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#2

Atomic structure and the periodic table

Paper 1 · Apply

Key steps (method)

  • Write down the particle (proton / neutron / electron) and what you’re being asked to find.
  • Use the periodic table carefully (atomic number = protons; mass number = protons + neutrons).
  • For isotopes, compare mass numbers and keep proton number fixed.
  • For electron structure, fill shells (GCSE model) and relate to groups and periods.

Common mistakes

  • Mixing up atomic number and mass number.
  • Forgetting electrons = protons (for a neutral atom).
  • Writing electron configurations that don’t match the group.

Exam-style questions (quick)

  1. An atom has mass number 35 and atomic number 17. How many protons, neutrons, electrons?
  2. Explain why chlorine has a relative atomic mass of 35.5.
  3. Describe how the structure of the atom changed from Dalton to Rutherford to Bohr.