IGCSE Chemistry Paper 4 (Theory / Extended)

Topic 2: Atoms, Elements and Compounds -- Mock Exam 1

Duration1 hour 15 minutes

Total Marks80

Questions7

Time Remaining75:00

Syllabus0620

Instructions

Answer all questions in the spaces provided.
Show all working for calculations.
Use appropriate scientific terminology.
Your answers will be automatically graded when you submit.

Question Navigation

Question 1 -- Elements, Compounds and Mixtures / Atomic Structure

Total: 12 marks

A chemistry teacher in Leeds shows her class five substances: iron filings, sodium chloride, air, distilled water and sulfur powder.

(a) [3]

Classify each of the following substances as an element, a compound or a mixture.

(i) Iron filings
(ii) Sodium chloride
(iii) Air

Model Answer -- 1(a)

Iron filings: element [1]

Sodium chloride: compound [1]

Air: mixture [1]

⚠ If you missed marks here: Air is a MIXTURE: its nitrogen, oxygen and other gases are not chemically joined and can be separated, so calling it a compound because it "contains different elements" is the classic slip. Sodium chloride is the opposite case – its sodium and chlorine are chemically combined in a fixed ratio, so it is a compound, not a mixture.

1 mark -- iron element 1 mark -- sodium chloride compound 1 mark -- air mixture

(b) [3]

(i) State the difference between a compound and a mixture. [2]

(ii) State one way in which an element is different from a compound. [1]

Model Answer -- 1(b)

A compound is formed by a chemical reaction / has a fixed composition, whereas a mixture is not chemically combined / has no fixed composition [1]

The components of a compound cannot be separated by physical methods, whereas the components of a mixture can be separated by physical methods [1]

An element contains only one type of atom, whereas a compound contains two or more different types of atoms chemically combined [1]

⚠ If you missed marks here: "A compound contains different elements" does not separate it from a mixture – air contains different elements too. The key words are CHEMICALLY COMBINED in a FIXED ratio (compound) against not combined and separable by physical methods (mixture); for (ii), say an element has only one TYPE of atom, not that it is "one atom".

1 mark -- compound chemical reaction fixed composition mixture not chemically combined 1 mark -- compound cannot separated physical methods mixture can separated 1 mark -- element one type atom compound two more different atoms chemically combined

Complete the table to show the relative charge and relative mass of each sub-atomic particle.

Particle	Relative charge	Relative mass
Proton	.......	1
Neutron	0	.......
Electron	.......	.......

Model Answer -- 1(c)

Proton relative charge: +1 [1]

Neutron relative mass: 1 [1]

Electron relative charge: −1 AND relative mass: 1/1836 (or negligible / very small) [1]

⚠ If you missed marks here: The electron's mark needs BOTH of its entries: charge −1 and a mass of about 1/1836 (or "negligible") – writing 0 for its mass, or copying the proton's 1, loses it. Always give the sign on a charge: "1" for the proton is not the same as +1.

1 mark -- proton charge positive one 1 mark -- neutron mass one 1 mark -- electron charge negative one mass negligible

(d) [3]

A sodium atom has a proton number (atomic number) of 11 and a nucleon number (mass number) of 23.

(i) State the number of protons, neutrons and electrons in a sodium atom. [2]

(ii) Define the term proton number. [1]

Model Answer -- 1(d)

Protons = 11, Electrons = 11 [1]

Neutrons = 23 − 11 = 12 [1]

Proton number is the number of protons in the nucleus of an atom [1]

⚠ If you missed marks here: Neutrons = nucleon number − proton number = 23 − 11 = 12; giving 23 confuses the nucleon number with the neutron count. The proton number is the number of protons IN THE NUCLEUS – defining it as "the number of electrons" or "protons plus neutrons" (that is the nucleon number) loses the mark.

1 mark -- protons eleven electrons eleven 1 mark -- neutrons twelve 1 mark -- proton number is number protons nucleus atom

Question 2 -- Atomic Structure and Electronic Configurations

Total: 12 marks

A student in Bangalore studies the first 20 elements of the Periodic Table and their electronic configurations.

