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.
Electronic configurations play a significant role in deciding the stability of oxidation states in the first transition series, though the relationship is complex and not easily generalised. The successive ionisation enthalpies in transition elements do not increase as steeply as in main group elements. Hence, the loss of a variable number of electrons from (n-1)d orbitals is not energetically unfavourable, allowing these elements to exhibit multiple oxidation states.
The elements which give the greatest number of oxidation states occur in or near the middle of the series. For example, manganese exhibits all oxidation states from +2 to +7 due to its favourable electronic configuration.
At the beginning of the series, elements have too few electrons to lose or share. Scandium(II) is virtually unknown and titanium(IV) is more stable than Ti(III) or Ti(II), as losing all valence electrons gives a noble gas configuration.
At the other end of the series, elements have too many d electrons, resulting in fewer orbitals available for sharing electrons. Zinc shows only the +2 oxidation state as no d electrons are involved. Copper is an exception among the first series metals, being relatively less reactive.
The stability differences are illustrated by the fact that among d⁴ species, Cr²⁺ is strongly reducing while manganese(III) is strongly oxidising, showing how electronic configuration influences relative stability.
Explanation
The textbook explains that while ionisation enthalpies provide some guidance about oxidation state stability, the relationship is complex. The key concept is that successive ionisation enthalpies don't increase steeply in transition elements, making variable electron loss from (n-1)d orbitals energetically feasible. The context provides clear examples: Mn shows maximum oxidation states (+2 to +7) in the middle; Sc(II) is unknown and Ti(IV) is more stable at the beginning; Zn shows only +2 state at the end. The d⁴ configuration example (Cr²⁺ reducing vs Mn³⁺ oxidising) further illustrates how electronic configuration affects stability.