Describe how scientists' understanding of atomic structure changed from Dalton's model to Rutherford's nuclear model, including the experimental evidence that led to this change.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Our understanding of atomic structure has developed over time as new experimental evidence became available. Scientists including Dalton, Thomson, and Rutherford each proposed different models of the atom.
Model answer (4 marks)
Dalton’s model (1803) described the atom as a solid, indivisible sphere that could not be divided or split.
Thomson’s (1897) plum‑pudding model proposed that the atom was a positively charged sphere with negatively charged electrons embedded throughout it.
Geiger and Marsden’s (1909) gold‑foil experiment fired alpha particles at a thin gold foil; most particles passed straight through, but a small number were deflected at large angles, even backwards.
Rutherford (1911) interpreted this result as evidence that the atom contains a tiny, dense, positively charged nucleus surrounded by mostly empty space in which the electrons orbit.
Thomson’s (1897) plum‑pudding model proposed that the atom was a positively charged sphere with negatively charged electrons embedded throughout it.
Geiger and Marsden’s (1909) gold‑foil experiment fired alpha particles at a thin gold foil; most particles passed straight through, but a small number were deflected at large angles, even backwards.
Rutherford (1911) interpreted this result as evidence that the atom contains a tiny, dense, positively charged nucleus surrounded by mostly empty space in which the electrons orbit.
Examiner tips
- Use the exact terminology (solid sphere, plum‑pudding, gold‑foil, nucleus).
- Show the logical progression: Dalton → Thomson → experiment → Rutherford.
- Keep each point brief and to the point.
Mark scheme (4 marks)
- Dalton described atoms as solid spheres that could not be divided / split
- Thomson's plum pudding model proposed the atom was a positively charged sphere with negatively charged electrons embedded in it / dotted through it
- Geiger and Marsden fired alpha particles at a thin gold foil and found most passed straight through but some were deflected more than expected / back
- Rutherford concluded the atom has a small, positively charged nucleus surrounded by mostly empty space with electrons orbiting it
Key terms in this question
atomic structure · nuclear model
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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