Explain the variation of atomic radii in the first series of transition elements

Variation of atomic radii in transition elements

The atomic radii of elements of a particular series decrease gradually up to the midway element (from Sc to Mn) and then these values remain almost constant up to the elements of group 1B (Fe-Cu). The last element of each series i.e. Zn shows an increase in atomic radius.

 Reason

For elements from Sc to Mn, the atomic radii decrease because of gradual increase in nuclear charge with increase in atomic number. From Fe to Cu, the atomic radii remain almost constant because electrons added to the d-orbital screen the 4s electron(s), and the attraction between the nucleus and 4s electrons decreases. The additional nuclear charge is counter balanced by the screening effect.

Towards the end of the series, there is an increase in electron-electron repulsion between the electrons added to 3d and 4s orbitals. This increase in repulsion becomes greater than the attraction between the nucleus and the 4s electrons, thus, because of the greater magnitude of electron-electron repulsion, the atomic size of Zn is greater than that of Cu.

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