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The sesquisulfides are insulators but some of the Ln 3 S 4 are metallic conductors (e.g. Ce 3 S 4) formulated (Ln 3+) 3 (S 2−) 4 (e −), while others (e.g. Eu 3 S 4 and Sm 3 S 4) are semiconductors. [18] Structurally the sesquisulfides adopt structures that vary according to the size of the Ln metal.
A mnemonic is a memory aid used to improve long-term memory and make the process of consolidation easier. Many chemistry aspects, rules, names of compounds, sequences of elements, their reactivity, etc., can be easily and efficiently memorized with the help of mnemonics.
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 other two p-orbitals, p y and p x, can overlap side-on. The resulting bonding orbital has its electron density in the shape of two lobes above and below the plane of the molecule. The orbital is not symmetric around the molecular axis and is therefore a pi orbital. The antibonding pi orbital (also asymmetrical) has four lobes pointing away ...
In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states.
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.
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.
For transition metals, the number of valence electrons ranges from 3 to 12 (ns and (n−1)d orbitals). For lanthanides and actinides, the number of valence electrons ranges from 3 to 16 (ns, (n−2)f and (n−1)d orbitals). All other non-valence electrons for an atom of that element are considered core electrons.