Subject: Periodic table

Mad Scientists;

I'm slightly confused over two points concerning the outer or "valence" shell of elements.

First, does the outer layer mean the largest "Principal Energy Level" containing one or more 
electrons, even though that layer may contain electrons from other "Principal Energy Levels".  As 
an example, the element Bismuth, #83, has an electron configuration thusly, (Xe) 4f^14, 5d^10, 
6s^2, 6p^3.  Am I correct in assuming that Bismuth has 5 electrons in it's outer layer, 6s^2 + 
6p^3, even though 5d^10 would fill between 6s & 6p ?

Second, as you know, the "Order of Filling" of shells holds true for most of the elements, but 
not all of them.  For those elements that do not obey this precise "Order of Filling", is there a 
set of rules governing their behavior in filling their shells, or have we established this order 
empirically ?

Thank you and looking forward to you reply, I remain

Yours truly,

William C. Allyn

Re: Periodic table