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I really believe that the following sentences have to be cleaned up:
"Elemental copper should have 11 electrons in the outermost shell. But, its electronic configuration is [Ar].3d10.4s1 instead of [Ar].3d9.4s2 due to the greater stability of a half-filled or fully-filled orbital. Similarly, chromium takes the electronic configuration of [Ar].3d5.4s1 instead of [Ar].3d4.4s2."
Actually, elemental copper should have 9 electrons in 3d subshell and it has 10 instead. In both examples ([Ar].3d10.4s1 and [Ar].3d9.4s2) it has (not "should have") 11 electrons in 4th shell N.
Also, what phrase "due to the greater stability of a half-filled or fully-filled orbital" mean? Shouldn't it be "due to the greater stability of a half-filled than fully-filled 4s orbital" instead?
Also, the article states that the Madelung (n+l) Rule is "Generally" followed. It is followed in all cases. This is the basis for the periodic law. (n+l) rule is followed even in regard to the elements that are regarded as exceptions. Just look at the diagram on the same page. For both, copper and chromium, as well as the elements located next to them in the Periodic Table n+l=5 for the outer most electron.
Drova (talk) 12:11, 26 May 2008 (UTC)