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Gaseous chromium has a ground-state electron configuration of 3d 5 4s 1. It is the first element in the periodic table whose configuration violates the Aufbau principle. Exceptions to the principle also occur later in the periodic table for elements such as copper, niobium and molybdenum. [17]
The valence electrons (here 3s 2 3p 3) are written explicitly for all atoms. Electron configurations of elements beyond hassium (element 108) have never been measured; predictions are used below. As an approximate rule, electron configurations are given by the Aufbau principle and the Madelung rule.
Chromium and copper have electron configurations [Ar] 3d 5 4s 1 and [Ar] 3d 10 4s 1 respectively, i.e. one electron has passed from the 4s-orbital to a 3d-orbital to generate a half-filled or filled subshell. In this case, the usual explanation is that "half-filled or completely filled subshells are particularly stable arrangements of electrons".
Its members are chromium (Cr), molybdenum (Mo), tungsten (W), and seaborgium (Sg). These are all transition metals and chromium, molybdenum and tungsten are refractory metals. The electron configuration of these elements do not follow a unified trend, though the outermost shells do correlate with trends in chemical behavior:
An example is chromium whose electron configuration is [Ar]4s 1 3d 5 with a d electron count of 5 for a half-filled d subshell, although Madelung's rule predicts [Ar]4s 2 3d 4. Similarly copper is [Ar]4s 1 3d 10 with a full d subshell, and not [Ar]4s 2 3d 9. The configuration of palladium is [Kr]4d 10 with zero 5s electrons.
Thus, the aquo ion is a weak acid, of comparable strength to acetic acid (pK a of about 4.8). This pK a is typical of the trivalent ions. The influence of the electronic configuration on acidity is shown by the fact that [Ru(H 2 O) 6] 3+ (pK a = 2.7) is more acidic than [Rh(H 2 O) 6] 3+ (pK a = 4), despite the fact that Rh(III) is expected to ...
Note that these electron configurations are given for neutral atoms in the gas phase, which are not the same as the electron configurations for the same atoms in chemical environments. In many cases, multiple configurations are within a small range of energies and the small irregularities that arise in the d- and f-blocks are quite irrelevant ...
Chromium(III) chloride (also called chromic chloride) is an inorganic chemical compound with the chemical formula Cr Cl 3.It forms several hydrates with the formula CrCl 3 ·nH 2 O, among which are hydrates where n can be 5 (chromium(III) chloride pentahydrate CrCl 3 ·5H 2 O) or 6 (chromium(III) chloride hexahydrate CrCl 3 ·6H 2 O).