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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.
Among the lanthanides, lanthanum is exceptional as it has no 4f electrons as a single gas-phase atom. Thus it is only very weakly paramagnetic , unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two, ytterbium and lutetium , where the 4f shell is completely full). [ 20 ]
[1] Relatively more stable entities with unpaired electrons do exist, e.g. the nitric oxide molecule has one. According to Hund's rule, the spins of unpaired electrons are aligned parallel and this gives these molecules paramagnetic properties. The most stable examples of unpaired electrons are found on the atoms and ions of lanthanides and ...
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 ...
The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride, chlorine has a valence of 1.
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 ...
The ionic radii of the lanthanides decrease from 103 pm (La 3+) to 86 pm (Lu 3+) in the lanthanide series, electrons are added to the 4f shell.This first f shell is inside the full 5s and 5p shells (as well as the 6s shell in the neutral atom); the 4f shell is well-localized near the atomic nucleus and has little effect on chemical bonding.
A thorium atom has 90 electrons, of which four are valence electrons. Four atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, 7s, and 7p. However, the 7p orbital is greatly destabilised and hence it is not occupied in the ground state of any thorium ion. [3]