Comment on the statement that elements of the first transition series posses many properties different from those of behavier transition elements.

Explanation

The given statement is true and it is supported by the following observations.
1. Atomic radii of the elements of 3d - series are smaller than those of the corresponding heavier transition elements (4d and 5d - series). However, atomic sizes of the elements of 4d and 5d - series are very close to each other.
2. Ionisation enthalpies of the elements of 5d - series are very much greater than the corresponding elements of 3d and 4d - series.
3. Melting point, boiling point and enthalpies of atomisation of heavier transition elements (4d and 5d - series) are greater than the corresponding elements of 3d - series. This is due to stronger intermetallic bonding in the elements of 4d and 5d - series.
4. For elements of 3d - series, + 2 and + 3 oxidation states are more common, but for the heavier elements (4d and 5d - series) higher oxidation states are more common. Thus Ru, Os and Re forms `RuO_(4), OsO_(4)` and `ReF_(7)`, respectively.
5. The elements of first transition series form low spin or high - spin complexes depending upon the strength of the ligand field. But the heavier elements (4d and 5d - series) form low - spin complexes irrespective of the strength of the ligand field.