Ch 7 · Metallic Bonding · IGCSE Chemistry 0620
Topic 7 of 7 in Atoms, Elements and Compounds — IGCSE Chemistry 0620 — 48 lessons.
Introduction
Metals conduct electricity, bend without breaking and can be hammered into sheets, properties that neither ionic nor simple covalent substances share. The explanation is a third type of bonding, in which the outer electrons of every atom are pooled. This lesson completes the picture of bonding by comparing all three types side by side, a comparison that Core candidates must know even though the metallic model itself is Extended content.
Key ideas — The metallic bond
🧑🏫 Teacher's explanation
Imagine a crowded dance floor where everyone is holding onto a large, shared silk sheet. The dancers are the positive metal ions, and the silk sheet represents the sea of delocalised electrons. Because the sheet is being pulled by everyone simultaneously, it holds the dancers together in a structured way, but it also allows them to move around easily without the whole group falling apart.
📖 Definitions
🔍 Worked example — Easy
Explain why magnesium (Mg) has a high melting point based on its bonding.
🔍 Worked example — Standard
A sample of copper contains 6.02 × 10^23 copper ions. If each ion is surrounded by 12.6 delocalised electrons, calculate the total number of delocalised electrons in the sample.
🔍 Worked example — Exam-style
Compare the electrical conductivity of a metal to that of an ionic compound (like NaCl) in the solid state.
⚠️ Common errors
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🎯 Exam question
Key ideas — Explaining the properties of metals
🧑🏫 Teacher's explanation
Imagine a crowded ballroom where everyone is holding onto a long, flowing silk ribbon. The people are the positive metal ions, and the ribbon is the sea of delocalised electrons. Because the ribbon is continuous and flexible, if you push one person, the ribbon pulls everyone along with them. This 'fluidity' is why metals can be shaped without snapping.
📖 Definitions
🔍 Worked example — Easy
Explain why solid magnesium conducts electricity, but solid sodium chloride does not.
🔍 Worked example — Standard
A sample of copper contains 6.02 × 10^23 atoms. If the charge of an electron is 1.6 × 10^-19 C, calculate the total charge of the delocalised electrons if each atom contributes one electron.
🔍 Worked example — Exam-style
Explain why metals are malleable using the term 'layers'.
⚠️ Common errors
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🎯 Exam question
(a) Explain why Iron is malleable. (b) Explain why Magnesium Oxide is brittle and does not conduct electricity when solid. [4 marks]
Key ideas — Comparing the three types of bonding
Every candidate must be able to compare the three bonding types. Read the table row by row: what particles are present, what holds them together, and what properties result.
🧑🏫 Teacher's explanation
Imagine a large crowd of people (the positive ions) all standing in a grid, but everyone has lost their keys (the valence electrons). Instead of holding the keys, the keys are floating freely around the crowd like a swarm of bees. Because the keys are moving everywhere, they act like a 'glue' that holds the people together.
📖 Definitions
🔍 Worked example — Easy
Explain why magnesium (Mg) has a high melting point.
🔍 Worked example — Standard
Explain why copper (Cu) is malleable.
🔍 Worked example — Exam-style
Compare the electrical conductivity of Sodium (Na) and Carbon Dioxide (CO_2) in the solid state.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
(a) Explain why Iron conducts electricity in the solid state, but Sodium Chloride does not. [2] (b) Explain why Iron is malleable, whereas Sodium Chloride is brittle. [2] [4 marks]
Key ideas — Deciding the bonding type from data
Exam questions often give the properties of an unknown substance and ask you to identify its bonding. Use this order of questions:
🧑🏫 Teacher's explanation
Imagine a crowded ballroom where everyone is holding hands tightly. If everyone is holding hands, the group is rigid and hard to change (like a giant covalent structure). Now, imagine a room full of people running around wildly, but they are all carrying magnets. The magnets (positive ions) are attracted to each other, but because the people (electrons) are moving everywhere, the whole group can flow and shift without breaking the magnetic attraction. This is metallic bonding.
📖 Definitions
🔍 Worked example — Easy
A white crystalline solid has a melting point of 801^° C. It does not conduct electricity in the solid state, but it conducts electricity when dissolved in water. Identify the bonding type.
🔍 Worked example — Standard
A substance is a grey solid. It conducts electricity very well in the solid state. It is very malleable. Identify the bonding type.
🔍 Worked example — Exam-style
Substance X has a very low melting point of -103^° C. It does not conduct electricity in any state. Identify the bonding type.
⚠️ Common errors
🧠 Quick check 1
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🎯 Exam question
Worked example
Question. Copper is used for electrical wiring and can be hammered into thin sheets.
🔍 Worked example — Easy
Identify the bonding type in a substance composed of a regular arrangement of positive ions surrounded by a mobile cloud of electrons.
🔍 Worked example — Standard
Explain why magnesium (Mg) is a good conductor of electricity.
🔍 Worked example — Exam-style
Compare the bonding in Sodium (Na) and Carbon (C) in diamond. Which is more likely to be brittle and why?
⚠️ Common errors
Common mistakes
Practice
Answers The electrostatic attraction between the positive ions in a giant metallic lattice [B1] and the sea of delocalised electrons [B1]. The layers of positive ions can slide over one another when a force is applied [B1]; the delocalised electrons move with them, so the metallic bonding is maintained and the structure does not break [B1]. Metals conduct electricity when solid but ionic compounds do not (or: metals are malleable but ionic compounds are brittle) [B1]; in a metal delocalised electrons are free to move and carry charge [B1]; in a solid ionic compound the ions are held in fixed positions and cannot move [B1]. Sodium chloride: ionic, does not conduct as a solid [B1]; water: covalent (simple molecular), does not conduct [B1]; iron: metallic, conducts as a solid [B1].