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How Rutherford Discovered the Nucleus: One of science’s greatest experiments! Rutherford’s Atomic Model Rutherford used the ideas of radioactivity to carry out experiments to help him better define the atomic model. His experiment involved: Exploring matter by shooting radioactive alpha particles against thin sheets of metal. A FEW particles are sharply deflected SEVERAL particles pass through the gold foil & were slightly deflected Alpha Particle beam Thin sheet of Gold foil Radium in Lead Block MOST particles passed through the Fluorescent Screen gold foil & were not deflected Fluorescent Screen MOST went through Alpha Particles empty space Conclusions from Rutherford’s Experiment: FEW approach nucleus & bounced back Gold Atom 3 Main Observations SEVERAL were deflected by the nucleus OBSERVATIONS 1. MOST (almost all) went through the gold foil & were not deflected 2. FEW (not many) bounced directly back 3. SEVERAL (some) passed through the gold foil & were deflected CONCLUSIONS Atom contains a significant amount of empty space The atom’s dense core (nucleus) must be very small The nucleus must be positive (law of repulsion) Rutherford Model Rutherford proposed a new model based on his findings and Thomson's Model. Rutherford’s Model placed electrons orbiting, like a cloud, around a dense, positively charged nucleus. Nucleus Electrons Rutherford’s famous gold foil experiment is shown below. Which of the four statements stated are true and which are false? (there can be more than one true!) Lead Box (Radio active substance ) Gold Lead Florescent Screen 1. Since most of the alpha particles went through the gold foil, the atom consists of mostly of empty space. 2. All of the alpha particles are deflected because they repel the electrons 3. Most of the alpha particles bounce straight back showing that the nucleus is very large. 4. Several of the alpha particles are deflected showing that the nucleus must have a positive charge Rutherford’s Model Be familiar with diagram of experiment Know experiment results: Particles go through - mostly empty space Particles slightly deflected - same charge as nucleus so repelled Particles nucleus bounced back- direct hit on