Explain the difference between the absorption spectrum and the emission spectrum of radiation emitted by atoms
Describe the Rutherford gold foil experiment and the discovery of the atomic nucleus
Explain the atomic structure of hydrogen
Describe the postulates of the early quantum theory for the hydrogen atom
Summarize how Bohr’s quantum model of the hydrogen atom explains the radiation spectrum of atomic hydrogen
Emission and Absorption Spectra
Rydberg Formula for Hydrogen
Practice!
Practice 4.1.1
A hydrogen atom makes a transition from the n = 3 level to the n = 2 level. It then makes a transition from the n = 2 level to the n = 1 level. Which transition results in emission of the longest-wavelength photon?
A. the first transition
B. neither, because the wavelengths are the same for both transitions
C. the second transition
Check your answer: A. the first transition
Practice 4.1.2
Which of the following observations led Bohr to formulate his model of the hydrogen atom?
A. Neutrons form a diffraction pattern when scattered from a nickel crystal.
B. Electrons are observed to have wave nature.
C. A low-density gas emits a series of sharp spectral lines.
D. The peak of blackbody radiation moves to shorter wavelengths as temperature increases.
Check your answer: C. A low-density gas emits a series of sharp spectral lines.
The Bohr Model for the Hydrogen Atom
Quantized Radii of the Hydrogen Atom
where the Bohr radius is a0 = 0.529 x 10-10 m
Quantized Energies of the Hydrogen Atom
Practice!
Practice 4.1.3
What was Bohr’s quantum condition on the orbital energies in an atom?
A. Angular momentum is quantized.
B. Electron acceleration is quantized.
C. Electron energy is quantized.
D. Orbital position is quantized.
Check your answer: A. Angular momentum is quantized
Practice 4.1.4
A hydrogen atom is in its ground state. Incident on the atom are many photons each having energy of 10.5 eV. The result is which of the following?
A. The photons pass by the atom without interaction.
B. The atom is ionized.
C. The atom is excited to a higher allowed state.
Check your answer: A. The photons pass by the atom without interaction.
Discuss!
A hydrogen atom initially in its ground state absorbs a photon, which excites the atom to the n = 3 level. Determine the wavelength and frequency of the photon.
The n = 3 state of hydrogen has E3 = -1.51 eV.
(a) Why is the energy negative?
(b) What is the physical significance of the specific number 1.51 eV?
Why is there no stationary state of hydrogen with E = -9 eV?
Draw and label an energy level diagram for hydrogen. On it, show all the transitions by which an electron in the n = 4 state could emit a photon.
Physics Education Research at UNG 