(a) [4]

Write the electronic configuration of each of the following atoms.

(i) Carbon (Z = 6)
(ii) Aluminium (Z = 13)
(iii) Argon (Z = 18)
(iv) Calcium (Z = 20)

Model Answer -- 2(a)

Carbon: 2, 4 [1]

Aluminium: 2, 8, 3 [1]

Argon: 2, 8, 8 [1]

Calcium: 2, 8, 8, 2 [1]

⚠ If you missed marks here: Calcium is 2,8,8,2, not 2,8,10: for the first 20 elements the third shell takes 8, and calcium's last two electrons start a fourth shell, which is why it is in Group II. Check each answer by adding the numbers back up to the proton number (2 + 8 + 3 = 13 for aluminium).

1 mark -- carbon 2 4 1 mark -- aluminium 2 8 3 1 mark -- argon 2 8 8 1 mark -- calcium 2 8 8 2

(b) [3]

Using your answers to part (a):

(i) Explain how the electronic configuration of an element relates to its group number in the Periodic Table. [1]

(ii) Explain how the electronic configuration of an element relates to its period number in the Periodic Table. [1]

(iii) State the group and period of aluminium. [1]

Model Answer -- 2(b)

The group number equals the number of electrons in the outer shell / outermost energy level [1]

The period number equals the number of occupied electron shells / energy levels [1]

Aluminium is in Group III / Group 13 and Period 3 [1]

⚠ If you missed marks here: The two rules are easy to swap: outer-shell electrons give the GROUP, the number of occupied shells gives the PERIOD. Aluminium (2,8,3) has 3 outer electrons and 3 shells, so it is Group III and Period 3 – not Period 13 from its proton number.

1 mark -- group number equals electrons outer shell 1 mark -- period number equals number occupied electron shells 1 mark -- aluminium group three period three

Draw the electronic structure (electron shell diagram) of a silicon atom (Z = 14). Show the nucleus and the arrangement of electrons in shells.

Model Answer -- 2(c)

Silicon: 2, 8, 4 -- correct number of electrons in each shell [1]

Nucleus labelled with 14p and 14n (or just labelled correctly) [1]

⚠ If you missed marks here: Silicon (proton number 14) needs 2 electrons in the first shell, 8 in the second and 4 in the third – count your crosses, as 2,8,3 and 2,8,5 drawings are common slips. Label the nucleus (14 protons and 14 neutrons); leaving it unlabelled, or putting electrons inside it, loses the second mark.

1 mark -- correct electrons 2 8 4 shown shells 1 mark -- nucleus labelled protons neutrons

(d) [3]

An element X has the electronic configuration 2, 8, 7.

(i) Identify element X. [1]

(ii) State the group and period of element X. [1]

(iii) Predict whether element X is a metal or a non-metal. Explain your answer. [1]

Model Answer -- 2(d)

Element X is chlorine (Cl) -- proton number = 2 + 8 + 7 = 17 [1]

Group VII / Group 17, Period 3 [1]

Non-metal, because it is in Group VII / has 7 outer electrons so it gains electrons rather than losing them / is on the right side of the Periodic Table [1]

⚠ If you missed marks here: Add up the electrons to get the proton number: 2 + 8 + 7 = 17, which is chlorine – naming nitrogen (proton number 7) uses only the outer-shell count. For (iii), "non-metal" needs a reason: with 7 outer electrons, chlorine gains one electron to fill its outer shell, whereas metals lose electrons.

1 mark -- chlorine identified 1 mark -- group seven period three 1 mark -- non-metal gains electrons right side periodic table

Question 3 -- Isotopes

Total: 12 marks

Copper is widely used in electrical wiring throughout India and the United Kingdom. Natural copper consists of two isotopes: ⁶³Cu and ⁶⁵Cu.

(a) [2]

Define the term isotopes.

