1) Light behaves as both a particle and a wave, as shown by the photoelectric effect and diffraction/interference experiments. 2) Matter also exhibits wave properties, as theorized by de Broglie and demonstrated by Davisson and Germer's experiments diffracting electrons. 3) Heisenberg's uncertainty principle states that the momentum and position of a particle cannot be known simultaneously at the atomic scale.

1. 23-3 Quantum Mechanics

2. The Dual Nature of Light A. Light is both a wave and a particle. 1. The photoelectric effect is an example of light behaving as a particle (photon). 2. Diffraction and interference are examples of light acting as a wave. A single photon’s energy is too small to detect but a “trillion” photons together behave as a wave.

3. II. Matter Waves Louis De Broglie theorized that all matter exhibits wave properties! We don’t notice because the effect is so small on objects larger than subatomic particles.  =h/p; p=mxv F=E/h

4. B. Davisson and Germer discovered that electrons could be diffracted. (fig. 23-18) Supported wave theory that particles have wave properties.

5. DeBroglie waves account for the allowed orbits of Bohr’s model . There is always an integral number of electron wavelengths around each circumferrence. Explains why only certain orbits are allowed. (fig. 23-19).

6. III. The Heisenberg Uncertainty Principle It is not possible to know the location and momentum of a particle at the same time. This is because electrons and photons are so small, just shining light on them makes them move. (fig. 23-20)

7. IV. The Electron Cloud In 1926 Erwin Schrodinger proposed a wave equation that described the way matter waves change in space and time. An electron’s position is described by the Probability of finding it in a certain location!

8. Quantum mechanics also predicts that the wave function for the hydrogen atom in the ground state is symmetrical. This is called the electron cloud.

9. In Closing: The quantum model of the atom is more difficult to visualize than the Bohr model, but it is also more complete.

10. In Closing (Continued) While most scientists believe that quantum mechanics may be the final picture of the deepest levels of nature, a few continue to search for other explanations.