2. Models of the Atom Atomic & Nuclear Physics Lesson 1

3. Homework Revise for the Skills Test next week.

4. Quick Exercise Draw a diagram of a carbon atom, labelling as many parts as you can. Periodic Tables

5. Which is your diagram closest to?

6. Learning Objectives  Describe a model of the atom that features a small nucleus surrounded by electrons.  Outline the evidence that supports a nuclear model of the atom.  Outline one limitation of the simple model of the nuclear atom.

7. Inside the atom… PropertyElectronProtonNeutron Charge -1e +1e 0 Mass 9.11 × 10 -31 kg 1.67 × 10 -27 kg Relative Mass 0.00051.00001.0004 The electron and the proton have the same value of charge, but the signs are different. We also use a quantity for the charge called electronic charge unit, e. 1 e = 1.602 × 10 -19 C. The neutron has almost the same mass as the proton.

8. Question Why don’t the electrons go flying off? Let’s now play with magnets…

9. What happens in each case? S N N S S N S N N S S N

10. Van der Graaf Generator Are we still happy with our model?

11. Challenge - Is it right? Examine the six statements, they are all true. Which of them, if any, support the nuclear model of the atom and why? Do any of the statements present a problem for the nuclear model?

12. Video In Search of Giants (3 of 15) The Discovery of the Atomic Nucleus

13. Size of the nucleus... If the atom were the size of the school canteen, the nucleus would be the size of a pea dropped in the middle. Really small compared to the atom!!

14. For fun?...(don’t worry about the equations) Repulsive force between two protons. Gravitational Attraction. Q 1, Q 2 =e G is gravitational constant. m are proton masses R is distance between the two protons (10 -15 m).

15. Force Comparison Coulomb force of repulsion is about 200N Gravitational Force of attraction is only about 1.9×10 -34 N. So Coulomb force of repulsion is much, much stronger!!

16. What you need to know… Students should be able to describe a simple model involving electrons kept in orbit around the nucleus as a result of the electrostatic attraction between the electrons and the nucleus.

17. What you need to know… A qualitative description of the Geiger–Marsden experiment and an interpretation of the results are all that is required.

18. Recap Describe a model of the atom that features a small nucleus surrounded by electrons. [4 marks]

19. Recap Describe a model of the atom that features a small nucleus surrounded by electrons. [4 marks] A small nucleus (√) consisting of protons and neutrons (√) orbited by electrons (√) of about 1/2000 th mass and an opposite charge (√).

20. Recap Outline the evidence that supports a nuclear model of the atom.

21. Recap Outline the evidence that supports a nuclear model of the atom. [5 marks] Rutherford fired high energy alpha particles (√) at a thin sheet of gold foil (√). The vast majority of particles passed straight through (√) but some of the alpha particles were deflected at large angles (√). This result could only be explained if all the charges of the gold atoms were concentrated at the centre along with mass (√)

22. Recap Outline one limitation of the simple model of the nuclear atom. [2 marks]

23. Recap Outline one limitation of the simple model of the nuclear atom. [2 marks] Either:- The force of repulsion between the positive charges is stronger than the gravitational attraction (√) so the nucleus should fly apart (√). OR:- A particle in an orbit is accelerating and accelerating charges emit radiation (√) so the electron should spiral into the nucleus (√).