1E.13: Ground-state electron configuration of Ag

[Nataly Antonova 1B]

Could someone explain to me would an Ag atom have electron configuration instead of ?
I thought the s orbitals are slightly lower in energy when empty and would fill up first. Does it have anything to do with fully occupied d shells being more stable? If so, how do I know when the exception applies (like in Cu and Cr)?

[Charlotte McDonough 2B]

For multi electron atoms after z=20, the 4s state is actually higher in energy than the 3d state. That only affects notation though. You essentially answered your own question, because the fully occupied d shells are indeed more stable because of symmetry of distribution of electronic charge, and this exception is consistent with other metals such as those mentioned and configurations where d4 is more stable being d5 and "taking" an electron from the s orbital.