Model Answer -- 3(a)

Isotopes are atoms of the same element [1]

with the same number of protons but different numbers of neutrons / different mass numbers [1]

⚠ If you missed marks here: Isotopes have the SAME number of protons (so they are the same element) and DIFFERENT numbers of neutrons – swapping protons and neutrons, or saying the electrons differ, loses the marks. "Atoms with different masses" is not enough on its own, because atoms of different elements also have different masses.

1 mark -- atoms same element 1 mark -- same protons different neutrons

(b) [3]

Copper has a proton number of 29.

(i) State the number of protons, neutrons and electrons in an atom of ⁶³Cu. [2]

(ii) Write the full nuclide notation for the isotope copper-65. [1]

Model Answer -- 3(b)

Protons = 29, Electrons = 29 [1]

Neutrons = 63 − 29 = 34 [1]

⁶⁵₂₉Cu -- mass number 65 at top, proton number 29 at bottom [1]

⚠ If you missed marks here: Neutrons = 63 − 29 = 34, not 63. In nuclide notation the nucleon number (65) goes at the TOP left of the symbol and the proton number (29) at the BOTTOM left; writing them the other way up loses the mark.

1 mark -- protons 29 electrons 29 1 mark -- neutrons 34 1 mark -- nuclide notation 65 top 29 bottom Cu

Explain why the two isotopes of copper have the same chemical properties.

Model Answer -- 3(c)

Both isotopes have the same number of electrons / the same electronic configuration [1]

Chemical properties depend on the arrangement of electrons / the number of outer shell electrons, which is the same in both isotopes [1]

⚠ If you missed marks here: "They have the same number of protons" is true but scores nothing on its own – chemical reactions involve ELECTRONS, so say both isotopes have the same number of electrons arranged in the same way. The extra neutrons only change the mass, which does not affect how the atom reacts.

1 mark -- same number electrons same electronic configuration 1 mark -- chemical properties depend electron arrangement outer shell

(d) [3]

A sample of copper contains 69.2% of ⁶³Cu and 30.8% of ⁶⁵Cu.

Calculate the relative atomic mass (A_r) of copper. Give your answer to one decimal place.

Model Answer -- 3(d)

A_r = (69.2 × 63) + (30.8 × 65) / 100 [1] -- correct formula set up

A_r = (4359.6 + 2002.0) / 100 = 6361.6 / 100 [1] -- correct working

A_r = 63.6 [1] -- correct final answer to 1 decimal place

⚠ If you missed marks here: A relative atomic mass is a WEIGHTED average, so (63 + 65) ÷ 2 = 64 is wrong – copper-63 is more than twice as common and pulls the answer down to 63.6. Divide the total by 100 and give one decimal place as asked; rounding to 64 loses the last mark.

1 mark -- correct formula abundances multiplied masses 1 mark -- correct arithmetic working 1 mark -- answer 63.6

(e) [2]

Suggest one physical property in which the two isotopes of copper would differ. Explain your answer.

Model Answer -- 3(e)

Density / rate of diffusion / mass [1] -- any valid physical property

⁶⁵Cu is heavier / has more neutrons / greater mass, so it would have a higher density / diffuse more slowly [1]

⚠ If you missed marks here: Choose a property that depends on MASS, such as density or rate of diffusion, and link it to the two extra neutrons in copper-65. Reactivity is a chemical property and is the same for both isotopes, and properties such as colour have no link to the extra neutrons, so neither scores.

1 mark -- valid physical property density diffusion mass 1 mark -- explanation linked different neutrons different mass

Question 4 -- Ionic Bonding

Total: 12 marks

Magnesium oxide (MgO) is used in fire bricks in steel furnaces across Sheffield. It has a very high melting point of 2852 °C.

