
Note: Argon has nucleon number 40.
Model Answer -- 2(b)
Sodium: electrons = 11, electronic configuration = 2,8,1 [1]
Phosphorus: proton number = 15, electronic configuration = 2,8,5 [1]
Argon: nucleon number = 40, electronic configuration = 2,8,8 [1]
All four missing values correct with electronic configurations using correct shell filling rules (max 2 in first shell, max 8 in second and third shells) [1]
⚠ If you missed marks here: In a neutral atom, electrons = protons = proton number, so sodium has 11 electrons (not 23) and phosphorus has proton number 15. Argon's missing entry is its NUCLEON number, 40, given in the note – 22 is its number of neutrons, which is not what the column asks for.
(c) [3]
An element X has the electronic configuration 2,8,7.

(i) Identify element X.
(ii) State the group and period of element X in the periodic table.
(iii) Explain how the electronic configuration tells you the group and period.
Model Answer -- 2(c)
(i) Element X is chlorine (Cl), proton number 17 [1]
(ii) Group VII (or Group 17), Period 3 [1]
(iii) The number of electron shells = the period number (3 shells = Period 3). The number of electrons in the outer shell = the group number (7 outer electrons = Group VII) [1]
⚠ If you missed marks here: Add 2 + 8 + 7 = 17 to find the proton number: that is chlorine, so naming nitrogen or fluorine comes from reading only part of the configuration. For (iii), keep the two rules the right way round – the number of shells (3) gives the PERIOD and the number of outer electrons (7) gives the GROUP.
(d) [2]
The noble gases (Group 0/VIII) include helium (2), neon (2,8) and argon (2,8,8).

Explain, with reference to electronic configuration, why the noble gases are very unreactive.
Model Answer -- 2(d)
Noble gases have a full/complete outer shell of electrons (stable electronic configuration / stable octet, except helium which has a stable duplet) [1]
They have no tendency to gain, lose or share electrons, so they do not form bonds / do not react with other elements [1]
⚠ If you missed marks here: The reason is a FULL outer shell, not "8 outer electrons" – helium has only 2 and is just as unreactive. The second mark needs the consequence: with a full shell the atoms have no tendency to gain, lose or share electrons, so they do not form bonds.
Question 3 -- Isotopes
Total: 12 marks
A hospital in Singapore uses different isotopes in medical imaging and treatment. A chemistry student is learning about the concept of isotopes and their applications.
(a) [2]
Define the term isotopes.
Model Answer -- 3(a)
Isotopes are atoms of the same element / with the same proton number (Z) [1]
but with different numbers of neutrons / different nucleon numbers (A) [1]
⚠ If you missed marks here: Both marks hinge on which particle changes: isotopes have the SAME proton number (so they are the same element) but DIFFERENT numbers of neutrons. "Different numbers of protons" would make them different elements, and "different numbers of electrons" describes ions, not isotopes.
(b) [2]
Silicon has three naturally occurring isotopes: silicon-28, silicon-29 and silicon-30. The proton number of silicon is 14.

Write the nuclide notation for:
(i) silicon-28
(ii) silicon-29
Model Answer -- 3(b)
(i) ²⁸⁄₁₄Si -- nucleon number 28 at top left, proton number 14 at bottom left [1]
(ii) ²⁹⁄₁₄Si -- nucleon number 29 at top left, proton number 14 at bottom left [1]
28 14 Si Silicon-28 29 14 Si Silicon-29
⚠ If you missed marks here: In nuclide notation the nucleon number (28 or 29) goes at the TOP left of the symbol and the proton number (14) at the BOTTOM left – and the bottom number is the same for every isotope of silicon. Writing them upside down, or putting the neutron number (14 or 15) on top, loses the mark.
(c) [4]
The percentage abundances of the three silicon isotopes are:

Isotope Mass number Percentage abundance
Silicon-28 28 92.2%
Silicon-29 29 4.7%
Silicon-30 30 3.1%

