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The lanthanide contraction, i.e. the reduction in size of the Ln 3+ ion from La 3+ (103 pm) to Lu 3+ (86.1 pm), is often explained by the poor shielding of the 5s and 5p electrons by the 4f electrons.
In chemistry, an unpaired electron is an electron that occupies an orbital of an atom singly, rather than as part of an electron pair. Each atomic orbital of an atom (specified by the three quantum numbers n, l and m) has a capacity to contain two electrons (electron pair) with opposite spins.
For example, the electronic configuration of phosphorus (P) is 1s 2 2s 2 2p 6 3s 2 3p 3 so that there are 5 valence electrons (3s 2 3p 3), corresponding to a maximum valence for P of 5 as in the molecule PF 5; this configuration is normally abbreviated to [Ne] 3s 2 3p 3, where [Ne] signifies the core electrons whose configuration is identical ...
In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon. [16] Some lanthanum(II) compounds are also known, but they are usually much less stable.
Scandium forms a similar cluster compound with chlorine, Sc 7 Cl 12 [9] Unlike many transition metal clusters these lanthanide clusters do not have strong metal-metal interactions and this is due to the low number of valence electrons involved, but instead are stabilised by the surrounding halogen atoms. [10] LaI is the only known monohalide.
This effect is overwhelmed when the atom is positively ionised; thus Ce 2+ on its own has instead the regular configuration [Xe]4f 2, although in some solid solutions it may be [Xe]4f 1 5d 1. [11] Most lanthanides can use only three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an ...
This is determined by the variation of the shielding effect towards the nuclear charge due to the progressive filling of the 4f orbital which acts against the electrons of the 6s and 5d orbitals. The lanthanide contraction has a direct effect on the geochemistry of the lanthanides, which show a different behaviour depending on the systems and ...
The outer valence electrons are more strongly attracted by the nucleus causing the observed increase in ionization potentials. The d-block contraction can be compared to the lanthanide contraction , which is caused by inadequate shielding of the nuclear charge by electrons occupying f orbitals.