The lanthanoid contraction is caused by imperfect shielding of one 4f electron by another, similar to the shielding observed in an ordinary transition series. However, the shielding effectiveness of 4f electrons is less than that of d electrons, leading to ...

The lanthanoid contraction occurs when 4f orbitals are filled before the 5d series begins, resulting in a regular decrease in atomic radii. This phenomenon compensates for the expected increase in atomic size with increasing atomic number and causes the third ...

The decrease in ionic radius within a series occurs because, as the atomic number increases, a new electron enters a d orbital for each unit increase in nuclear charge. The less effective shielding of d electrons leads to increased electrostatic ...

Transition metals with very high enthalpy of atomization, corresponding to very high boiling points, tend to be noble in their reactions. The enthalpy maxima at about the middle of each series indicate that having one unpaired electron per d orbital ...