Science Education Home Home Teachers Students Games Videos VA SOL Programs

Questions and Answers

Why do the electron shells begin being named with K, L, M, N, and not with A, B, C?

The names of the electron shells come from a fellow named Charles G. Barkla, a spectroscopist who studied the X-rays that are emitted by atoms when they are hit with high energy electrons. He noticed that atoms appeared to emit two types of X-rays. The two types of X-rays differed in energy and Barkla originally called the higher energy X-ray type A and the lower energy X-ray type B. He later renamed these two types K and L since he realized that the highest energy X-rays produced in his experiments might not be the highest energy X-ray possible. He wanted to make certain that there was room to add more discoveries without ending up with an alphabetical list of X-rays whose energies were mixed up.

As it turns out, the K type X-ray is the highest energy X-ray an atom can emit. It is produced when an electron in the innermost shell is knocked free and then recaptured. This innermost shell is now called the K-shell, after the label used for the X-ray. Barkla won the 1917 Nobel Prize for Physics for this work.


Steve Gagnon, Science Education Specialist (Other answers by Steve Gagnon)

Related Pages:

Citation and linking information

For questions about this page, please contact Steve Gagnon.