1. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan Rutherfords Gold Foil Experiment T.T.

2. PDST Resources for Leaving Certificate Physics 2 Rutherfords gold-foil experiment The atom is a solid sphere It contains negative electrons Positive material Negative electrons This was called the Plum Pudding Model Before this experiment, we assumed that: Electrons were compared to fruit, positive material to cake

3. PDST Resources for Leaving Certificate Physics 3 97 % 2 - 3 % <1 % Ra Rutherford fired α-particles at gold foil He knew α-particles were small, fast moving and positive 97% went straight through 2-3% were deflected Less than 1% bounced back LiS movable Lithium sulphide detector Rutherfords gold-foil experiment

4. PDST Resources for Leaving Certificate Physics 4 97 % 2 - 3 % <1 % Ra LiS movable Lithium sulphide detector The key result is the 1% that bounce back Rutherford compared the experiment to firing artillery shells at tissue paper Why would any bounce back? Rutherfords gold-foil experiment

5. PDST Resources for Leaving Certificate Physics 5 + + He concluded that: 97% pass through because they are meeting nothing Those deflected are coming close to a positive charge Those that bounce back are heading straight for a positive charge 97% 2-3% 1% The atom is mainly empty space, with a small area of positive charge Rutherfords gold-foil experiment

6. PDST Resources for Leaving Certificate Physics 6 Conclusions The atom is mainly empty space There is a small area of positive charge at the centre (the nucleus) + nucleus electrons The Rutherford – Bohr Model of the Atom (as studied at junior cert.)

7. PDST Resources for Leaving Certificate Physics 7 Atomic number The number of protons Mass number The total number of protons and neutrons All elements have an atomic and mass number e.g. for Lithium: 3p 4n