The filling of 4f
before 5d orbital results in a regular decrease in atomic radii called
Lanthanoid contraction which essentially compensates for the expected
4 3 2 Variation in
Atomic and
Ionic Sizes
of
Transition
Metals
�aH
�/kJ mol
–1
Rationalised 2023-24
94
Chemistry
increase in atomic size with increasing atomic number The net result
of the lanthanoid contraction is that the second and the third d series
exhibit similar radii (e