Question

The filling of which orbital is represented by the transition metals in period 4?

Answer 1

The 3d sublevel is being filled in the transition metals in period 4. There are five d-orbitals in any d sublevel, so there are a total of 10 electrons possible in a d sublevel (2 electrons per orbital).

Explanation:

The electron configuration of scandium (Sc), the first transition metal in period 4 is `"[Ar]3d"^(1)"4s"^2"`, and zinc (Zn), the 10th and last transition metal in period 4, is `"[Ar]3d"^(10)"4s"^2"`. Chromium, nickel, and copper, all in period 4, have unexpected electron configurations from what you would expect from the Aufbau principle. However, experimental evidence supports the unexpected configurations. They still have electrons in the 3d sublevel.