Calculate the relative atomic mass (Ar) of silicon. Show your working clearly and give your answer to one decimal place.
Model Answer -- 3(c)
Ar = sum of (isotope mass x percentage abundance) / 100 [1]
Ar = (28 x 92.2) + (29 x 4.7) + (30 x 3.1) / 100 [1]
Ar = (2581.6 + 136.3 + 93.0) / 100 = 2810.9 / 100 [1]
Ar = 28.1 (to 1 decimal place) [1]
⚠ If you missed marks here: Weight each mass number by its abundance; a plain average, (28 + 29 + 30) ÷ 3 = 29.0, ignores the fact that 92.2% of silicon atoms are silicon-28. Divide the total, 2810.9, by 100 and give one decimal place, 28.1 – leaving 2810.9 or rounding to 28 each cost a mark.
(d) [2]
Explain why all three isotopes of silicon have the same chemical properties.
Model Answer -- 3(d)
All three isotopes have the same number of electrons / same electronic configuration (2,8,4) [1]
Chemical properties depend on the electronic configuration / how electrons are arranged, not on the number of neutrons in the nucleus [1]
⚠ If you missed marks here: Neutrons take no part in reactions, so the extra neutrons in silicon-29 and silicon-30 make no difference to the chemistry. The marks are for saying all three have the same number of electrons, arranged 2,8,4, and that chemical properties depend on the electrons – "the same number of protons" alone does not score.
(e) [2]
Although isotopes have the same chemical properties, they can have slightly different physical properties such as density and rate of diffusion.

Suggest why isotopes may differ in their rate of diffusion.
Model Answer -- 3(e)
Different isotopes have different masses / different numbers of neutrons make them heavier or lighter [1]
Heavier isotopes move more slowly at the same temperature / have lower average speed, so they diffuse more slowly [1]
⚠ If you missed marks here: The difference comes from MASS, not electrons: the heavier isotope (more neutrons) moves more slowly at the same temperature, so it diffuses more slowly. Saying the heavier isotope diffuses faster, or bringing electrons into the answer, loses the marks.
Question 4 -- Ionic Bonding
Total: 12 marks
A materials scientist at a research institute in Cambridge is studying ionic compounds. She investigates how atoms of metals and non-metals combine to form ionic bonds.
(a) [3]
Magnesium (Mg) has the electronic configuration 2,8,2. Oxygen (O) has the electronic configuration 2,6.

Describe, in terms of electron transfer, how magnesium and oxygen atoms form ions when they react to form magnesium oxide (MgO). Include the charges on the ions formed.
Model Answer -- 4(a)
Magnesium atom loses its 2 outer shell electrons to form a Mg²+ ion (with electronic configuration 2,8) [1]
Oxygen atom gains these 2 electrons to form an O²− ion (with electronic configuration 2,8) [1]
Both ions now have a stable noble gas electronic configuration (same as neon) / full outer shell of electrons [1]
⚠ If you missed marks here: The electrons are TRANSFERRED, not shared: magnesium loses its 2 outer electrons to become Mg2+ and oxygen gains those 2 to become O2−. Losing electrons makes a POSITIVE ion, so Mg2− reverses the transfer; the third mark is for both ions ending with the noble-gas arrangement 2,8.
(b) [3]
Draw a dot-and-cross diagram to show the ionic bonding in magnesium oxide (MgO). Show the outer electron shells only, the charges on the ions, and use dots for one element and crosses for the other.
Model Answer -- 4(b)
Mg²+ ion shown with no outer electrons (empty outer shell / all electrons transferred) with 2+ charge [1]
O²− ion shown with 8 electrons in outer shell (6 shown as crosses from oxygen, 2 shown as dots from magnesium) with 2- charge [1]
Square brackets around each ion with charges outside the brackets [1]
2+ Mg (no outer electrons) ionic bond 2- O x x x • x x • x x = electron from oxygen • = electron from magnesium
⚠ If you missed marks here: Showing outer shells only, magnesium's shell is EMPTY after the transfer and oxygen's holds 8 – 6 crosses of its own plus 2 dots from magnesium. Put each ion in its own square brackets with the charge OUTSIDE at the top right; leaving out brackets or charges, or drawing the atoms overlapping as if they shared electrons, loses marks.
(c) [3]
Calcium has the electronic configuration 2,8,8,2. Chlorine has the electronic configuration 2,8,7.

