Chapter 10: Modern Atomic Theory (10.1 to 10.6)
1. a. Describe Rutherford’s model of the nuclear atom.
The model has positively charged particles called protons and neutral particles neutrons in a
small nucleus. Negatively charged particles called electrons move in some way around the nucleus and
account for the rest of the volume of the atom.
b. How did this model significantly differ from previous models?
Electrons are outside a very small nucleus. Atoms are mostly empty space.
c. What major question was left unanswered by Rutherford? Explain.
What are the electrons doing? How are they arranged and how do they move? Rutherford
could not explain what was keeping the electrons from being attracted into the nucleus.
2. What is electromagnetic radiation (ER)?
Energy being transmitted from on place to another by light.
3. ER (light) has wavelike properties, much like ocean waves. Describe the three properties of ER?
Wavelength: the distance between wave peaks (or crests).
Frequency:
the number of wave peaks that that pass by a certain point in a given time period.
Speed: how fast the wave is moving
4. Examine figure 10.4. What are the shortest wavelengths of ER? The longest?
The shortest ER wavelengths are those of gamma rays; the longest are those of radio waves.
5. What two kinds of characteristics can ER waves have?
Light can exist as waves or as particles.
6. What is a photon?
A particle of light. A beam of light can be thought of as a stream of photons, each of which s a tiny
packet of energy.
7. What is the relationship between wavelength and the energy of the photons?
Longer wavelengths correspond to photons with less energy; shorter wavelengths correspond to
photons with greater energy.
8. What happens to an atom when it receives energy from some source?
It absorbs the energy and becomes excited.
9. What do we mean by “excited state”?
This is a higher energy state. The atom has excess energy.
10. What do we mean by “ground state”?
The lowest possible energy state for the atom.
11. How can an atom go from excited to ground state?
It emits a photon of light that corresponds to the change in energy that the atom experienced in
going from an excited to a ground state.
12. Do all wavelengths have the same amount of energy?
No. Different wavelengths carry different amounts of energy per photon. Longer wavelengths
contain less energy per photon than shorter wavelengths.
13. What is the comparison between the energy of a photon of emitted light from an excited atom and the
energy the atom loses in going from the excited state to the ground state?
The energy of the photon corresponds exactly to the energy changes experienced by the emitting
atom.
14. Examine figure 10.11. What does this tell you about the photons of energy released by excited hydrogen
atoms?
The energy of the photon corresponds to the difference in energy between the excited state and the
lower energy state.
15. What does quantized mean? Describe the difference between continuous energy levels and discrete
(quantized) energy levels.
It means only certain values are allowed. In continuous energy levels any energy value is allowed.
In discrete energy levels only certain energy states are allowed. Continuous energy levels are
analogous to a ramp that varies continuously in elevation, whereas quantized energy levels are like a
flight of stairs that allow only certain elevations.
16. Describe Bohr’s model of the atom. Be sure to explain how it differs from Rutherford’s model.
Bohr’s model (of the hydrogen atom) has quantized energy levels that correspond with observed
hydrogen emission data (fig 10.11). Bohr pictured electrons travelling in allowed circular orbits that
correspond to the various allowed energy levels. Electrons could jump to different energy levels by
absorbing or emitting a photon of light with exactly the correct energy content. In Rutherford’s
model electrons were not confined to specific orbits.
17. What was the problem with the Bohr model of the atom?
It did not work for atoms other than hydrogen.
18. How does the wave-mechanical model of the atom improve on the Bohr model?
Electron states are described as orbitals, rather than orbits. The W-M model can be applied to all
atoms.
19. What are orbitals according to the wave-mechanical model?
Orbitals – also known as probability maps -- are regions of space occupied by the electrons of an
atom.
20. Read the firefly analogy (page 288, fig 10.18). How does it help explain the concept of orbitals?
Just as the precise location of the firefly cannot be predicted in advance, neither can the path of an
electron be determined in advance. Orbitals are only where electrons can probably be found at a
certain point and time. The details of electron motion can never be known.