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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 .
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]
All of the lanthanides form sesquioxides, Ln 2 O 3. The lighter/larger lanthanides adopt a hexagonal 7-coordinate structure while the heavier/smaller ones adopt a cubic 6-coordinate "C-M 2 O 3" structure. [50] All of the sesquioxides are basic, and absorb water and carbon dioxide from air to form carbonates, hydroxides and hydroxycarbonates. [57]
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.
The most famous example is Vaska's complex (IrCl(CO)(PPh 3) 2), [PtCl 4] 2−, and Zeise's salt [PtCl 3 (η 2-C 2 H 4)] −. In such complexes, the d z 2 orbital is doubly occupied and nonbonding. Many catalytic cycles operate via complexes that alternate between 18-electron and square-planar 16-electron configurations.
Since the parent ion can only be 2 P 1/2 or 2 P 3/2, the notation can be shortened to [] or ′ [], where nℓ means the parent ion is in 2 P 3/2 while nℓ′ is for the parent ion in 2 P 1/2 state. Paschen notation is a somewhat odd notation; it is an old notation made to attempt to fit an emission spectrum of neon to a hydrogen-like theory.
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.
An analogous consideration applies to water (one O lone pair is in a pure p orbital, another is in an sp x hybrid orbital). The question of whether it is conceptually useful to derive equivalent orbitals from symmetry-adapted ones, from the standpoint of bonding theory and pedagogy, is still a controversial one, with recent (2014 and 2015 ...