(a) [3]

(i) Define the terms cation and anion. [2]

(ii) State the charge on a magnesium ion and an oxide ion. [1]

Model Answer -- 4(a)

A cation is a positively charged ion / an ion formed by loss of electrons [1]

An anion is a negatively charged ion / an ion formed by gain of electrons [1]

Magnesium ion: Mg²⁺, Oxide ion: O²⁻ [1]

⚠ If you missed marks here: Cations are POSITIVE (formed by losing electrons) and anions NEGATIVE (formed by gaining electrons) – swapping the two loses both definition marks. Magnesium (Group II) loses 2 electrons to give Mg²⁺ and oxygen (Group VI) gains 2 to give O²⁻; writing O₂ (the molecule) or O⁻ loses the last mark.

1 mark -- cation positively charged ion loss electrons 1 mark -- anion negatively charged ion gain electrons 1 mark -- magnesium 2+ oxide 2-

(b) [3]

(i) Define an ionic bond. [1]

(ii) Describe what happens to the electrons when magnesium reacts with oxygen to form magnesium oxide. [2]

Model Answer -- 4(b)

An ionic bond is the electrostatic attraction between oppositely charged ions / a strong force of attraction between a positive ion and a negative ion [1]

Magnesium atom loses 2 electrons from its outer shell to form Mg²⁺ [1]

Oxygen atom gains these 2 electrons into its outer shell to form O²⁻ / to achieve a stable octet [1]

⚠ If you missed marks here: An ionic bond is the electrostatic attraction between oppositely charged IONS – "sharing electrons" describes a covalent bond, and "attraction between atoms" misses the charges. For the electrons, the metal gives them away: each magnesium atom loses its 2 outer electrons, and an oxygen atom gains both to fill its outer shell.

1 mark -- ionic bond electrostatic attraction oppositely charged ions 1 mark -- magnesium loses two electrons outer shell 1 mark -- oxygen gains two electrons stable octet

Draw a dot-and-cross diagram to show the ionic bonding in magnesium oxide (MgO). Show the charges on the ions and the electronic configuration of the ions formed.

Mg: 2, 8, 2 O: 2, 6

Model Answer -- 4(c)

Mg²⁺ shown with electronic configuration 2, 8 (lost 2 outer electrons) [1]

O²⁻ shown with electronic configuration 2, 8 (gained 2 electrons) [1]

Transferred electrons clearly distinguished (dots vs crosses) with correct charges on ions [1]

⚠ If you missed marks here: Do not draw Mg and O overlapping or sharing a pair – magnesium oxide is ionic, so show two separate ions with their charges, Mg²⁺ and O²⁻. The oxide ion must end with 8 outer electrons, its own 6 plus the 2 from magnesium, drawn with a different symbol so the transfer can be seen.

1 mark -- magnesium ion 2 8 configuration lost two electrons 1 mark -- oxide ion 2 8 configuration gained two electrons 1 mark -- transferred electrons distinguished dots crosses charges shown

(d) [3]

Magnesium oxide has a high melting point and conducts electricity when molten but not when solid.

(i) Describe the structure of magnesium oxide. [1]

(ii) Explain why magnesium oxide has a high melting point. [1]

(iii) Explain why magnesium oxide conducts electricity when molten but not when solid. [1]

Model Answer -- 4(d)

Magnesium oxide has a giant ionic lattice structure -- a regular arrangement of alternating Mg²⁺ and O²⁻ ions [1]

High melting point because there are strong electrostatic forces of attraction between the oppositely charged ions, which require a large amount of energy to overcome [1]

When solid, ions are held in fixed positions and cannot move to carry charge; when molten, the ions are free to move and carry the electric current [1]

⚠ If you missed marks here: In molten magnesium oxide it is the IONS that move and carry the current – "free electrons" is the explanation for a metal and scores nothing here. Likewise, the high melting point comes from strong electrostatic attraction between oppositely charged ions throughout a giant lattice; "molecules" or "intermolecular forces" lose the mark, because magnesium oxide has no molecules.

1 mark -- giant ionic lattice regular arrangement ions 1 mark -- strong electrostatic attraction oppositely charged ions large energy overcome 1 mark -- solid ions fixed cannot move molten ions free move carry current

Question 5 -- Covalent Bonding

Total: 10 marks

Water is essential for life. A researcher at the Indian Institute of Science in Bengaluru studies the bonding in water and other simple covalent molecules.

