Electron shell configurations of the first 18 elements
The electron shell configurations of the first 18 elements in the periodic table. The corresponding energy levels (n) are listed in green numbers to the left. The number of outer-shell electrons is represented by the right-most digit in the group numbers.
Source
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"Periodic properties of the elements."
http://www.chem1.com/acad/webtext/atoms/atpt-6.html#ORG
Steve Lower
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