A complete revision and exam practice pack for SC3c Isotopes, covering the full Pearson Edexcel GCSE Chemistry (9–1) Separate Science specification for this topic (C1.9–C1.12).

Topic Mastery Sheet (PDF) - a comprehensive student reference that defines isotopes as atoms of the same element with the same proton number but different neutron numbers, using a chlorine-35/chlorine-37 comparison table to make the concept concrete. The section on why isotopes have the same chemical properties connects to electronic configuration: identical proton numbers mean identical electron numbers, identical electron arrangements, and therefore identical chemical behaviour - the extra neutrons in heavier isotopes contribute nothing to chemistry. The relative atomic mass section explains clearly why RAM is not a whole number: it is a weighted average across all naturally occurring isotopes, pulled between their masses according to their relative abundances. Three fully worked RAM calculations are included - copper (69% Cu-63, 31% Cu-65, RAM = 63.62), chlorine (75% Cl-35, 25% Cl-37, RAM = 35.5), and boron working backwards from RAM = 10.8 to estimate the percentage abundances (80% B-11, 20% B-10). The stretch section covers radioactive isotopes including carbon-14 dating, iodine-131 in cancer treatment, and why the tellurium/iodine anomaly in Mendeleev’s table is explained by isotope abundance.

Student Exam Practice Sheet (PDF + DOCX) - five exam-style questions covering isotope definition, the effect of chlorine’s isotopes on its RAM, why isotopes have similar chemical properties, the copper RAM calculation to 2 d.p. (Higher tier), and the boron abundance estimation (Higher tier).

Teacher Answer Key (PDF + DOCX) - full tick-point mark scheme with examiner notes.

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