In 1909, scientists working with Rutherford fired alpha particles at a very thin sheet of gold foil. Alpha particles are small, positively charged particles. At the time, most scientists accepted the plum pudding model of the atom.
The table shows typical results.
| Observation | Number of alpha particles |
|---|---|
| passed straight through with little or no deflection | 79 950 |
| deflected through a small angle | 40 |
| bounced back towards the source | 10 |
| total fired | 80 000 |
State what the plum pudding model predicted would happen to all the alpha particles.
Calculate the percentage of alpha particles that passed straight through. Give your answer to two decimal places.
Explain what the results show about the structure of the gold atom.
Most alpha particles passed straight through.
A very small number of alpha particles bounced back.
The diameter of a gold atom is about 0.30 nm, where 1 nm = 1 × 10-9 m. The diameter of a gold nucleus is about 1.5 × 10-14 m. Calculate how many times larger the diameter of the atom is than the diameter of the nucleus. Give your answer in standard form.
The experiment is repeated with gold foil that is half as thick. Predict how the number of alpha particles that bounce back will change. Give a reason.
46 exam-style questions on Edexcel GCSE Chemistry 2.1 Atomic structure, covering 2.1.1 Development of the atomic model, 2.1.2 Structure of the atom and subatomic particles, 2.1.3 Mass number, isotopes and relative atomic mass, and 2.1.4 Calculating relative atomic mass from isotopic abundance. Each one has a worked solution and a mark scheme showing where the marks go.