Sat January 21, 2012 By: Kanwal Sandhu

what is reorganisation energy? how does it affect the ionisation enthalpies along a series of transition elements?

Expert Reply
Fri January 27, 2012

In a one-electron transfer reaction:

The reorganization energy is defined as the energy required for all structural adjustments (in the reactants and in the surrounding solvent molecules) which are needed in order that A and D assume the configuration required for the transfer of the electron.

With increasing nuclear charge, there is an increase in magnitude of ionization enthalpy along each series of the transition elements from left to right.

But there is observed an irregular trend in the first ionization enthalpy of the 3d metals. It though of little chemical significance and can be accounted for by considering that the removal of one electron that alters the relative energies of 4s and 3d orbitals. So the mono positive ions have dn configurations with no 4s electrons. Hence there is a reorganisation energy which accompanies ionization with some gains in exchange energy as the number of electrons increases and from the transfer of s electrons into d orbitals and there is expected increasing trend in the values as the effective nuclear charge increases. So, basically reorganization energy helps in the ionization of elements and hence there is increase in ionization energy along the transition series.

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