1. A history of atomic structure
AH Chemistry, Unit 1(a)

2. The key players: part 1 John Dalton J..J. Thompson Eugene Goldstein
Max Planck
Proposed atomic theory
Discovered the electron
Discovered the proton
Quantization of energy
1808
1897
1900
1900
Albert Einstein
Ernst Rutherford
Niels Bohr
James Chadwick
Photoelectric effect
Discovered the nucleus
Devised the quantum model
Discovered the neutron
1905
1911
1913
1932

3. One of the best ways of probing the structure of an atom is by studying their interaction of electromagnetic radiation.

4. Electromagnetic spectrum

5. Wave structure

6. Heating objects What colour do objects turn when they are heated? Red
Orange
Yellow
White
Blue

8. Quantisation
In 1900, Max Planck proposed that electromagnetic radiation could only be emitted or absorbed in small packets (quanta).
These were later called photons.

9. The photoelectric effect
UV radiation
No electrons emitted until a particular frequency is reached (threshold) which is specific to the metal
The higher the intensity, the more electrons that are ejected

10. Why does it happen? UV radiation
No electrons emitted until a particular frequency is reached (threshold) which is specific to the metal
The higher the intensity, the more electrons that are ejected

11. Energy of photons Proportional to their frequency
E = hv (for a single photon)
E = Lhv (for one mole of photons)

12. SQA 2009 paper

13. So light is made up of particles?
Only when we want it to be!

14. The single slit experiment: light

16. Diffraction

17. The double slit experiment: light

22. Here, the evidence is that light is behaving as waves.
Light has wave-particle duality.

23. What about if you do it with electrons?

24. This does not happen!

26. Light and electrons both have dual wave-particle properties.
The electrons appear to be behaving as waves and producing an interference pattern.
In 1906, J.J. Thompson won the Nobel Prize for showing that electrons were particles.
In 1937, G.P. Thompson (his son) won the Nobel Prize for showing that electrons where waves.
Light and electrons both have dual wave-particle properties.
Does anything else?

27. Everything!
It’s just that to appreciate wave properties, you have to be in the realms of the very, very small

28. What about if only one electron is fired at a time, so there can be no interference?

31. …but this does not happen if only one slit it present!

32. A possible explanation is that the electron splits when it is fired at a double slit, one part passing through one slit and one part passing through the other.
But how did the electron know that the other slit was there?

33. If it does split, behaving as waves, this would allow for the constructive and destructive interference observed.
This theory can be tested further using particle detectors…

34. Particle detectors

35. What happens?
Only one green detector ever registers an electron at any one time, never both simultaneously.
None of the pink detectors detect an electron.
The electron has stopped behaving as a wave when the particle detectors are introduced!

36. The paradox
With no particle detectors, it seems to go through both and behave as a wave; with particle detectors to goes through one and behaves as a particle.
Knowledge of the detectors seems to be influencing the event.
Where has this knowledge come from?
The only place it can have come from is the mind of the observer.

37. In other words, simply by observing, the observer influences the outcome.

39. Explore it further…