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A Quantum Theory for Atomic Structure

Pauli and Spinning Electrons

 
 

 

Just as the earth spins on its axis as it orbits the sun, so the electron spins on its axis as it orbits the nucleus.

 

This was not the end of the matter. Even more accurate experiments revealed additional spectral lines. This was called the 'Anomalous Zeeman Effect' and it drove the Austrian (but later Swiss) theoretician Wolfgang Pauli crazy! Pauli realized that an, as yet, observed property of the electron needed to be accounted for. He wondered if the electron could spin around its own axis as it orbited the nucleus – just as the spinning earth revolves around the sun. In the end, he found the idea unsatisfactory and never published it. A pair of Dutch physicists in their mid-twenties, George Uhlenbeck and Sam Goudsmit beat Pauli to it and published the idea of electron spin. Pauli's lack of conviction cost him the claim to the idea of electron spin.

The theory predicted that electrons can be described as either 'spin-up' or 'spin-down'. Nothing is simple in the quantum world though. The electron must perform two revolutions in order to return to the same point! Pauli was not discouraged and went on in 1925 to explain why everyday objects are solid, i.e.: why all the electrons do not fall into the nucleus, which would make all atoms unstable. This was a big problem with Bohr's solar system model of the atom. Pauli stated that no two electrons are allowed to be in the same quantum state. This means that each shell of atomic orbits could only contain a maximum of two electrons – one with spin up and the other with spin down. Pauli had quantised space and he was only 25 years old! From these ideas the periodic table (proposed by Mendeleev in 1890) could now be explained from first principles. Pauli eventually won the 1945 Nobel Prize in Physics for his achievements.

 

Related Laureates

 The Nobel Prize in Physics 1922 - Niels Henrik David Bohr »  The Nobel Prize in Physics 1945 - Wolfgang Pauli »  
 



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