Lanthanoidikontraktio

Lanthanoidikontraktio is a term used in chemistry to describe the gradual decrease in atomic and ionic radii across the lanthanide series of elements. This phenomenon occurs because the 4f electrons, which are being added across the series, are poorly shielding the outer electrons from the increasing nuclear charge. As the atomic number increases, the number of protons in the nucleus also increases, leading to a stronger attraction between the nucleus and the electron shells. Despite the addition of electrons, the effect of the increased nuclear charge is dominant, causing the electron cloud to contract.

The lanthanoids are elements 57 through 71, starting with lanthanum and ending with lutetium. Within this series, there is a consistent, albeit small, reduction in size with each successive element. This contraction is not uniform and can be influenced by factors such as the oxidation state of the ion and the coordination number. For example, the ionic radii of M3+ ions decrease steadily from La3+ to Lu3+.

The consequences of lanthanoidikontraktio are significant in chemistry. It explains why elements that follow the lanthanides in the periodic table, such as hafnium, tantalum, and tungsten, have similar chemical properties and ionic radii to the elements directly above them in the same group (e.g., zirconium and niobium). This similarity can make the separation of these elements challenging. Furthermore, lanthanoidikontraktio influences the physical properties of compounds containing these elements, affecting factors like crystal structures and solubility.