Question

Does actinium violate Aufbau principle?

Answer 1

Answer:

Aufbau Principle states that once the 7s orbital is filled, the next orbital to start filling is the 4f orbital, and only then we must move on to 6d orbital. But the trend observed in actinium observed is that after the 7s orbital, the 6d orbital gets filled giving it the electronic configuration $[Rn]6d^17s^2$

. Hence Actinium violates the Aufbau’s Principle.