Why Is the d Shell Filled Before s in Certain Transition Metals?

[TT0]

Homework Statement

The metal with the electron shell configuration of [Ar] 3d10 s1 is

A. Cu
B. Ag
C. Au
D. Zn
E. Al

Homework Equations

-[/B]

The Attempt at a Solution

I don't really know how because shouldn't the s shell be filled before the d shell in period 4?

Thanks!

 

[sushiroll]

Some electron configurations differ from those assigned using the aufbau principle because half filled sublevels are not as stable as filled sublevels but are more stable than other electron configuration. For example in copper, the 4s electron promotes itself to the 3d sublevel. Originally, the 3d sublevel would have 9 electrons, making it a partially filled d sublevel. If the 4s electron promotes itself to the 3d sublevel, the 3d sublevel would then be completely filled and the 4s sublevel half filled.

 

[TT0]

Thanks, is this for a specific area on the transition metals or is there no specific area?

 

[DrClaude]

Irregularities to the Aufbau principle for d and s electrons occur in the 5th to 11th columns of the periodic table, so it covers most transition metals. Note that there are no strict rules there either, for instance:
Ni: 3d⁸ 4s²
Pd: 4d¹⁰
Pt: 5d⁹ 6s¹