Electronic Configurations Of Elements And The Periodic Table

The correct order of orbital energy for a multielectron atom is determined by the general rule of orbital filling in the scheme. This rule states that the lower the sum of , the lower the energy of the orbital. In cases where two orbitals have the same value of , the orbital with the lower value will have lower energy.
- has , so its energy is relatively high.
- has , and it is higher in energy compared to .
- has , and the -orbitals are lower in energy than both and , which makes the correct order.
Thus, the correct order of the orbital energies is .

The electronic configuration of Chromium (Cr) is . Chromium has an atomic number of 24, which means it has 24 electrons. According to the Aufbau principle and Hund’s rule, the 4s orbital is filled first before the 3d orbitals. However, Cr has an exceptional configuration where one electron from the 4s orbital is promoted to the 3d orbital, leading to a half-filled configuration, which is more stable than the expected configuration.
Thus, the correct electronic configuration is .