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As I read my book, I saw its written that the Transition metals have two outermost shells incomplete.

But , as I had read earlier, that shells are filled in stepwise manner.

So how is this possible? And why don't the outermost electrons then don't jump in the inner shells?

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  • $\begingroup$ This occurs because the shells follow Hund's rule. Notice that shells are filled in order of the letter's capacity per number, not in the order of numbers. This is why the heavier elements may have one or two shells incomplete as their valency is shared between multiple numbered shells. $\endgroup$ – Frogbert Aug 28 '20 at 15:49
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    $\begingroup$ Because "shells" are a simplification, and become a supersimplification with transition metals. $\endgroup$ – Karl Aug 28 '20 at 20:22
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    $\begingroup$ I'm afraid this is really too broad. Hundreds of questions here would have to be compiled to provide a satisfactory answer. I recommend progressing a bit further in your course, which would not explain everything but would make them less confusing. $\endgroup$ – M.A.R. Aug 30 '20 at 11:57