Draw a dot-and-cross diagram to show the ionic bonding in calcium chloride (CaCl2). Show outer shells only.
Model Answer -- 4(c)
Ca²+ ion shown with empty outer shell and 2+ charge, in square brackets [1]
Two Cl− ions each with 8 electrons in outer shell (7 from Cl shown as crosses, 1 from Ca shown as a dot), each with 1− charge [1]
Correct ratio of one Ca²+ to two Cl− ions, showing that calcium transfers one electron to each chlorine atom [1]
- Cl x x x • x x x x 2+ Ca - Cl x x x • x x x x x = electron from Cl • = electron from Ca
⚠ If you missed marks here: Calcium has 2 electrons to give and each chlorine takes only 1, so you need TWO chloride ions – drawing one Cl receiving both electrons (a "Cl2−" ion) is the commonest error. Each chloride ion should show 8 outer electrons, 7 of its own and 1 from calcium, with a 1− charge.
(d) [3]
Magnesium oxide has a very high melting point (2852 °C). It does not conduct electricity when solid but does conduct when molten.

Explain these properties in terms of the structure and bonding in magnesium oxide.
Model Answer -- 4(d)
MgO has a giant ionic lattice structure with strong electrostatic forces of attraction between the oppositely charged Mg²+ and O²− ions in all directions. A large amount of energy is needed to overcome these strong forces, so the melting point is very high [1]
In the solid state, the ions are held in fixed positions in the lattice and cannot move, so they cannot carry charge / conduct electricity [1]
When molten, the ions are free to move throughout the liquid and can carry charge / act as mobile charge carriers, so the molten compound conducts electricity [1]
⚠ If you missed marks here: Molten MgO conducts because its IONS are free to move – "delocalised electrons" belongs to metals and scores nothing here, while in the solid the same ions are locked in the lattice. The high melting point needs strong electrostatic attraction between oppositely charged ions throughout a giant lattice; any mention of molecules or intermolecular forces loses that mark.
Question 5 -- Covalent Bonding
Total: 10 marks
Covalent compounds are found everywhere in daily life -- from the carbon dioxide we exhale to the ethene used to make plastic bags. A student in Delhi is studying how atoms share electrons to form covalent bonds.
(a) [1]
Define the term covalent bond.
Model Answer -- 5(a)
A covalent bond is a shared pair of electrons between two atoms [1]
⚠ If you missed marks here: A covalent bond is a shared PAIR of electrons between two atoms – "sharing of electrons" without the word pair, or a pair "between two ions", is not enough. Transferring electrons is ionic bonding, not covalent.
(b) [3]
Carbon has 4 outer electrons. Oxygen has 6 outer electrons.

Draw a dot-and-cross diagram for a molecule of carbon dioxide (CO2). Show the outer electron shells only. Carbon dioxide contains two carbon-oxygen double bonds.
Model Answer -- 5(b)
Each oxygen atom shares two pairs of electrons with the central carbon atom (double bond = two shared pairs) [1]
Carbon has 8 electrons around it (4 of its own + 4 shared from the two oxygens), each oxygen has 8 electrons around it (4 lone pair + 2 own bonding + 2 shared from carbon) [1]
Two lone pairs on each oxygen correctly shown, with dots and crosses used to distinguish atoms [1]
O C O x x x x x • x • • x • x x x x x x = electron from O • = electron from C
⚠ If you missed marks here: Each carbon–oxygen link is a DOUBLE bond, so draw two shared pairs (4 electrons) in each overlap – single bonds leave carbon with only 6 electrons. Then check every atom has 8: carbon gets all 8 from bonding, each oxygen keeps 2 lone pairs, and carbon itself has no lone pairs.
(c) [3]
Ethene (C2H4) contains a carbon-carbon double bond. Each carbon atom is also bonded to two hydrogen atoms.

Draw a dot-and-cross diagram for a molecule of ethene. Show the outer electron shells only.
Model Answer -- 5(c)
Carbon-carbon double bond shown correctly (two shared pairs of electrons between the two carbon atoms) [1]
Each carbon bonded to two hydrogen atoms with single covalent bonds (one shared pair each), giving each carbon 8 electrons in its outer shell [1]
Dots and crosses used correctly to distinguish electrons from different atoms; each hydrogen has 2 electrons around it (shared pair) [1]
C C • o • o H • x H • x H o x H o x • = electron from left C o = electron from right C x = electron from H
⚠ If you missed marks here: Ethene's two carbons share TWO pairs (a double bond); with a single C–C bond each carbon is left with an unpaired electron and only 7 outer electrons, and adding a third hydrogen to fix that turns the molecule into ethane, C2H6. Check: each carbon has 8 outer electrons and each hydrogen exactly 2.
(d) [3]
Carbon dioxide (CO2) is a gas at room temperature with a very low boiling point (-78 °C). However, silicon dioxide (SiO2), which also contains covalent bonds, has a very high melting point (1710 °C).

