Q.
Among the following transition elements, which one has the highest second ionisation energy?
(i)V(Z=23)(ii)Cr(Z=24)(iii)Mn(Z=25)(iv)Ti(Z=22)
1490
211
NTA AbhyasNTA Abhyas 2020The d-and f-Block Elements
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Solution:
The general trend observed in the second ionisation enthalpy of 3d− series elements is that as we move from left to right in the period, the ionisation energy increases. But, Cr and Zn are exceptions to this trend. The value of second ionisation energy for Cr is more than Mn . This can be explained based on the electronic configuration of their M+ ions:
_24Cr+=[Ar]3d5 and _25Mn+=[Ar]3d54s1
Cr+ has a stable electronic configuration because of half-filled d− subshell. Thus removing an electron from it is difficult. Therefore, Cr has the highest second ionisation energy among the given elements.
The correct order for second ionisation energy for the given elements is Ti<V<Mn<Cr .