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S4 Chemistry: Periodic Table and Trends Paper 2 (Atomic Radius, Ionisation Energy and Reactivity)
S4 Chemistry: Periodic Table and Trends Paper 2 (Atomic Radius, Ionisation Energy and Reactivity)
This paper uses supplied data to compare radii and first ionisation energies, explains the aluminium dip and the fall down a group, and ranks metallic character from ionisation energies.
Quick answer 1. 186 > 160 > 143 > 118 | 2. 152 < 186 < 227 | 3. rises, noble gas highest | 4. one more proton, smaller radius | 5. 3p is higher and shielded | 6. it falls | 7. K 419 < Li 520 | 8. fluorine | 9. K > Na > Li | 10. Na+ is smaller than Na and Cl- is larger than Cl
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Chemistry – Periodic Table and Trends |
| Level | Application |
02 Questions (10 items)
- FoundationAtomic radii in pm: Na 186, Mg 160, Al 143, Si 118. How does radius change across the period?
- FoundationRadii in pm: Li 152, Na 186, K 227. How does radius change down the group?
- FoundationAcross a period, how does first ionisation energy change, and which element is highest?
- FoundationWhy is the first ionisation energy of magnesium (736 kJ/mol) higher than that of sodium (494 kJ/mol)?
- IntermediateAluminium first ionisation energy (577 kJ/mol) is lower than magnesium (736). Why?
- IntermediateWhat is the trend in first ionisation energy down a group? Explain with radius.
- IntermediateStrong metallic character means losing electrons easily. Which is more metallic, potassium or lithium?
- ChallengeAmong fluorine, chlorine and bromine, which is the most non-metallic and why?
- ChallengeRank potassium, sodium and lithium by how violently they react with water.
- Error redoA student claimed the sodium ion is larger than the sodium atom and the chloride ion smaller than the chlorine atom. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | It decreases: 186 > 160 > 143 > 118 pm | Nuclear charge grows while the shell count stays the same, pulling electrons closer. |
| 2 | It increases: 152 < 186 < 227 pm | Each step down adds a shell, so the atom gets bigger. |
| 3 | It rises overall; the noble gas of that period (neon, argon) is highest | Smaller radius and stronger attraction mean more energy to remove an electron. |
| 4 | Magnesium has one more proton and a smaller radius, so its outer electron is held more strongly | Within a period, nuclear charge is the dominant factor. |
| 5 | The outer 3p electron of aluminium is higher in energy and shielded by the 3s pair, so it leaves more easily | The small dip within a period comes from the 3p versus 3s difference. |
| 6 | It falls; the radius grows, so the outer electron is farther out and better shielded | K 419 < Na 494 < Li 520, which matches the trend. |
| 7 | Potassium; its first ionisation energy of 419 kJ/mol is below lithium 520 | The lower the ionisation energy, the easier the electron loss, so the stronger the metal. |
| 8 | Fluorine; it has the smallest radius and strongest pull, so it gains electrons most readily | Non-metallic character increases upwards, the opposite of metallic character. |
| 9 | Potassium > sodium > lithium | Metallic character increases down the group, so the reaction gets more violent. |
| 10 | The reverse: Na+ (102 pm) is smaller than Na, while Cl- is larger than Cl | A cation loses its outer shell and shrinks; an anion gains electrons, repulsion swells it. |
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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