Bonding and Structure
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2.1 Ionic bonding
Ionic bonding is the strong electrostatic attraction between oppositely charged ions, formed when electrons transfer from a metal to a non-metal.
Metals lose electrons to form positive ions; non-metals gain electrons to form negative ions, usually reaching a noble-gas configuration. In a dot-and-cross diagram, show the electrons from each atom with different symbols, put square brackets round each ion, and write the charge outside.
The ions sit in a giant ionic lattice: each ion is surrounded by ions of the opposite charge, and the attractions act in every direction.
| Ion to learn | Formula |
|---|---|
| Sulfate | SO42− |
| Hydroxide | OH− |
| Nitrate | NO3− |
| Carbonate | CO32− |
| Ammonium | NH4+ |
To write a formula, balance the charges: Al3+ and SO42− give Al2(SO4)3.
Check yourself: Write the formula of magnesium nitride.
Mg3N2 (3 × 2+ balances 2 × 3−)
2.2 Covalent and dative bonding
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2.3 Shapes of molecules and ions
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2.4 Electronegativity and polarity
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2.5 Intermolecular forces
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2.6 Explaining physical properties
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2.7 Choosing a solvent
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2.8 Metallic bonding
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2.9 Giant and simple structures
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2.10 Predicting structure and properties
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Extra worked questions
Cover the solution, answer on paper, then mark yourself against each step. Each step shows the mark it earns.
All 8 worked solutions are free for members. The first one is open to everyone.
Bonding in calcium fluoride
Calcium fluoride is an ionic compound. Describe how the ions form and what holds them together in the solid.
Try it first, then show the worked solution
| Electron transfer | Each calcium atom loses two electrons to form Ca2+ | 1 |
|---|---|---|
| Negative ions | Each fluorine atom gains one electron to form F−, so two F− per Ca2+ (CaF2) | 1 |
| Bonding | Strong electrostatic attraction between oppositely charged ions in a giant lattice | 1 |
Answer: Ca → Ca2+ + 2e−; F + e− → F−; ions held by electrostatic attraction in a giant lattice.
Examiner tip: Always say "oppositely charged ions". "Attraction between atoms" or "molecules" scores nothing for ionic bonding.
The ammonium ion
Ammonia reacts with a hydrogen ion to form NH4+. Explain how the new bond forms, and state the shape of the ion.
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Shapes of PCl<sub>3</sub> and XeF<sub>4</sub>
Predict the shape and bond angle of (a) PCl3 and (b) XeF4. Show how you counted the electron pairs.
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Polar and non-polar molecules
Both carbon dioxide and water contain polar bonds. Explain why water is a polar molecule but carbon dioxide is not.
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Water and hydrogen sulfide
Water boils at 100 °C but hydrogen sulfide, H2S, boils at −60 °C, even though H2S has more electrons. Explain this difference.
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Which solvent?
Ethanol mixes completely with water, but 1-chlorobutane does not, even though its C–Cl bond is polar. Explain both observations.
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Sodium, magnesium and aluminium
The melting points of Na, Mg and Al are 98 °C, 650 °C and 660 °C. (a) Explain why melting point rises from Na to Mg. (b) Explain why magnesium conducts electricity.
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Identify the structures
Four solids, W to Z, are tested. W: melts at 1610 °C, insoluble, never conducts. X: melts at 114 °C, does not conduct. Y: melts at 772 °C, conducts when molten but not when solid. Z: melts at 1085 °C, conducts as a solid. Identify the structure of each and explain why Y conducts only when molten.
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Video walkthroughs
Narrated walkthroughs of exam-style questions from this topic of the book, showing where each mark comes from. Try the question first, then watch. Captions are available in the player.
Ionic radii and melting points
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Hydrogen bonding in water and ice
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Identifying structures from their properties
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Recall cards
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