Rutherford’s gold foil experiment
Ernest Rutherford, along with Hans Geiger and Ernest Marsden, carried out the gold foil experiment to understand the structure of an atom and postulated Rutherford’s atomic model.
Gold Foil Experiment
In this experiment, the path of alpha particles was traced as they were made to hit the atoms of a gold foil. Alpha particles are doubly charged helium ions with a mass of about four times that of a hydrogen atom.
Gold Foil Experiment Setup
Rutherford used a source of alpha particles, locked in a lead container with a small slit. This ensured that the alpha particles only came out through a small opening and traveled in a straight line. The gold foil used in this experiment was very thin, having a thickness of approximately 1000 atoms.
Gold Foil
Alpha particles were selected because of their greater mass and energy compared to protons. To trace the track of alpha particles, a circular band of fluorescent screen with a gap was used. The screen would glow or emit fluorescent light whenever hit with the alpha particles.
Alpha Particles Passing Through Atoms
As per Thomson’s plum pudding model, all alpha particles were expected to pass right through the atoms and hit the detector straight.
However, the observations made by Rutherford were different than the ones theorised:
- Most of the fast-moving alpha particles passed straight through the foil and hit the detector.
- Some particles got deflected by small angles
- Very few alpha particles
Observations of gold foil experiment
These observations made Rutherford think that the plum pudding model is incorrect and led to
the formation of Rutherford’s atomic model.