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. In periodic table for example Ag has an electron configuration of [Kr] 4d10,5s1 but when you do it yourself using Aufbau principle it should be [Kr] 5s2 4d9. Why is that?

When ask for Ag + valence electron configuration answers may now vary because of the existence of two electron configurations from the periodic table and using aufbau principle...


marked as duplicate by bon, ron, Todd Minehardt, Jon Custer, hBy2Py May 6 '16 at 15:57

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  • $\begingroup$ Because the Aufbau principle is not taken as gospel by the electrons busy trying to solve Schrodinger's equation. It is not a law of nature, it is more of a general guideline for chemistry students that has problems, certainly with d electrons. $\endgroup$ – Jon Custer May 6 '16 at 13:02
  • $\begingroup$ How come Sir that it serves as a general guideline if it doesn't match in what we see in the periodic table? Thank you. $\endgroup$ – Ginee M. May 6 '16 at 13:06
  • $\begingroup$ I would not expect a general guideline to precisely match every single element in the periodic table. You have already noted that it doesn't, and basically I am saying that you should not expect it to. It is not a physical law. Adding d electrons makes for some funny things, and you have noted one of them. There are others. $\endgroup$ – Jon Custer May 6 '16 at 13:49

As a general rule, full electron shells are more stable than unfilled shells. In silver, promoting an electron from the 5s to the 4d shell completes the d orbital, which increases the stability of the 4d shell more than it destabilizes the 5s shell. This is also explained here:



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