(a) [1]

Define a covalent bond.

Model Answer -- 5(a)

A covalent bond is a shared pair of electrons between two atoms [1]

⚠ If you missed marks here: The mark needs a shared PAIR of electrons between two ATOMS – "atoms share electrons" without the word pair, or "a bond between ions", does not score. "Transfer of electrons" describes ionic bonding.

1 mark -- shared pair electrons between two atoms

(b) [4]

Draw dot-and-cross diagrams to show the covalent bonding in each of the following molecules. Show outer shell electrons only.

(i) Water, H₂O [1]
(ii) Methane, CH₄ [1]
(iii) Carbon dioxide, CO₂ [1]
(iv) Nitrogen, N₂ [1]

Model Answer -- 5(b)

(i) Water, H₂O

(ii) Methane, CH₄

(iii) Carbon dioxide, CO₂ (double bonds)

(iv) Nitrogen, N₂ (triple bond)

H₂O: 2 shared pairs between O and H atoms, 2 lone pairs on O, each H has 2 electrons [1]

CH₄: 4 shared pairs between C and H atoms, C achieves an octet [1]

CO₂: 2 double bonds (O=C=O), each O has 2 lone pairs, C achieves an octet [1]

N₂: triple bond (3 shared pairs), each N has 1 lone pair [1]

⚠ If you missed marks here: Count to 8 around every atom except hydrogen (which has 2): CO₂ needs TWO shared pairs between carbon and each oxygen, and N₂ needs THREE – single bonds leave atoms short and lose the mark. Do not forget the lone pairs: two on the oxygen in water, two on each oxygen in CO₂ and one on each nitrogen.

1 mark -- water correct two shared pairs two lone pairs oxygen 1 mark -- methane correct four shared pairs carbon octet 1 mark -- carbon dioxide correct two double bonds lone pairs oxygen 1 mark -- nitrogen correct triple bond lone pair each nitrogen

Simple covalent substances such as water and methane have low melting and boiling points.

(i) State whether simple covalent molecules conduct electricity. [1]

(ii) Explain why simple covalent substances have low boiling points. [2]

Model Answer -- 5(c)

Simple covalent substances do not conduct electricity as solids or liquids (poor electrical conductivity), because their molecules are uncharged: there are no ions or delocalised electrons free to move and carry the current [1]

Note: do not add "or in solution" – some simple covalent substances, such as hydrogen chloride and ammonia, react with water to form ions, so their solutions do conduct.

The intermolecular forces (forces between molecules) are weak [1]

Only a small amount of energy is needed to overcome these weak intermolecular forces, so the boiling point is low (note: the strong covalent bonds within molecules are NOT broken) [1]

⚠ If you missed marks here: Boiling water does not break its O–H covalent bonds, which are strong, so "the covalent bonds are weak" loses both explanation marks: it is the WEAK forces BETWEEN the molecules that are overcome, and that needs little energy. For (i), give the reason the pure substance does not conduct – no ions and no delocalised electrons to carry charge. Do not claim it never conducts "even in solution": hydrogen chloride and ammonia form ions in water.

1 mark -- do not conduct no free ions no delocalised electrons 1 mark -- weak intermolecular forces between molecules 1 mark -- small energy overcome weak forces boiling point low

(d) [2]

Methanol has the molecular formula CH₃OH.

(i) State the total number of covalent bonds in one molecule of methanol. [1]

(ii) State the total number of lone pairs of electrons in one molecule of methanol. [1]

Model Answer -- 5(d)

5 covalent bonds (3 C–H bonds + 1 C–O bond + 1 O–H bond) [1]

2 lone pairs (both on the oxygen atom) [1]

⚠ If you missed marks here: Draw the molecule before counting: three C–H, one C–O and one O–H make 5 covalent bonds (4 means one was missed). The oxygen has 6 outer electrons, uses 2 of them in bonds and keeps 4 as TWO lone pairs – answering 4 counts the electrons, not the pairs.

