Day 2.5
A Quantum Model of the Atom
1) Two hundred years ago Dalton suggested that matter was made of atoms – indivisible particles whose
mass differs from element to another. Physicists have changed that model a great deal.
a) Just over 100 years ago J.J. Thompson proposed a plum pudding model. How was it different from
Dalton’s model? Make a labelled sketch of it. What was the experimental evidence for it?
b) In 1911 Rutherford proposed a solar system model. How was it different from Thompson’s model?
Make a labelled sketch of it. What was the experimental evidence for it?
Modelling Rutherford’s Model:
2) In Rutherford’s model the electron is orbiting the nucleus, like a satellite orbiting the Earth. This can
be modelled with a ball rolling on a curved surface. In this model the balls/electrons are
A) not accelerating because the speed is constant
B) not accelerating because there is no net force
C) accelerating because the velocity is changing direction and there is a net force toward the centre
D) accelerating because the velocity is changing direction and there is a net force away from the centre
3) The balls in this model lose energy and spiral in but the electrons in an atom do not because there is
a) no air resistance and no friction
B) no air resistance and negligible friction
C) negligible air resistance and no friction
D) negligible air resistance and negligible friction
Rutherford’s First Problem:
4) Go to http://phet.colorado.edu/en/simulation/radio-waves Explore what you need to do to transfer
energy from the electron in the transmitting antenna to the electron in the receiving antenna. The amount
of energy transferred depends on the electron’s
A) position
B) speed
C) velocity
D) acceleration
5) An electron in orbit is accelerating. What is wrong with Rutherford’s model?
6) Look at Alice and Bob: How can atoms exist? http://perimeterinstitute.ca/videos/alice-and-bobwonderland-how-can-atoms-exist Summarize Alice’s problem. What is needed to solve it?
Rutherford’s Second Problem:
7) Look at the spectra of gases through diffraction gratings. Describe them. p. 627
8) The light is produced when an electron gives up some of its energy as a photon. Go to PhET
http://phet.colorado.edu/en/simulation/discharge-lamps Choose one atom 30 V, single electron
production, spectrometer and run in slow motion
a) Describe what happens with each electron fired. Include a diagram.
b) Describe how to produce the different colours of photons.
9) Infrared light is much lower in energy than uv light. Infrared light will be given off when the electron
A) jumps to a lower energy level
B) jumps from a lower energy level
C) makes a smaller jump
D) makes a bigger jump
10) The light emitted from atoms form line - not continuous- spectra. This evidence conflicts with
Rutherford’s solar system model because
A) the solar system is held together by gravity, not an electrical force
B) the solar system is much bigger than an atom
C) planets can orbit at any radius and energy, those of electrons only have specific values
D) all of the above
Improving Rutherford’s Model:
11) Look at PhET http://phet.colorado.edu/en/simulation/hydrogen-atom
a) What will the first three models predict for spectrum of hydrogen?
b) How was Bohr’s model different from Rutherford’s? What did it fail to explain?
c) How is DeBroglie’s model similar to a standing wave? How is it an improvement over Bohr’s model?
d) How does Schrodinger’s model improve on Bohr’s? How does this model illustrate the four concepts
of quantum physics?
12) Exploring Bohr’s mathematical model.
a) The visible lines for H atoms are violet (410 nm), blue (434 nm), green (486 nm), red (656 nm). What
energies do these colours correspond to in J? eV?
b) Bohr said that only certain energy levels were allowed for the hydrogen atom and they were given by E
= -13.6/n2 eV, where n = 1, 2, 3 etc. What are the first six energies in eV?
c) How are these energies related to the energies of the four visible colours?
d) What other colours are predicted by this model and why don’t we see them?
.
e) Bohr’s model doesn’t work for any other element and was replaced by Schrodinger’s model over 85
years ago. This model has not been replaced why aren’t you to calculate with this model?
Textbook: 12.5 p. 649 # 1 – 4, p. 660 #21-23