Apparent anomalies in the filling of electron orbitals in atoms occur in chromium and copper. In these elements an electron expected to occupy an s-orbital occupies a d-orbital instead.

(a) Explain why these anomalies occur.

(b) Similar anomalies are known to occur in seven other elements of the d-block. Using Appendix 2C, identify those elements and indicate for which ones the explanation used to rationalize the chromium and copper electron configurations is valid.

(c) Explain why there are no elements in which electrons fill (n + 1)s-orbitals instead of np-orbitals.