E.1.1—Rutherford experiment
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- HL
Interpret Rutherford Scattering
Set up the evidence
In the Geiger–Marsden–Rutherford experiment, alpha particles were directed at a thin gold foil and detected around the foil. Most particles passed through without deflection, some were deflected, and a very small number scattered backwards.
Infer the nuclear model
The results show that an atom is mostly empty space. The rare large deflections require a small, dense, positively charged nucleus that contains most of the atom’s mass; the positive charge cannot be spread uniformly through the whole atom.
Keep the conclusion qualitative
For SL, focus on linking each observation to the model: many undeflected particles imply empty space, while rare back-scattering implies a concentrated repulsive centre. Do not treat the experiment as evidence that electrons occupy fixed-radius orbits.
Common trap
Do not say that all alpha particles are deflected. The dominant observation is that most pass through essentially undeflected; the large-angle events are rare but decisive.
E.1.1 Exam Analysis
Assessment in practice
1–2 marksHow it is assessed
Questions ask learners to identify which atomic claim is falsified or to describe observations of the experiment.
Command terms
Describe / Identify
What earns marks
Name the observations precisely: most alpha particles pass through undeflected, some are deviated, and a few bounce back. Then connect them to the nuclear model when an inference is requested.
Watch for
Saying that positive charge fills the entire atom or omitting the observation that most alpha particles pass through undeflected.
Retrieve the SL Atomic Model
Retrieve the evidence chain
Rutherford scattering supports a small positive nucleus; nuclear notation separates protons, neutrons and electrons; line spectra show discrete energy differences; and Eγ=hf=hc/λ connects transitions to photons.
Check the model
When reading a spectrum, identify the transition, use the energy difference rather than an absolute level, and compare characteristic lines with known spectra to identify elements.