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S4 Chemistry: Chemical Bonding and Structure (Paper 4)
S4 Chemistry: Chemical Bonding and Structure (Paper 4)
The fourth paper stresses error repair and mixed application: ion ratios, lone pairs, melting points of giant structures and the conditions for conduction.
Direct answer Separate ionic bonding, which involves ions, from covalent bonding, which shares electron pairs; compare melting points and hardness by structure type, not by bond type alone.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Chemistry: Chemical Bonding and Structure |
| Level | Four basic, three advanced, two challenge and one error-repair item |
02 Questions (10 items)
- FoundationIn sodium chloride, what force holds the sodium ion and the chloride ion together?
- FoundationMagnesium has atomic number 12 and chlorine 17. In the compound they form, what is the ratio of magnesium ions to chloride ions?
- FoundationAt the simplest level, how do two atoms join in a covalent bond?
- FoundationWhat feature of graphite lets it conduct electricity?
- IntermediateWhy does solid sodium chloride not conduct electricity while the molten salt does?
- IntermediateDiamond and graphite are both carbon. Why is diamond extremely hard while graphite is soft?
- IntermediateIn an ionic compound XCl₂ the X ion carries a +2 charge. How many moles of chloride ions come from 0.10 mol of XCl₂?
- ChallengeIn a water molecule the oxygen atom (atomic number 8) bonds to two hydrogens. How many lone pairs remain on oxygen?
- ChallengeSilicon dioxide melts near 1 710 °C, far above the 801 °C of sodium chloride. What type of structure is SiO₂?
- Error redoA student says diamond is soft because the carbon atoms are only weakly attracted. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Electrostatic attraction, that is an ionic bond | The metal loses electrons to form a cation and the non-metal gains them to form an anion; the electrostatic attraction between them is the ionic bond. |
| 2 | 1 : 2, giving MgCl₂ | Magnesium loses two electrons to become Mg²⁺ while each chlorine gains one to become Cl⁻, so two chloride ions balance one magnesium ion. |
| 3 | They share one pair of electrons | Two non-metal atoms each contribute one electron to a shared pair, so both reach a more stable arrangement. |
| 4 | Each carbon has one delocalised electron that can move within the layer | Each carbon in a graphite layer forms three covalent bonds and its fourth electron is delocalised, so current flows along the layer. |
| 5 | In the solid the ions are locked in the lattice; when molten they can move freely | Conduction needs mobile charged particles: in the solid the ions only vibrate, but once melted the lattice breaks up and the ions move freely. |
| 6 | Diamond is a three-dimensional covalent network; graphite layers are held by weak forces between them | Every carbon in diamond is covalently bonded to four others in a three-dimensional network, while graphite layers slide because the forces between them are weak. |
| 7 | 0.20 mol | Each formula unit contains two chloride ions, so 0.10 times 2 gives 0.20 mol; charge balance confirms +2 against two minus ones. |
| 8 | Two lone pairs | Oxygen has six valence electrons; two are shared with hydrogen, leaving four electrons, that is two lone pairs, which bend the molecule. |
| 9 | A giant covalent, or atomic, structure | Each silicon in SiO₂ is covalently bonded to four oxygens in a three-dimensional network, so melting demands breaking many covalent bonds. |
| 10 | Diamond is a three-dimensional covalent network of strong bonds, which makes it the hardest form of carbon | The weak forces between graphite layers were wrongly transferred to diamond, where every carbon is bonded to four others in a rigid network. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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