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The lanthanide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the lanthanide series, from left to right. It is caused by the poor shielding effect of nuclear charge by the 4f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right.
Other effects of the d-block contraction are that the Ga 3+ ion is smaller than expected, being closer in size to Al 3+.Care must be taken in interpreting the ionization potentials for indium and thallium, since other effects, e.g. the inert-pair effect, become increasingly important for the heavier members of the group.
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 ...
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 inert-pair effect is the tendency of the two electrons in the outermost atomic s-orbital to remain unshared in compounds of post-transition metals.The term inert-pair effect is often used in relation to the increasing stability of oxidation states that are two less than the group valency for the heavier elements of groups 13, 14, 15 and 16.
About 40-50% of the actinide contraction has been attributed to relativistic effects. [2] A decrease in atomic radii can be observed across the 5f elements from atomic number 89, actinium, to 102, nobelium. This results in smaller than otherwise expected atomic radii and ionic radii for the subsequent d-block elements starting with 103, lawrencium.
La 2 O 3 forms glasses of high density, refractive index, and hardness. Together with oxides of tungsten, tantalum, and thorium, La 2 O 3 improves the resistance of the glass to attack by alkali. La 2 O 3 is an ingredient in some piezoelectric and thermoelectric materials. La 2 O 3 has been examined for the oxidative coupling of methane. [10]
Lanthanites are frequently found as secondary minerals formed by the weathering of other minerals and occur as scales or tabular crystals. Originally identified at Bastnäs, Sweden, [9] they have subsequently been found in New Zealand, [10] Japan, [11] Madagascar, [12] Wales, [13] China, [14] France, [15] Germany, [16] Greenland, [17] Finland, [18] Canada, [19] Austria, [20] Romania, [21 ...