Explain why the actual electron configurations for chromium and copper differ from those assigned using the aufbau diagram?

Answer 1

The aufbau procedure (filling order of atomic orbitals) is used to work out the electron confiturations of all atoms. However, modification should be made by applying Hund's rule. The aufbau procedure is based on a rough energy levels diagram of many-electron atoms.

Answer 2

In electron configuration, there are many types of different energies that you need to know. With regards to this question, the two important ones are 'promotion energy' and 'spin pairing energy.'

Promotion energy is the energy needed to promote, for example, an electron from the s orbital to the p orbital, therefore the more energy needed, the harder it is to 'promote' the electron. Spin pairing energy is the energy involved with the spinning and pairing of two electrons, for example, in the s orbital.

Copper and Chromium are exceptions to the Aufbau Rule because they both have a higher spin energy than promotion energy. Because the promotion energy is lower than the spin pairing energy, it is much easier for the electron to become 'promoted' to the p orbital rather than spin and pair in the s orbital. There are a few other exceptions and some debated exceptions as well.

Answer 3

Those orbitals are more stable which are either half filled or full filled so Cr has d5 instead of d4 and Cu has d10 instead of d9.