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The lanthanide (/ ˈ l æ n θ ə n aɪ d /) or lanthanoid (/ ˈ l æ n θ ə n ɔɪ d /) series of chemical elements [a] comprises at least the 14 metallic chemical elements with atomic numbers 57–70, from lanthanum through ytterbium. In the periodic table, they fill the 4f orbitals.
For main-group elements, the valence shell consists of the ns and np orbitals in the outermost electron shell. For transition metals the orbitals of the incomplete (n−1)d subshell are included, and for lanthanides and actinides incomplete (n−2)f and (n−1)d subshells.
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 .
The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high resistivity of 615 nΩm at room temperature; in comparison, the value for the good conductor aluminium is only 26.50 nΩm. [28] [29] Lanthanum is the least volatile of the lanthanides. [30]
Lanthanide metals react exothermically with hydrogen to form LnH 2, dihydrides. [1] With the exception of Eu and Yb, which resemble the Ba and Ca hydrides (non-conducting, transparent salt-like compounds),they form black pyrophoric, conducting compounds [6] where the metal sub-lattice is face centred cubic and the H atoms occupy tetrahedral sites. [1]
The rule is based on the fact that the valence orbitals in the electron configuration of transition metals consist of five (n−1)d orbitals, one ns orbital, and three np orbitals, where n is the principal quantum number. These orbitals can collectively accommodate 18 electrons as either bonding or non-bonding electron pairs.
The history of organolanthanide chemistry highlights the integration of lanthanides into organometallic research, beginning with the discovery of lanthanides in Scandinavia in 1794. [1] The field gained significant traction following the discovery of metallocenes like ferrocene in 1951.
For example, tetrahedral d 3, d 4, d 8 and d 9 complexes tend to show larger deviations from the spin-only formula than octahedral complexes of the same ion, because "quenching" of the orbital contribution is less effective in the tetrahedral case.