1 mark -- five covalent bonds 1 mark -- two lone pairs oxygen

Question 6 -- Giant Covalent Structures

Total: 12 marks

Diamond and graphite are both allotropes of carbon. They are used in drill bits for mining in South Africa and as lubricants in heavy machinery, respectively.

(a) [3]

(i) Describe the structure of diamond. [2]

(ii) State one use of diamond, linked to its properties. [1]

Model Answer -- 6(a)

Diamond has a giant covalent structure / giant molecular structure / macromolecular structure [1]

Each carbon atom is bonded to four other carbon atoms by strong covalent bonds in a tetrahedral arrangement [1]

Use: cutting tools / drill bits / jewellery -- because diamond is the hardest natural substance / very hard [1]

⚠ If you missed marks here: Each carbon in diamond is bonded to FOUR others (three is graphite) in a giant tetrahedral network – describing small separate molecules or flat layers loses the structure marks. The use must come with its reason: cutting tools or drill bits, because diamond is extremely hard; a use with no property attached does not score.

1 mark -- giant covalent structure 1 mark -- each carbon bonded four others tetrahedral covalent bonds 1 mark -- use linked property cutting hardest

(b) [4]

(i) Describe the structure of graphite. [3]

(ii) State one use of graphite, linked to its properties. [1]

Model Answer -- 6(b)

Graphite has a giant covalent / layered structure with each carbon atom bonded to three other carbon atoms in flat hexagonal layers [1]

There are weak intermolecular forces / weak van der Waals forces between the layers, so the layers can slide over each other [1]

Each carbon atom has one delocalised electron which is free to move along (within) the layers, so graphite conducts electricity [1]

Use: lubricant (because layers slide) / electrodes (because it conducts electricity) / pencil leads (because layers slide off onto paper) [1]

⚠ If you missed marks here: The bonds WITHIN each layer are strong covalent bonds, but the forces BETWEEN the layers are weak – mixing these up ("weak covalent bonds" or "strong bonds between layers") loses the sliding mark. Graphite conducts because each carbon has one delocalised electron that is free to move ALONG its layer, not because of ions; "the electrons move between the layers" puts them in the wrong place.

1 mark -- each carbon bonded three others hexagonal layers 1 mark -- weak forces between layers layers slide 1 mark -- delocalised electrons free move conducts electricity 1 mark -- use linked property lubricant electrodes pencils

(i) Explain why diamond does not conduct electricity but graphite does. [1]

(ii) Explain why both diamond and graphite have very high melting points. [1]

Model Answer -- 6(c)

In diamond all four outer electrons of each carbon are used in covalent bonds so there are no delocalised / free electrons; in graphite each carbon uses only three electrons for bonding, leaving one electron delocalised and free to move and carry current [1]

Both have many strong covalent bonds throughout the structure which require a large amount of energy to break [1]

⚠ If you missed marks here: Melting either solid means breaking strong COVALENT bonds throughout the giant structure – "strong intermolecular forces" is wrong for both, and the weak forces between graphite's layers do not give it a low melting point. For conduction, compare the electrons: diamond uses all four outer electrons in bonds, graphite only three, leaving one delocalised electron per carbon.

1 mark -- diamond no delocalised electrons graphite delocalised electrons free move 1 mark -- both many strong covalent bonds large energy break

(d) [3]

Silicon dioxide (SiO₂) is found in sand and is used to make glass.

(i) Describe the structure of silicon dioxide. [2]

(ii) Predict the melting point of silicon dioxide (high or low) and explain your answer. [1]

Model Answer -- 6(d)

Silicon dioxide has a giant covalent structure similar to diamond [1]

Each silicon atom is bonded to four oxygen atoms by strong covalent bonds, and each oxygen atom is bonded to two silicon atoms, forming a three-dimensional network [1]

High melting point because there are many strong covalent bonds throughout the structure that require a large amount of energy to break [1]

⚠ If you missed marks here: SiO₂ is NOT a small molecule like CO₂: it is a giant covalent network in which each silicon bonds to FOUR oxygens and each oxygen to TWO silicons, which is where the 1 : 2 formula comes from. Predicting a low melting point, or explaining a high one with "intermolecular forces", loses the mark – melting it means breaking many strong covalent bonds.

