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[28] [29] Lanthanum is the least volatile of the lanthanides. [30] Like most of the lanthanides, lanthanum has a hexagonal crystal structure at room temperature (α-La). At 310 °C, lanthanum changes to a face-centered cubic structure (β-La), and at 865 °C, it changes to a body-centered cubic structure (γ-La). [29]
The lanthanide ions in these complexes can readily react with oxygen and water, leading to oxidation or hydrolysis, which damages the material’s structure and reduces its efficiency. This makes handling and storage difficult, requiring protective environments like sealed containers or inert gas atmospheres.
The colors of the γ-sesquisulfides are La 2 S 3, white/yellow; Ce 2 S 3, dark red; Pr 2 S 3, green; Nd 2 S 3, light green; Gd 2 S 3, sand; Tb 2 S 3, light yellow and Dy 2 S 3, orange. [60] The shade of γ-Ce 2 S 3 can be varied by doping with Na or Ca with hues ranging from dark red to yellow, [ 49 ] [ 60 ] and Ce 2 S 3 based pigments are used ...
Here, J is the total electronic angular momentum, L is the orbital angular momentum, and S is the spin angular momentum. Because = / for electrons, one often sees this formula written with 3/4 in place of (+). The quantities g L and g S are other g-factors of an electron.
In such a case the expectation value of neither l 1 nor l 2 is a constant of motion in general, but the expectation value of the total orbital angular momentum operator L = l 1 + l 2 is. Given the eigenstates of l 1 and l 2, the construction of eigenstates of L (which still is conserved) is the coupling of the angular momenta of electrons 1 and 2.
The localized orbital corresponding to one O-H bond is the sum of these two delocalized orbitals, and the localized orbital for the other O-H bond is their difference; as per Valence bond theory. For multiple bonds and lone pairs, different localization procedures give different orbitals.
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.
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]