What is the general electronic configuration of outer orbitals for transition elements, and why does Pd have a unique electronic configuration?

The general electronic configuration of outer orbitals for transition elements is (n-1)d¹⁻¹⁰ ns¹⁻². However, Palladium (Pd) has a unique electronic configuration of 4d¹⁰ 5s⁰. This deviation is due to the relatively small energy difference between the 4d and 5s orbitals. In Pd, the energy required to promote an electron from 4d to 5s is less than the energy required to add another electron to the 5s orbital. As a result, Pd achieves a more stable configuration with a completely filled 4d orbital, leading to its unique electronic arrangement compared to other transition elements.