1 mark -- giant covalent structure similar diamond 1 mark -- silicon bonded four oxygens oxygen bonded two silicons network 1 mark -- high melting point strong covalent bonds large energy

Question 7 -- Metallic Bonding

Total: 10 marks

Copper is widely used for electrical wiring in homes across Mumbai. Aluminium is used in aircraft manufacturing by companies such as Airbus in Toulouse, France. Both are metals with characteristic properties.

(a) [3]

Describe metallic bonding. You may include a labelled diagram to support your answer.

Model Answer -- 7(a)

Metal atoms lose their outer shell electrons to form positive ions / cations [1]

These electrons become delocalised / free to move throughout the structure, forming a "sea" of electrons [1]

There is a strong electrostatic attraction between the positive metal ions and the delocalised electrons -- this is the metallic bond [1]

⚠ If you missed marks here: There are no negative IONS in a metal: the bond is the attraction between POSITIVE metal ions and a sea of delocalised ELECTRONS. "Attraction between atoms" or "metal atoms share electrons" describes the wrong kind of bonding and loses the third mark.

1 mark -- metal atoms lose outer electrons form positive ions 1 mark -- electrons delocalised free move sea electrons 1 mark -- strong electrostatic attraction positive ions delocalised electrons

(b) [2]

Explain why metals are good conductors of electricity.

Model Answer -- 7(b)

Metals contain delocalised electrons that are free to move throughout the metal structure [1]

When a potential difference / voltage is applied, these electrons drift towards the positive terminal, carrying the electric current [1]

⚠ If you missed marks here: In a solid metal the positive ions stay fixed in the lattice – it is the delocalised ELECTRONS that move through the structure and carry the charge, so "the ions are free to move" is wrong. Use the precise words delocalised (or free) electrons; "the metal has spare electrons" is too vague for the mark.

1 mark -- delocalised electrons free move throughout structure 1 mark -- electrons drift carry electric current voltage applied

Metals are described as malleable (can be hammered into shape) and ductile (can be drawn into wires).

(i) Define the term malleable. [1]

(ii) Explain, in terms of structure and bonding, why metals are malleable. [2]

Model Answer -- 7(c)

Malleable means the metal can be hammered or pressed into different shapes without breaking [1]

The layers of positive ions / metal ions can slide over each other when a force is applied [1]

The delocalised electrons continue to hold the ions together / the metallic bond is maintained in the new positions, so the metal does not shatter [1]

⚠ If you missed marks here: Malleable means it can be hammered or pressed into shape without breaking – "can be drawn into wires" is ductile, a different property. In the explanation, the metallic bonding is not weak: the layers of positive ions slide over each other, and the delocalised electrons keep attracting the ions in their new positions, so the metal changes shape instead of shattering.

1 mark -- malleable hammered pressed shapes without breaking 1 mark -- layers positive ions slide over each other force 1 mark -- delocalised electrons hold ions together bond maintained new positions

(d) [2]

The table below compares three types of bonding. Complete the table.

Property	Ionic	Simple covalent	Metallic
Conducts electricity as solid?	No	No	.......
Melting point	.......	Low	High

Model Answer -- 7(d)

Metallic solid conducts electricity: Yes [1]

Ionic melting point: High [1]

⚠ If you missed marks here: The gap in the melting-point row is under IONIC, and ionic compounds have HIGH melting points (strong attraction between ions throughout the lattice) – "low" is the simple covalent entry already printed beside it. Metals DO conduct as solids, because their delocalised electrons move even though the ions are fixed.

1 mark -- metallic conducts electricity yes 1 mark -- ionic melting point high

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