Rutherford's Gold Foil Experiment
Discover how Ernest Rutherford's famous experiment revolutionized our understanding of atomic structure and led to the discovery of the atomic nucleus.
Key Discovery:
The atom consists mostly of empty space with a tiny, dense nucleus containing most of the atom's mass and all of its positive charge.
Historical Context
Thomson's Plum Pudding Model
After J.J. Thomson discovered the electron, he proposed the "plum pudding model" of the atom. This model described the atom as a structure with positive charge spread uniformly throughout, with negatively charged electrons embedded within it like raisins in a pudding.
The Experiment (1911)
In 1911, Ernest Rutherford and his students Hans Geiger and Ernest Marsden performed an experiment to test Thomson's model. They directed a beam of positively charged alpha particles at a thin gold foil and observed their behavior using scintillation screens.
Expected vs. Observed Results
According to Thomson's model, the positive charge was spread throughout the atom, so alpha particles should have passed through with minimal deflection. However, while most particles did pass through unaffected, some were deflected at very large angles—some even bounced nearly straight back!
Interactive Simulation
Compare the expected behavior according to Thomson's model with the actual observed results that led to Rutherford's revolutionary discovery.
Click the buttons below to see the difference between expected behavior (Thomson model) and the actual experimental results that led to Rutherford's discovery.
Experimental Setup
Atomic Model
Select a behavior mode to see the atomic model
Rutherford's Nuclear Model
The Revolutionary Conclusion
To explain the experimental results, Rutherford proposed that the positive charge of the atom was concentrated in a tiny region of space—the nucleus. This nucleus was incredibly small relative to the size of the atom but contained nearly 99% of the atom's mass.
The Planetary Model
Rutherford suggested that electrons orbited around the nucleus much like planets orbit the sun. This explained why most alpha particles passed through undeflected (the atom is mostly empty space) while some were deflected at large angles (they encountered the dense, positively charged nucleus).
Key Insights:
- • The atom is mostly empty space
- • The nucleus is extremely small but contains most of the atom's mass
- • All positive charge is concentrated in the nucleus
- • Electrons exist in the space around the nucleus
Impact and Legacy
Rutherford's model laid the foundation for our modern understanding of atomic structure. While later refined by quantum mechanics, the concept of a dense nucleus surrounded by electrons remains central to atomic theory. This experiment demonstrated the power of particle physics and paved the way for nuclear physics and quantum mechanics.