Lanthanide contraction

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In the lanthanide is the phenomenon that the ionic radius at the lanthanides , from lanthanum to (57) Lutetium (71) out decreases. The term was first used by the geochemist Victor Moritz Goldschmidt in his famous series "Geochemical Distribution Laws of the Elements". The decrease in the ionic radius within the group of lanthanides distinguishes them from the other subgroup elements. There one observes only a slight decrease in the radii and even an increase towards the end of the period. An analogous behavior to the lanthanide contraction can be found with the actinides , this process is called actinide contraction .

Theoretical considerations

The cause of the lanthanide contraction lies in the properties of the 4f subshell: The shape of the f atomic orbitals is very large and diffuse, so that the electrons contained there are less localized than in the other s, p and d orbitals . This means that the nuclear charge, which increases from lanthanum to lutetium, is poorly shielded - the result is a stronger attraction of the 6s and 5p electrons: The (triple positive) ions shrink.

Relativistic influences

With heavy elements such as the lanthanides, relativistic effects must be taken into account. These contribute about 10% to the lanthanide contraction. The electrons that are closer to the nucleus, such as those of the 1s orbital, have high speeds that lead to a relativistic increase in the mass of the electrons and a contraction of these inner shells. This shields the nuclear charge and relativistically destabilizes the 4f orbitals. For this reason, the 4f electrons shield the nuclear charge even worse and the result is a further contraction of the radii of the 6s and 5p orbitals.

Effects

The lanthanide contraction causes subgroup elements within a group such. T. have very similar radii. The metals zirconium and hafnium , which are listed in the periodic table, are almost the same size and show very similar chemical behavior. This is also the reason why hafnium could only be detected in a zirconium ore by means of X-ray spectroscopy in 1923 .

Individual evidence

  1. ↑ Goldschmidt, Victor M. "Geochemical Distribution Laws of the Elements", Part V "Isomorphism and Polymorphism of Sesquioxyde. The Lanthanide Contraction and Its Consequences", Oslo, 1925
  2. ^ Charles Mortimer: Chemistry (8th edition). Thieme Verlag, Stuttgart, 2003, p. 92.
  3. ↑ Pekka Pyykko: Relativistic effects in structural chemistry . In: Chem Rev.. . 88, 1988, pp. 563-594. doi : 10.1021 / cr00085a006 .

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