Chromium, higher valence states

Many of the transition elements exhibit more than one valence state, resulting from the possible removal of successive electrons from the inner partially filled d subshell. These d electrons may be removed singly or in groups thus the various oxidation states of an element may differ by one unit or hy more than one unit. As examples, the important oxidation states of vanadium are +3, +4, and +5 those for chromium are +2, + 3, and +6 and those for manganese are +2, +3, +4, +6, and +7. Among families of transition metals, the higher valence states become the more stable near the bottom of each family for example, in the chromium group the stability of the +6 states decreases in the order ... 

The behavior along CPE varies according to the metal. The current density along CD remains fairly constant for metals such as iron, chromium and stainless steel as the potential increases the metal continues to dissolve at 100 percent efficiency. Along DE the metals dissolve in their higher valence state but at low current efficiency, since evolution of oxygen, or other anodic reaction where possible, now occurs. The film which forms on these metals is apparently very thin and readily allows the transitions of electrons from the anion to the metal by conduction or the tunnel effect. 

Chromium has divalent, trivalent and hexavalent ions. The divalent state is unstable in water, producing hydrogen whilst being oxidised to a higher valency state (Baes and Mesmer, 1976). Chromium(lll) has a large range of stability, whereas chromium(VI), unlike vanadium(V), only forms anionic species and, as such, will... 

Ground-state electronic configuration is ls 2s 2p 3s 3p 3i 4s. Manganese compounds are known to exist in oxidation states ranging from —3 to +7 (Table 2). Both the lower and higher oxidation states are stabilized by complex formation. In its lower valence, manganese resembles its first row neighbors chromium and especially iron ia the Periodic Table. Commercially the most important valances are Mn, Mn ", or Mn ". ... 

The oxidation of tartaric and glycollic acid by chromic acid also induces the oxidation of manganous ions. In the presence of higher concentrations of manganese(II) the rate of oxidation of the acids is diminished to about one-third of that in the absence of manganous ions. The decrease of the rate has been attributed to manganese(II) catalysis of the disproportionation of the intermediate valence states of chromium probably chromium(IV). 

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