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S4 Chemistry: Periodic Table Paper 4 (Error Redo)
S4 Chemistry: Periodic Table Paper 4 (Error Redo)
This paper reworks the marks lost in papers 1 to 3: the atomic number of anions, mass number against neutrons, reading period and group, isoelectronic radii and molar mass.
Quick answer Four foundation items on atomic number, neutrons, period and relative molecular mass; three intermediate items on molar mass, isoelectronic ion radii and ionic compounds; two challenge items on noble gases and mass fraction; then one item correcting three errors at once.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 20 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Chemistry – Periodic Table |
| Level | Error redo |
02 Questions (10 items)
- FoundationAn ion X2- contains 18 electrons. What is the atomic number of X?
- FoundationA potassium atom has mass number 39 and 20 neutrons. Give its atomic number and electron count.
- FoundationCopper has the arrangement 2, 8, 18, 1. Which period is it in and what type of element is it?
- FoundationWhat is the relative molecular mass of water (H 1, O 16) and what does 1 mol weigh?
- IntermediateWhat is the mass of 0.5 mol of magnesium (Mg 24), and how many atoms does it hold (L = 6.02×10^23 /mol)?
- IntermediateNa+ 102 pm, Mg2+ 72 pm and Al3+ 54 pm all hold 10 electrons. Order them from largest down and explain.
- IntermediatePotassium (2, 8, 8, 1) reacts with chlorine (2, 8, 7). Give the ion formulas and the relative formula mass (K 39, Cl 35.5).
- ChallengeElement Y has the arrangement 2, 8, 18, 18, 8. Give its atomic number, period and group, and say whether it is reactive.
- ChallengeHow much magnesium is there in 20 g of magnesium oxide (Mg 24, O 16)?
- Error redoA student wrote: chlorine has atomic number 17, so its mass number is 17, it has 17 neutrons and it sits in group 17. What is wrong three times?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Atomic number 16 | The anion gained two electrons, so take two off to get the atomic number. |
| 2 | Atomic number 19; 19 electrons | Protons equal mass number minus neutrons, 39 – 20 = 19, and a neutral atom has as many electrons. |
| 3 | Period 4; a transition metal | The number of shells gives the period (four shells means period 4); one outer electron means a metal. |
| 4 | 18; 1 mol weighs 18 g | Relative molecular mass is 2×1 + 16 = 18, which equals a molar mass of 18 g/mol. |
| 5 | 12 g; 3.01×10^23 atoms | Mass = 0.5 x 24 = 12 g; particles = 0.5 x 6.02×10^23 = 3.01×10^23. |
| 6 | Na+ then Mg2+ then Al3+, largest first; with equal electrons, more protons means a smaller ion | Proton counts are 11, 12 and 13, so the nuclear pull rises and the radius falls. |
| 7 | K+ and Cl-; KCl has relative formula mass 74.5 | Potassium loses one electron and chlorine gains one; 39 + 35.5 = 74.5. |
| 8 | Atomic number 54; period 5, group 0; unreactive | Total electrons 54; a full outer shell of eight makes it a noble gas, chemically stable. |
| 9 | 12 g | MgO has relative formula mass 40; magnesium is 24/40, six tenths, so 20 x 0.6 = 12 g. |
| 10 | Mass number 35, 18 neutrons, group VII with seven outer electrons | The atomic number only counts protons; neutrons come from mass number minus protons; the group comes from outer electrons. |
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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