1. 26/11/2015 The Scattering experiment L/O :- To know the structure of an atom and to understand Rutherford and Marsden’s scattering experiment

2. What does an atom look like? Draw and label a diagram of helium 26/11/2015

3. The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”) Is this what we have always thought? What is this atom mostly made of?

4. 26/11/2015 The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron0 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously)

5. The Ancient Greeks 26/11/2015 The ancient Greeks realised that all matter must be made up of tiny ‘indivisible’ particles. (they figured that you couldn’t just keep chopping something in half forever) So they came up with the idea of the ‘atom’ They also correctly thought that there are lots of types of atom. (periodic table of elements)

6. 26/11/2015 Structure of the atom A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it… I did an experiment (with my colleagues Geiger and Marsden) that proved this idea was wrong. I called it the “Scattering Experiment” Ernest Rutherford, British scientist:

7. Example Question 26/11/2015 How does Rutherford and Marsden’s gold leaf experiment confirm our model of the structure of the atom? (4 marks)

8. 26/11/2015 The Rutherford Scattering Experiment Thin gold foil a few atoms thick Helium Nuclei were fired at a thin gold ‘leaf’. Gold can be rolled out as flat as a few atoms thick. A detector was placed in front and behind the leaf to see how the helium atoms path was affected.

9. 26/11/2015 The Rutherford Scattering Experiment Alpha particles (positive charge, part of helium atom) Thin gold foil Most particles passed through, 1/8000 were deflected by more than 90 0 Conclusion – atom is made up of a small, positively charged nucleus surrounded by electrons orbiting in a “cloud”.

10. 26/11/2015 If the nucleus was not positively charged, what would have happened? Positively charged helium nuclei (alpha particles) are fired at a thin layer of gold leaf. Most of the alpha particles went through, and only a small number deflected back towards the source. This proves that the atom is mostly empty space and that the nucleus is small and positively charged.

11. Question 26/11/2015 How does Rutherford and Marsden’s gold leaf experiment confirm the structure of the atom? (4 marks)

12. Question 26/11/2015 How does Rutherford and Marsden’s gold leaf experiment confirm the structure of the atom? (4 marks) To answer this question we need to say ‘what the current model of the atom is’ and how the experiment proves this. Nuclear model is: Postively charged small nucleus. Most of atom is empty space. How can we write this in full?

13. Question 26/11/2015 How does Rutherford and Marsden’s gold leaf experiment confirm the structure of the atom? (4 marks) It proves that most of the atom is empty space, (1 mark) because most of the helium nuclei went through the leaf un-deflected (2 nd mark) Only a small number of particles were reflected back towards the source. (3 rd mark) The gold nuclei must be positively charged because it repelled the positively charged helium nuclei. (4 marks)

14. Exam question 26/11/2015 Scientists thought that all the parts in atoms were evenly spread. (a)What did scientists expect to happen in this experiment? (2 marks) (b) Complete the sentence. The experiment showed that atoms must be mostly empty....................... (1 mark)

15. 26/11/2015 Explain how Rutherford’s and Marsden’s experiment changed our understanding of atoms

16. 26/11/2015 The structure of the atom ParticleRelative MassRelative Charge Proton1+1 Neutron10 Electron0 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously)

17. 26/11/2015Isotopes An isotope is an atom with a different number of neutrons: Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. Notice that the mass number is different. How many neutrons does each isotope have? A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.