Explain why CO2 has a very low boiling point while SiO2 has a very high melting point, even though both contain covalent bonds.
Model Answer -- 5(d)
CO2 exists as simple/small individual molecules with weak intermolecular forces (forces between molecules). Only a small amount of energy is needed to overcome these weak forces, so the boiling point is very low [1]
SiO2 has a giant covalent structure where every silicon atom is bonded to four oxygen atoms in a continuous 3D network / there are no individual molecules [1]
In SiO2, many strong covalent bonds must be broken to melt it, which requires a very large amount of energy, giving it a very high melting point [1]
⚠ If you missed marks here: Boiling CO2 does NOT break its C=O covalent bonds – only the weak forces BETWEEN its molecules are overcome, so "CO2 has weak covalent bonds" loses the first mark. SiO2 has no separate molecules at all: melting it means breaking many strong covalent bonds throughout its giant network.
Question 6 -- Giant Covalent Structures
Total: 12 marks
A materials engineer in Bengaluru is selecting materials for different industrial applications. She is comparing the structures and properties of diamond, graphite, and silicon dioxide.
(a) [4]
Diamond is an allotrope of carbon. It is the hardest naturally occurring substance known.

(i) Describe the structure of diamond.
(ii) Use the structure of diamond to explain why it is very hard and has a very high melting point.
Model Answer -- 6(a)
(i) Diamond has a giant covalent structure / giant molecular structure / macromolecular structure [1]
Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement, forming a rigid 3D network [1]
(ii) Diamond is very hard because the rigid 3D network of strong covalent bonds extends in all directions, so there are no layers that can slide [1]
It has a very high melting point because many strong covalent bonds must be broken to melt it, which requires a very large amount of energy [1]
Diamond Structure C C C C C Each C bonded to 4 others (tetrahedral)
⚠ If you missed marks here: Each carbon is bonded to FOUR others in a rigid tetrahedral network (three is graphite). Hardness and the high melting point both come from strong covalent bonds running in every direction with no layers to slide; "strong intermolecular forces" is wrong, because diamond is one giant structure, not separate molecules.
(b) [4]
Graphite is another allotrope of carbon. It is used as a lubricant and in pencil leads. Unlike diamond, graphite is soft and slippery, and it conducts electricity.

(i) Describe the structure of graphite.
(ii) Explain why graphite is soft and slippery.
(iii) Explain why graphite can conduct electricity.
Model Answer -- 6(b)
(i) Graphite has a giant covalent layered structure. Each carbon atom is bonded to three other carbon atoms in flat hexagonal layers [1]
The layers are held together by weak intermolecular forces (weak van der Waals forces between the layers) [1]
(ii) Graphite is soft and slippery because the weak forces between layers allow the layers to slide over each other easily [1]
(iii) Each carbon atom uses only 3 of its 4 outer electrons for bonding, so each carbon has one delocalised / free electron. These delocalised electrons can move along the layers and carry charge, allowing graphite to conduct electricity [1]
Graphite Structure Weak forces between layers Layers slide over each other; delocalised electrons move along layers
⚠ If you missed marks here: Graphite is slippery because the forces BETWEEN its layers are weak, so the layers slide; the covalent bonds WITHIN each layer are strong and do not break. It conducts because each carbon uses only 3 of its 4 outer electrons in bonds, leaving one delocalised electron that moves along the layers – not because the layers slide, and not because of ions.
(c) [4]
Silicon dioxide (SiO2) is used in optical fibres and in the manufacture of glass. It has a melting point of 1710 °C and does not conduct electricity.

