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प्रश्न
Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following point:
Ionisation enthalpies
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उत्तर
- In every series, the first ionisation enthalpy generally increases gradually as we move from left to right, although some exceptions are observed in every series.
- In the same respective vertical column (group), the first ionisation enthalpy of some elements of the 4d series is higher, and that of some elements is lower as compared to the elements of the 3d series, although the first ionisation enthalpy of the 5d series is significantly higher as compared to the 3d and 4d series.
- The reason for this is the poor shielding effect of the 4f electrons in the 5d series (known as lanthanoid contraction), which increases the effective nuclear charge and binds the outermost electrons very tightly.
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