IGCSE Chemistry Paper 2 & 3
Topic 2.2.2: Atomic Structure Calculations
Exam Instructions
- • Answer ALL questions in the spaces provided
- • Show ALL working for calculation questions
- • Write your answer first, then click "Reveal Answer" to check
- • Compare your answer with the mark scheme carefully
ASection A: Definitions
Define key atomic structure terms
1. Define the term "Proton Number" (Atomic Number).
2. Define the term "Nucleon Number" (Mass Number).
3. State what is meant by "isotopes".
4. Define an "ion".
5. State the relative charges and masses of a proton, neutron, and electron.
BSection B: Atomic Calculations
Calculate protons, neutrons, and electrons in atoms
6. An atom has a Proton Number of 9 and a Nucleon Number of 19. Calculate the number of neutrons in this atom.
7. Calculate the number of protons, electrons, and neutrons in an atom of ³⁷Cl (Chlorine-37). The proton number of chlorine is 17.
8. An atom of magnesium has 12 protons and 12 neutrons. State its nucleon number and write it in standard notation (²⁴₁₂Mg format).
9. Carbon-14 (¹⁴C) is used in radioactive dating. If carbon has a proton number of 6, how many neutrons does Carbon-14 contain?
10. An atom of element X has 20 protons and 20 neutrons. Another atom of element X has 20 protons and 22 neutrons. Explain why these are isotopes and write both in standard notation.
CSection C: Ion Mathematics
Master electron changes in ion formation
11. How many electrons are present in an O²⁻ ion? (Oxygen has a proton number of 8)
12. A sodium atom (Na) has 11 protons and 11 electrons. Calculate the number of electrons in a Na⁺ ion.
13. An Al³⁺ ion has 10 electrons. Calculate the number of protons and neutrons if the nucleon number is 27.
14. A chloride ion (Cl⁻) has 18 electrons. State the number of protons in this ion and explain your reasoning.
15. Complete the table below for the following particles: | Particle | Protons | Electrons | Neutrons | |----------|---------|-----------|----------| | ²⁴₁₂Mg²⁺ | ? | ? | ? | | ³⁵₁₇Cl⁻ | ? | ? | ? |
Examiner Tips 🎯
•Nucleon Number - Proton Number = Neutrons (Most common calculation)
•Positive ions LOSE electrons: Na⁺ has 10e⁻ (not 11)
•Negative ions GAIN electrons: O²⁻ has 10e⁻ (not 8)
•Always show your working - you can get marks even if final answer is wrong
•Isotopes: Same protons, different neutrons (e.g., ¹²C and ¹⁴C)
Common Exam Mistakes to Avoid
✗Confusing mass number with atomic number
✗Forgetting that ions have DIFFERENT electron numbers than neutral atoms
✗Writing "electrons in nucleus" (electrons orbit the nucleus!)
✗Not showing working in calculation questions
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