General chemistryLesson 1 of 2 in the course Electronic Structure and Periodic Properties of Elements

Bohr’s Model: Hydrogen Energies, Transitions, and Limitations

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces the early picture of the atom and the problem that classical physics could not explain. It then explores the assumptions Niels Bohr used to describe the hydrogen atom.

Following Ernest Rutherford’s work, scientists pictured atoms as tiny, dense nuclei surrounded by much lighter electrons. In the planetary model, electrons orbit the nucleus in a way that resembles planets orbiting the Sun. Hydrogen is the simplest example: it has one proton in its nucleus and one electron.

All flashcards

What is a stationary state in Bohr’s model?
An allowed electron state in which the electron does not continuously emit radiation.
Why did classical physics predict that a planetary-model atom would be unstable?
An orbiting electron accelerates as its direction changes; classical electromagnetism predicts it radiates energy and spirals into the nucleus.
What is the Bohr energy equation for hydrogen-like species?
En=−kZ2/n2E_n=-kZ^2/n^2, where nn is the principal quantum number, ZZ is nuclear charge, and k=2.179×10−18 Jk=2.179\times10^{-18}\ \text{J}.
How does photon energy relate to an electron’s energy change?
The photon energy equals the magnitude of the energy change: ∣ΔE∣=∣Ef−Ei∣=hν=hc/λ|\Delta E|=|E_f-E_i|=h\nu=hc/\lambda.
What is the ionization limit in Bohr’s energy scale?
The boundary at which an electron is unbound from the nucleus, corresponding to energy E=0E=0.

Quiz questions

  1. What defines a hydrogen-like atom or ion?Answer: It has exactly one electron.
  2. For hydrogen-like species at the same principal quantum number, how does increasing nuclear charge affect the Bohr energy?Answer: The energy becomes more negative, with magnitude proportional to Z2Z^2.
  3. Why does the Bohr model not adequately describe helium?Answer: Helium has two electrons, and the model does not account for interactions between multiple electrons.
  4. What feature of hydrogen’s spectrum did Bohr’s model help explain?Answer: Its discrete spectral lines, through transitions between allowed energy levels.
  5. For a hydrogen-like species at fixed nn, what happens to the Bohr orbital radius when nuclear charge ZZ increases?Answer: The radius decreases in inverse proportion to ZZ.

Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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