1. How Rutherford Discovered the Nucleus: One of science’s greatest experiments!

2.  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. Rutherford’s Atomic Model

3. Radium in Lead Block Alpha Particle beam Fluorescent Screen Thin sheet of Gold foil Fluorescent Screen A FEW particles are sharply deflected MOST particles passed through the gold foil & were not deflected SEVERAL particles pass through the gold foil & were slightly deflected

4. Conclusions from Rutherford’s Experiment: 3 Main Observations OBSERVATIONSCONCLUSIONS 1. MOST (almost all) went through the gold foil & were not deflected Atom contains a significant amount of empty space 2. FEW (not many) bounced directly back The atom’s dense core (nucleus) must be very small 3. SEVERAL (some) passed through the gold foil & were deflected The nucleus must be positive (law of repulsion) Alpha Particles MOST went through empty space FEW approach nucleus & bounced back SEVERAL were deflected by the nucleus Gold Atom

5. 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. Electrons Nucleus

6. 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 Gold Florescent Screen Lead Box (Radio active substance ) 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

7.  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 bounced back- direct hit on nucleus