Periodic table lanthanide contraction effect

In the lanthanides an increase of 14 in atomic number occurs without change in occupation of the outermost orbital, 6s, and without a comparable increase in d shell screening effect. The atomic radii fall from La (1.69) to Lu (1.56) and the ionic radii of the ions even more, from 1.06 to 0.85 A. This lanthanide contraction affects the size of the subsequent atoms and ions in the Periodic Table. 

Apart from studies on single molecules or homologous molecules for the analysis of vertical trends in the periodic table of the elements, some interesting chemical and physical effects—such as lanthanide contraction, phosphorescence phenomena and parity violation—that are perfect areas to be tackled by four-component methods have been investigated. Some of the latest results are discussed in the following subsections. 

In the periodic system, the lanthanide group of elements also gives rise to a peculiar phenomenon, called the lanthanide contraction. This phenomenon is the important and progressive decrease in atomic radii and in radii of ions when going from lower to higher atomic numbers in the lanthanide series. Thus lanthanum has the largest atomic radius, and lutetium has the smallest. In Table 3.3, the ionic radii for the lanthanides are given, and the effect described above can be clearly seen in Fig. 3.2. 

In the rows of the periodic system, the valence electrons always shield themselves in an imperfect way from the nuclear charge. This results in an increase in effective nuclear charge, when moving from left to right in a row in the periodic system. The lanthanides show contraction of the atomic and ionic radii, due to the imperfect shielding of the valence f-orbitals. Because there are 14 elements in this series, the effect is more pronounced than other rows of the periodic table. Because the 4f-orbitals are limited in size, the size of the lanthanide ions is defined by their 5 s and 5p orbitals (Platt 2012). 

The most well-known incomplete-screening effect in the periodic table, the lanthanide contraction, is due to the successive Ailing of the 4f-shell by 14 electrons, leading to a contraction of the size of the later lanthanides and of the elements... 

The filling of inner / shells in lanthanide and actinide atoms is accompanied by a steady decrease of the size of the atom (measured by suitable means such as the first radial moment). As a consequence, the size of atoms from the same group in the second and third transition metal series of the periodic table turns out to be similar. That is, the increased number of electrons with increasing nuclear charge number Z does not lead to an increased size of the atom under consideration. This reduced-size effect is called the lanthanide contraction. It is important to understand that the effect is also witnessed in purely nonrelativistic calculations — the effect is simply amplified in a relativistic description. 

Consequences of lanthanide contraction Lanthanide contraction has a significant effect on the relative properties of elements which come before and after the lanthanides in the periodic table. Some of these effects are given below ... 

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