A complete revision and exam practice pack for SC3a Structure of an Atom, covering the full Pearson Edexcel GCSE Chemistry (9–1) Separate Science specification for this topic (C1.1–C1.5).

Topic Mastery Sheet (PDF) - a comprehensive student reference that traces the development of atomic models from Dalton’s solid sphere through Thomson’s plum pudding model to Rutherford’s nuclear model and Bohr’s shell model. Each model is described with the evidence that supported it and the new evidence that forced a revision. Rutherford’s gold foil experiment is explained in full: alpha particles directed at thin gold foil mostly passed straight through (confirming the atom is mostly empty space), but a small number deflected at large angles and a very few bounced back (revealing a tiny, dense, positive nucleus). The subatomic particle table gives the relative mass, relative charge and location of protons, neutrons and electrons. The scale comparison shows just how small the nucleus is - if scaled to a marble, the atom would be a kilometre across. The explanation of why atoms are electrically neutral builds from first principles: equal numbers of protons (+1) and electrons (−1) means the charges cancel exactly. The stretch section covers the discovery of the neutron by Chadwick in 1932 and why it took so much longer to find than the electron and proton.

Student Exam Practice Sheet (PDF + DOCX) - six exam-style questions including neutron properties MCQ, nucleus size statement, two-model comparison, electrical neutrality explanation, a four-mark carbon atom diagram, and a three-part question on two atoms with the same mass number but different atomic numbers.

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

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