Explain how the results of the alpha particle scattering experiment led scientists to conclude that atoms contain a nucleus.

Edexcel GCSE Chemistry (1CH0) — 1.3 Atomic structure · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

In the early 1900s, Ernest Rutherford and his colleagues fired positively charged alpha particles at a thin sheet of gold foil and observed where the particles went after hitting the foil. Most passed straight through, some were deflected at small angles, and a very small number bounced back almost the way they came.

Model answer (4 marks)

Most alpha particles passed straight through the foil, showing that the atom is largely empty space.
Some particles were deflected at small angles, proving that a small, positively charged centre exists.
A very small number were scattered back almost directly, indicating that this centre is very small in size.
The fact that the scattering occurs in a tiny region shows that the nucleus contains most of the atom’s mass and is dense.

Examiner tips

Use the exact phrases from the mark scheme – ‘empty space’, ‘positively charged’, ‘very small’, ‘most of the mass’. Show the logical sequence: passage → deflection → back‑scatter. Keep each point short and to the point, matching the four marks.

Common mistakes

Mixing up the order of the points or omitting one of the four key observations. Using vague terms such as ‘big centre’ instead of ‘small nucleus’ or ‘dense’.

Mark scheme (4 marks)

Most alpha particles passed straight through, showing that most of the atom is empty space
Some alpha particles were deflected / changed direction, showing the nucleus is positively charged
A very small number bounced back / were deflected through large angles, showing the nucleus is very small
The nucleus contains most of the mass of the atom / the nucleus is dense

Key terms in this question

alpha particle scattering experiment · nucleus