1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1 still = [Ar] 4s2 3d10 4p1...

...that is, the electron configuration for Galium (31),  This is only about atomic weights,  I was just having fun!  :-)

Now the International Union of Pure and Applied Chemists has decided to display the atomic weights of 10 elements as a range, rather than a single, average value.


Those elements affected are: hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine and thallium. Some elements, such as fluorine and gold, only exist in one form, so their weights are fixed.

New Scientist: "Immutable" periodic table taken in for alterations

Electron configuration sites:

1. Electron configuration for all elements on the periodic table
2. Dr. Michael Blaber: Professor of Biomedical Sciences at Florida State University: Electronic Structure of Atoms