IB DP Chemistry Structure 2.3: The metallic model – 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 – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

Test Structure 2.3, The metallic model, as defined in the IB Diploma Programme Chemistry guide (February 2023 edition, examined from 2025). Questions 1 to 5 cover understanding 2.3.1, questions 6 to 9 cover 2.3.2, and question 10 combines both. These are for SL and HL. Question 11 covers 2.3.3, which is additional higher level, so it is HL only.

Learning the metallic model for the first time? Start with the Structure 2.3 study guide. Want only a recap? The metallic model revision notes cover it in brief. For the wider course, see the course page for IB DP chemistry, a printable checklist and free diagnostics.

Questions

1. Define the term metallic bond. [2]

2. Mercury is a metal that is a liquid at 298 K.

(a) Explain why liquid mercury conducts electricity. [2] (b) Molten sodium chloride also conducts electricity. Identify the particles that carry the charge in molten sodium chloride and in liquid mercury. [2]

3. A jeweller hammers a bar of silver into a thin sheet. When a crystal of calcium fluoride is struck with a hammer, it shatters.

(a) Explain why silver can be hammered into a new shape. [2] (b) Explain why the calcium fluoride crystal shatters instead. [2]

4. A copper spoon is placed in a cup of hot tea. Within a few seconds the end of the handle feels warm. Explain this observation in terms of the bonding in copper. [2]

5. For each use below, state one property of the metal that makes it suitable, and explain that property using the metallic model.

(a) Copper pipes in a heating system, which a plumber bends to fit around corners [2] (b) Aluminium sheet that is pressed into the shape of a drinks can [2]

6. Use these melting points of three group 2 metals.

Metal	Ca	Sr	Ba
Melting point / K	1115	1050	1000

Describe and explain the trend in melting point down this part of group 2. [3]

7. Rubidium is in group 1 and strontium is in group 2. Both are in period 5. Use these values, and take the Avogadro constant as 6.02 × 10²³ mol⁻¹.

Metal	Density / g cm⁻³	Molar mass / g mol⁻¹
Rb	1.53	85.47
Sr	2.64	87.62

(a) Calculate the amount, in mol, of atoms in 1.00 cm³ of each metal. [2] (b) Calculate the number of delocalized electrons in 1.00 cm³ of each metal. [2] (c) Use your answers to state which metal has the higher melting point. [1]

8. Arrange caesium, rubidium and strontium in order of increasing melting point. Explain your order. [3]

9. Aluminium (group 13, period 3) melts at 933 K. Gallium, directly below it in group 13, melts at 303 K. Both form 3+ ions.

(a) State the trend the simple metallic model predicts for melting point down a group. [1] (b) Suggest what these data show about the simple model when it is applied to p-block metals. [1]

10. An engineer is choosing a metal for a heat sink, a finned block that draws heat away from a laptop processor. The heat sink has a volume of 50.0 cm³. Use these values.

Metal	Density / g cm⁻³	Thermal conductivity / W m⁻¹ K⁻¹
Copper	8.96	401
Aluminium	2.70	237

(a) Calculate the mass of the heat sink if it is made from each metal. [2] (b) Explain, in terms of bonding, why both metals are good thermal conductors. [2] (c) The fins are made by pressing the metal into thin sheets. Explain why this is possible. [2] (d) Suggest, with a reason based on the data, which metal is the better choice for a portable laptop. [2]

11. HL only. This question is about period 4 elements.

Element	Ca	V	Zn
Melting point / K	1115	2183	693

(a) Write the valence electron configuration of calcium and of vanadium. [2] (b) Explain why vanadium has a much higher melting point than calcium. [3] (c) Explain why vanadium is a good conductor of electricity. [1] (d) Zinc has the valence configuration 3d¹⁰ 4s². Suggest why its melting point is much lower than that of vanadium. [1]

Answers

1. An electrostatic attraction [1] that holds a lattice of positive metal ions (cations) to the delocalized electrons around them [1]. [2] Examiner insight: Name both parts of the structure and the type of force; a definition that mentions only “a sea of electrons” leaves out what the electrons are attracted to.

2. (a) Mercury still contains delocalized electrons after melting [1]; these are mobile and move when a potential difference is applied, so charge flows [1]. (b) Molten sodium chloride: ions (Na⁺ and Cl⁻) [1]. Liquid mercury: delocalized electrons [1]. Examiner insight: State the charge carrier by name in each case; “charged particles” for both does not show that you know the difference between ionic and metallic conduction.

3. (a) When the force is applied, layers of silver cations slide over one another [1]; the delocalized electrons move with them, so the non-directional attraction between cations and electrons is kept and the metal does not break [1]. (b) In the ionic lattice, sliding brings ions of the same charge next to each other [1]; they repel strongly, so the crystal splits apart [1]. Examiner insight: “Layers slide” on its own explains only half of malleability; you also need the reason the metal stays bonded after the layers move.

4. The delocalized electrons in the copper near the tea gain kinetic energy [1]; because they are mobile they move quickly along the handle and pass the energy on through collisions, so the far end warms up [1]. [2] Examiner insight: Thermal conductivity answers should mention energy being carried, not just “electrons can move”, which is the explanation for electrical conductivity.

