http://www.ck12.org Chapter 5. Electrons in Atoms
5.2 The Bohr and Quantum Mechanical Models of the Atom
Lesson Objectives
- Describe Planck’s work with hydrogen emission spectra, and explain how this work further informed our
understanding of the atom. - Describe the discoveries of de Broglie, Schrodinger, and Heisenberg, and explain how their work led to a
revised understanding of the atom, electrons, and light. - Describe the Bohr model and the quantum model of the atom.
Lesson Vocabulary
- emission spectra: When most substances are heated to high enough temperatures that they give off light of
various wavelengths. - Heisenberg’s uncertainty principle: States that the more precisely the position of a particle is determined,
the less precisely the momentum is known in this instant, and vice versa.
Check Your Understanding
- What are some sources for light of different wavelengths?
- What is the relationship between the color of visible light and its wavelength?
Introduction
Toward the end of the 1800s, we understood light as being composed of electromagnetic radiation waves that travel at
a constant speed (c) and can be described by their wavelength (λ) or frequency (ν). However, beginning in the 1900s,
new findings emerged about the workings of the atom and the composition of matter. It began with confirmation that
light sometimes behaved as a particle, as seen in experiments on the photoelectric effect. Light particles, or photons,
were found to have a defined and measurable amount of energy. Other findings emerged at this time, showing that
not only could waves (like light) behave as a particle, but particles (such as electrons) could sometimes behave like
waves. This concept of wave-particle duality ultimately led to a revolution in our understanding of matter, light, and
how we view the universe.
Hydrogen Emission Spectra
When most substances are heated to high enough temperatures, they give off light of various wavelengths; these
are referred to asemission spectra. Planck studied the emission spectra of different objects and saw that when