How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.

The first ionisation energies of the elements of the transition series

How would you account for the following: The d1 configuration is very unstable in ions.

How would you account for the following? The atomic radii of the metals of the third (5d) series of transition elements are virtually the same as those of the corresponding members of the second (4d) series.

How would you account for the following : SF_(6) is kinetically inert.

The second ionisation enthalpies of both chromium and copper are higher than those of the next element. Why?

How would you account for the following : XeF_2 is a linear molecule without a bend.

How would you account for the following : The transition elements exhibit high enthalpy of atomization.

How would you account for the following ? The third ionization enthalpy of manganese (Z = 25) is exceptionally high.

How would you account for the fact that Ni(CO)_4 has tetrahedral geometry?