Search results
Results from the WOW.Com Content Network
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 rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), [1] are a set of 17 nearly indistinguishable lustrous silvery-white soft heavy metals.
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 ...
When it reacts with water, lanthanum hydroxide is formed: [37] a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric carbon dioxide to form the basic carbonate. [38] Lanthanum fluoride is insoluble in water and can be used as a qualitative test for the presence of La 3+.
Valence bond theory views bonds as weakly coupled orbitals (small overlap). Valence bond theory is typically easier to employ in ground state molecules. The core orbitals and electrons remain essentially unchanged during the formation of bonds. σ bond between two atoms: localization of electron density Two p-orbitals forming a π-bond.
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.
For instance, the lone pairs of water are usually treated as two equivalent sp x hybrid orbitals, while the corresponding "nonbonding" orbitals of carbenes are generally treated as a filled σ(out) orbital and an unfilled pure p orbital, even though the lone pairs of water could be described analogously by filled σ(out) and p orbitals (for ...
The bond valence method or mean method (or bond valence sum) (not to be mistaken for the valence bond theory in quantum chemistry) is a popular method in coordination chemistry to estimate the oxidation states of atoms. It is derived from the bond valence model, which is a simple yet robust model for validating chemical structures with ...