Interesting quotes from Niels Bohr “Anyone who is not shocked by quantum theory has not understood it” “An expert is a man who has made all the mistakes which can be made in a very narrow field” Niels Bohr

A Brief History of Niels Bohr Born in 1885 Bohr’s father was a professor of physiology in Denmark. His brother became a renowned mathematician In 1911, Bohr received his doctorate in Physics Bohr went to work in J. J. Thomson’s lab as a theoretical physicist. He next worked in Ernest Rutherford’s lab.

A Brief History of Niels Bohr, continued It was in Rutherford’s lab Bohr developed his model of the atom improving the Rutherford model He was awarded the Nobel Prize in Physics (1922) Debated quantum mechanics with Einstein in the 20’s Left Denmark (and escaped the Germans) at the beginning of WWII and spent time at Los Alamos during atomic bomb development

What was the Rutherford Model? Remember the Gold Foil Experiment? What did Rutherford conclude about the atom?

… and Rutherford got a Nobel Prize in CHEMISTRY!!

-The Rutherford Model had a small area of positive charge -Most of the atom is empty space -Cloud of electrons orbit the area of positive charge (Rutherford originally did not use the term nucleus) One representation of the Rutherford Model

Another representation of Rutherford’s cloud of electrons ee ee e e e

Problem with the Rutherford Model This model couldn’t exist based on classical mechanics (from Newton) Electrons should lose energy and collapse into the nucleus

Niels Bohr was a theoretical physicist. That is, he used data from other scientists instead of performing experiments. Bohr saw the problem with the Rutherford model and classical mechanics. He added the concept of energy in quanta from Planck to Rutherford’s Model. This helped to explain the emission spectrum of hydrogen

Main Concepts of Bohr’s Model 1. Electrons assume only certain orbits around the nucleus. These orbits are stable and called "stationary" orbits. 2. Each orbit has an energy associated with it. For example the orbit closest to the nucleus has an energy E1, the next closest E2 and so on. 3. Light is emitted when an electron jumps from a higher orbit to a lower orbit and absorbed when it jumps from a lower to higher orbit. Only whole number jumps allowed.

Main Concepts of Bohr’s Model 4. The energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies. A picture of Bohr’s model

Bohr’s model did an excellent job explaining hydrogen emission spectrum but was inadequate to explain any other element.

On to quantum mechanics………………………..

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