(i) Describe the structure of silicon dioxide.
(ii) Explain why silicon dioxide has a very high melting point.
(iii) Explain why silicon dioxide does not conduct electricity.
Model Answer -- 6(c)
(i) Silicon dioxide has a giant covalent structure similar to diamond. Each silicon atom is covalently bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a continuous 3D network [1]
(ii) It has a very high melting point because there are many strong covalent bonds throughout the giant structure, and a very large amount of energy is needed to break these bonds [1]
(iii) All electrons are involved in covalent bonding / there are no free or delocalised electrons to carry charge [1]
There are no ions present, so there are no mobile charge carriers at all [1]
Silicon Dioxide Structure Si O O O O Si Si Si Si Each Si bonded to 4 O; each O bonded to 2 Si
⚠ If you missed marks here: Part (iii) is worth TWO marks, so rule out BOTH possible charge carriers: no delocalised electrons (all are used in covalent bonds) AND no ions. In (i), each silicon bonds to four oxygens and each oxygen to two silicons in a giant 3D network – treating SiO2 as small molecules like CO2 loses the structure mark.
Question 7 -- Metallic Bonding
Total: 10 marks
India is one of the world's largest producers of steel. An engineer at the Tata Steel plant in Jamshedpur is explaining the properties of metals to a group of visiting students.
(a) [3]
Describe metallic bonding. Include in your answer a description of the structure and the role of electrons.
Model Answer -- 7(a)
In a metal, the atoms lose their outer shell electrons to form a lattice / regular arrangement of positive metal ions (cations) [1]
The outer electrons become delocalised / free to move throughout the whole structure (they are no longer associated with any particular metal atom) [1]
Metallic bonding is the strong electrostatic attraction between the positive metal ions and the sea / cloud of delocalised electrons [1]
Metallic Bonding M+ M+ M+ M+ M+ e e e e e e e e Sea of delocalised electrons
⚠ If you missed marks here: Describe all three parts: a regular lattice of POSITIVE ions, outer electrons that are delocalised through the whole structure, and the strong electrostatic attraction between the two. Answers that put negative ions in the metal, or say the atoms "share" electrons in pairs, describe ionic or covalent bonding instead.
(b) [2]
Copper is widely used for electrical wiring.

Use your knowledge of metallic bonding to explain why metals such as copper are good conductors of electricity.
Model Answer -- 7(b)
Metals contain delocalised / free electrons that are not attached to any particular atom [1]
When a voltage / potential difference is applied, these delocalised electrons can move through the metal structure towards the positive terminal, carrying the electric charge / current [1]
⚠ If you missed marks here: "Copper has free ions" is the commonest wrong answer: the positive ions are fixed in the lattice, and it is the delocalised ELECTRONS that move through the metal when a voltage is applied. The second mark needs that movement of electrons carrying the charge, not just the fact that they exist.
(c) [2]
Metals are malleable, which means they can be hammered into different shapes without breaking. This is why steel can be pressed into car body panels at the factory.

Use your knowledge of metallic bonding to explain why metals are malleable.
Model Answer -- 7(c)
When a force is applied, the layers of positive metal ions can slide over each other into new positions [1]
The delocalised electrons can adjust / re-form the metallic bonds in the new positions, so the structure does not break / the bonding is maintained [1]
⚠ If you missed marks here: Metallic bonding is strong, so "weak bonds let it bend" is wrong. Under a force the LAYERS of positive ions slide over one another, and because the delocalised electrons attract the ions wherever they are, the bonding holds in the new positions and the metal changes shape without breaking.
(d) [3]
Both metals and ionic compounds contain positive ions arranged in a lattice. However, metals can conduct electricity in the solid state, while ionic compounds cannot.

State three differences between metallic bonding and ionic bonding.
Model Answer -- 7(d)
In metallic bonding, electrons are delocalised / shared across all atoms; in ionic bonding, electrons are transferred from one atom to another [1]
Metallic bonding involves attraction between positive ions and delocalised electrons; ionic bonding involves attraction between positive cations and negative anions [1]
Metals conduct electricity in the solid state (due to mobile delocalised electrons); ionic compounds only conduct when molten or dissolved (when ions become mobile) [1]
⚠ If you missed marks here: Each difference must compare the two directly: delocalised electrons against electrons transferred, positive ions with a sea of electrons against cations with anions, and conduction as a solid against conduction only when molten or dissolved. "Ionic compounds cannot conduct electricity" is wrong – they do once their ions are free to move.

Exam Score Summary

0
80
0%
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A* : 56+
A : 48-55
B : 40-47
C : 32-39
Below C : <32
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IGCSE Chemistry 0620 -- Paper 4 Theory (Extended) -- Topic 2: Atoms, Elements and Compounds -- Mock Exam 2

Core + Supplement | 80 marks | 75 minutes

For exam practice only. Not affiliated with Cambridge Assessment International Education.