Notes On d-Block: Variation In Atomic And Ionic Sizes - CBSE Class 12 Chemistry
The atomic radii of elements of the 3d-series gradually decrease in radius with an increase in atomic number. Reason: The d-orbitals offer poor shielding effect. Hence, the nuclear charge attracts all the electrons more strongly, resulting in a contraction in size. The same trend is observed in the ionic radii of a given series. The atomic radii increase from 3d to 4d, the atomic radii of the 4d and 5d transition series are very close. This is due to lanthanoid contraction. The consequence of lanthanoid contraction: The radii of the second and third transition series, that is, 4d and 5d are similar. EX: Zirconium and Hafnium. A decrease in the metallic radius along with an increase in the atomic mass results in a general increase in the density of these elements. Thus, there is a significant increase in the density from titanium to copper.

#### Summary

The atomic radii of elements of the 3d-series gradually decrease in radius with an increase in atomic number. Reason: The d-orbitals offer poor shielding effect. Hence, the nuclear charge attracts all the electrons more strongly, resulting in a contraction in size. The same trend is observed in the ionic radii of a given series. The atomic radii increase from 3d to 4d, the atomic radii of the 4d and 5d transition series are very close. This is due to lanthanoid contraction. The consequence of lanthanoid contraction: The radii of the second and third transition series, that is, 4d and 5d are similar. EX: Zirconium and Hafnium. A decrease in the metallic radius along with an increase in the atomic mass results in a general increase in the density of these elements. Thus, there is a significant increase in the density from titanium to copper.

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