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

The properties of the elements of the first transition series differ from those of the heavier transition elements in many ways.

$(i)$ The atomic sizes of the elements of the first transition series are smaller than those of the heavier elements (elements of $2^{\text {nd }}$ and $3^{\text {rd }}$ transition series).

However, the atomic sizes of the elements in the third transition series are virtually the same as those of the corresponding members in the second transition series. This is due to lanthanoid contraction.

$(ii)$ $+2$ and $+3$ oxidation states are more common for elements in the first transition series, while higher oxidation states are more common for the heavier elements.

$(iii)$ The enthalpies of atomisation of the elements in the first transition series are lower than those of the corresponding elements in the second and third transition series.

$(iv)$ The melting and boiling points of the first transition series are lower than those of the heavier transition elements. This is because of the occurrence of stronger metallic bonding ( $M-M$ bonding ).

$(v)$ The elements of the first transition series form low-spin or high-spin complexes depending upon the strength of the ligand field. However, the heavier transition elements form only low-spin complexes, irrespective of the strength of the ligand field.