5. (a) Copper is malleable (or ductile), so the pipe bends without cracking [1]; layers of cations slide while the delocalized electrons keep attracting them [1]. (Good thermal conductivity, explained by mobile electrons carrying kinetic energy, is an acceptable alternative.) (b) Aluminium is malleable [1]; the bonding is non-directional, so layers of Al³⁺ cations can move over each other and stay held by the electron cloud as the sheet is shaped [1]. Examiner insight: Match the property to the use described; for a can that is pressed into shape, a reason based on electrical conductivity does not answer the question.

6. Melting point decreases from calcium to barium [1]. All three form 2+ cations, but the ion radius increases down the group [1], so the attraction between the cations and the delocalized electrons is weaker and less energy is needed to melt the metal [1]. [3] Examiner insight: “Describe” asks for the trend itself, so say that the melting point falls before you explain it; the charge staying the same is part of the explanation.

7. (a) Mass of 1.00 cm³ = density × volume; n = m / M. Rb: 1.53 / 85.47 = 0.0179 mol [1] Sr: 2.64 / 87.62 = 0.0301 mol [1]

(b) Rb: 0.0179 × 6.02 × 10²³ × 1 = 1.08 × 10²² delocalized electrons [1] Sr: 0.0301 × 6.02 × 10²³ × 2 = 3.63 × 10²² delocalized electrons [1] (Rounding the Sr amount early gives 3.62 × 10²², which is also reasonable.)

(c) Strontium, because it has the higher electron density (more than three times as many delocalized electrons per cm³) as well as the higher cation charge [1]. Examiner insight: Show the multiplication by the number of electrons each atom releases; quoting the number of atoms as the number of electrons for strontium is a common slip that changes the answer.

8. Order: caesium < rubidium < strontium [1]. Cs⁺ and Rb⁺ both have a 1+ charge, but Cs⁺ is larger, so its metallic bonding is weaker than that of rubidium [1]. Sr forms Sr²⁺, which has a higher charge, gives two delocalized electrons per atom and is smaller than Rb⁺, so strontium has the strongest metallic bonding [1]. [3] Examiner insight: Check the direction the question asks for; “increasing” means lowest first, and a correct order written in reverse gives the wrong answer.

9. (a) Melting point should decrease down a group, because the ions get larger while the charge stays the same [1]. (b) Gallium melts far lower than expected, so the model in terms of charge and radius does not fully explain the melting points of p-block metals [1]. Examiner insight: A “suggest” answer needs a reasoned idea, not detailed knowledge of gallium; say plainly that the data limit the model.

10. (a) mass = density × volume Copper: 8.96 × 50.0 = 448 g [1] Aluminium: 2.70 × 50.0 = 135 g [1]

(b) Both metals contain delocalized electrons that are free to move [1]; they gain kinetic energy near the processor and carry it rapidly through the metal to the fins [1].

(c) The metallic bonding is non-directional [1]; when the metal is pressed, layers of cations slide and the delocalized electrons move with them, so the metal flattens into sheets without breaking [1].

(d) Aluminium [1]. Copper conducts heat only about 1.7 times better (401 / 237), but the copper heat sink is about 3.3 times heavier (448 g against 135 g), and low mass matters in a portable device [1]. Examiner insight: When asked to use the data, quote numbers from the table or your calculation; a choice supported only by “aluminium is lighter” uses less of the evidence than one that weighs both properties.

11. (a) Ca: 4s² [1]; V: 3d³ 4s² [1]. (b) In vanadium, the 3d electrons as well as the 4s electrons can be delocalized [1], so there are more delocalized electrons per atom and a higher electron density than in calcium [1]. The attraction between the small, highly charged cations and the delocalized electrons is stronger, so more energy is needed to disrupt the lattice [1]. (c) The delocalized 4s and 3d electrons are mobile and can carry charge through the lattice [1]. (d) Zinc’s full 3d sublevel contributes little to the delocalized electrons, so its metallic bonding is weaker [1]. Examiner insight: The key HL idea is that d-electrons join the delocalized cloud; an answer that explains vanadium’s melting point using only its 4s electrons gives no reason why it differs from calcium.

Where marks are usually lost

• Describing a metal as “positive and negative ions” or as “atoms in a sea of electrons” instead of cations and delocalized electrons.
• Leaving out the word attraction: the bond is the electrostatic attraction, not the electrons themselves.
• Saying cations move when a solid metal conducts electricity.
• Giving the electrical conductivity explanation for a thermal conductivity question, with no mention of energy transfer.
• Stopping at “layers slide” for malleability and not saying why the metal stays bonded.
• Comparing melting points using only one factor, especially across a period where charge and radius both change.
• In calculations, forgetting to multiply by the number of electrons released per atom, or rounding too early.
• Not using the data supplied when a question says to.
• (HL only) Ignoring the 3d electrons when explaining transition element properties.

Next steps

• Find your weak spots first with all free 10-minute diagnostics
• Recap the key points: metallic model revision notes
• Relearn a weak area: metallic model study guide
• Browse other units: the chemistry course page
• Track your revision: DP chemistry checklist
• Book a free trial class if you would like live help on bonding

Official syllabus

This set is written to the DP Chemistry guide that the International Baccalaureate published in February 2023, first assessed in 2025. They target sub-topic Structure 2.3, The metallic model: understandings 2.3.1 and 2.3.2 (SL and HL) and 2.3.3 (additional higher level, HL only).