IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry - Why shells or orbits are designated by K , L , M , N AND NOT BY A, B , C , D

divya.handa132

Why shells or orbits are designated by K , L , M , N AND NOT BY A, B , C , D

divya.handa132

Why shells or orbits are designated by K , L , M , N AND NOT BY A, B , C , D .

akshay.khare91

the Q is like that why ur name is divya why not other??????

spideyunlimited

The electron shell designations were started at K rather than A. The letters A-J never had to be used.

In the early twentieth century, scientists were intensely interested in X-rays, which had just been discovered. Especially fascinating was the fact that elements emit X-rays when bombarded with streams of fast-moving electrons (as in J. J. Thomson's cathode ray tube). This discovery is the basis for medical and dental X-ray machines.

When high-energy electrons hit a sample of an element, they ionize its atoms in a rather unusual way. An inner shell electron is lost in the initial impact, and when it is recaptured, a great deal of energy is released in the form of X-rays.

The X-rays emitted seemed to be of two types. One type was able to penetrate sheets of metal of a certain thickness; the other wasn't. The spectroscopist who discovered this (Charles G. Barkla) named the more penetrating type A and the less penetrating type B, initially. But he worried that even more penetrating types of X-ray radiation would be discovered for other elements, so he renamed them K and L to leave room for more penetrating types A through J. These more penetrating radiations were never observed.
Hence the shells remained names as K, L and further on.

Barkla's work was continued by Moseley and others, and eventually it became the basis for an experimental procedure for determining the atomic numbers of the elements. For his contribution, Barkla received the 1917 Nobel prize in Physics.

Today we know that Barkla's K radiation is produced when electrons knocked out of the n=1 shell are recaptured. L radiation is produced when electrons knocked out of the n=2 shell are recaptured; since the n=2 shell has higher energy than the n=1 shell, less energy is released and L radiation is weaker (less able to penetrate metals) than K radiation.

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