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Here [Ne] refers to the core electrons which are the same as for the element neon (Ne), the last noble gas before phosphorus in the periodic table. 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.
Configurations of elements 109 and above are not available. Predictions from reliable sources have been used for these elements. Grayed out electron numbers indicate subshells filled to their maximum. Bracketed noble gas symbols on the left represent inner configurations that are the same in each period. Written out, these are: He, 2, helium : 1s 2
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 · n H 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 ).
Element Group Electron configuration electron configuration (P8000) Term symbol note 1, 2, S, P, 1 H hydrogen: 1 1s 1: 1s¹ : 2 S 1/2: S: 2 He helium: 18 1s 2: 1s² : 1 S 0: S: 3 Li lithium
The configuration that corresponds to the lowest electronic energy is called the ground state. Any other configuration is an excited state. As an example, the ground state configuration of the sodium atom is 1s 2 2s 2 2p 6 3s 1, as deduced from the Aufbau principle (see below).
Chromium(II) chloride describes inorganic compounds with the formula Cr Cl 2 (H 2 O) n. The anhydrous solid is white when pure, however commercial samples are often grey or green; it is hygroscopic and readily dissolves in water to give bright blue air-sensitive solutions of the tetrahydrate Cr(H 2 O) 4 Cl 2 .
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]
Chromium is a very common naturally occurring element. It is the 21st most abundant element in the Earth's crust with an average concentration of 100 ppm. The most common oxidation states for chromium are zero, trivalent, and hexavalent states. Most naturally occurring chromium is in the hexavalent state. [20]