Rutherfords Model of the Atom

1




2





3
Rutherfords Model of the Atom

• Most of the atom is empty space.
• Most of the atoms mass and charge is located
  at the center of the atom.

4
Next

• Bohrs model
• How a laser works
• X-ray production
• Wave-particle duality
• Quantum Physics

5
Exercise

• A radiostation broadcasts at 89.3 MHz with a
  radiated power of 43.0 kW.
• What is the magnitude of the momentum of each
  photon?
• How many photons does the radiostation emit each
  second?

6
Exercise

• For a certain cathode material in a
  photoelectric-effect experiment you measure a
  stopping potential of 1.0V for light for
  wavelength 600nm, 2.0 V for 400 nm, and 300nm for
  300nm. Determine the work function for this
  material and the value of Plancks constant.

7
Emission spectral
8
Things to consider

• Unique spectral lines for each element.
• Each spectral line has a particular frequency gt
  particular photon energy
• Heavy positively charge nucleus in the center of
  the atom arounded by electrons.

9

• Attraction between negative electrons and
  positived nucleus.
• Rutherfords proposal

-
-

-
-
-
10
Bohrs model

• Electrons move around the nucleus at stable
  orbits without emitting radiation.
• Electron in one of these stable orbit has a
  definite energy.
• Energy is radiated only when electrons make
  transitions from high energy orbit to a low
  energy orbit.

11
hf

12
hf

13

• Energy is emitted as photons with energy

-
-
14
Quantifying the energy spectrum

• Bohr postulate that the angular momentum of an
  electron revolving around a nucleus is quantized
  in units of h/2p

15

• Newtons 2nd law yields

16

• The smallest radius is obtained by setting n 1,
  is called the bohr radius.

17

• Kinetic energy of moving electrons

18

• Potential energy of electron bound to nucleus

19
Total energy of electron n-th orbital
20
Energy level diagram

• The possible energies which electrons in the atom
  can have is depicted in an energy level diagram.

21
Bohrs model and the operation of the Laser

• In 1958, Charles Townes and Arthur Schawlow
  theorized about a visible laser, an invention
  that would use infrared and/or visible spectrum
  light.
• Light Amplification by Stimulated Emission of
  Radiation- (LASER).
• Properties of Lasers
• Produce monochromatic light of extremely high
  intensity.

22
Bohrs model and the operation of the Laser
23
Bohrs model and the operation of the Laser
(Pumping the Laser)
24
Bohrs model and the operation of the Laser
25
Bohrs model and the operation of the Laser
26
Bohrs model and the operation of the Laser
27
Bohrs model and the operation of the Laser
28
Bohrs model and the operation of the Laser
29
Bohrs model and the operation of the Laser
30
Bohrs model and the operation of the Laser
31
Bohrs model and the operation of the Laser
32
X-ray production

• Properties of x-rays.
• High penetration gt High energy gtHigh frequency.
• X-rays are produced when acelerated electrons
  strike a heavy metalic target (W).

33
Operation of an X-ray machine
34
X-ray production on the atomic scale
35
X-ray production on the atomic scale
36
ALLAN MACLEOD CORMACK 1924-1998

• Lecturer in Physics, University of Cape Town,
  1950 - 1957
• Nobel Prize for Physiology and Medicine, 1979
• Development of the CAT scanner (Computer Aided
  Tomography).

37
SIR AARON KLUG

• MSc student in Physics, University of Cape Town,
  1946? - 1948
• Nobel Prize for Chemistry 1982
• Probing the properties of macromolecules (DNA)
  with x-rays.

38
Wave-Particle Duality

• In the Bohr model, electrons orbit the atomic
  nucleus in stable orbits.
• What makes an orbit stable?
• Louis de Broglie proposed that subatomic
  particles, such as electron, could exhibit some
  wave behaviour.

39
De Broglies Wave Particle Model

• Similar to photons

• Wavelength of particle is related to its momentum
  by

40

• where

41
Bohrs model with wavy electrons

• An electron orbit is stable if an integer number
  of de Broglie standing wave can fit into it.

42

• General

43

• Yields

44
Wave Phenomenon

• Phenomenon associated with waves include
• Interference effects
• Reflection
• Refraction

45
Interference

• Superposition of wave pulse

46
Davidson-Germer experiment

• Aim to test if particle (electrons) exhibit
  properties of waves i.e. Inteference.
• Youngs experiment to find interference pattern
  due to particle wave interaction.

47
?
48
Electron diffraction pattern
49
Scanning electron microscope images
50
(No Transcript)
51
Theory of Quantum mechanics

• Understanding the nature of the particle waves.
• Heisenbergs uncertainty principle
• Schroedingers equation.
• Spin-off of quantum theory in the todays world

52
Quantum Scale
53
Heisenbergs Uncertainty Principle

• On the scale on life size object a system is not
  influenced by measurements on a system
  (Deterministic system).
• On the atomic scale a measurement on a system
  will influence on it.

54
Finding the location of an electron
-
55
Finding the location of an electron
-
56
The Uncertainty Principle

• Act of measurement influences the electrons
  state
• Neither the position nor the momentum of a
  particle can be determined with arbitrary great
  precision

57
Schroedingers Wave Equation
58

• Heisenberg Uncertainty de Broglie waves
  Schroedingers probabily waves function

59
Schroedingers solution to the electron orbitals
in the atom