Like vanadium, chromium shows a wide range of oxidation states and colours of compounds; its name derives from the Greek ‘chromos’ meaning colour. The green colour of emeralds is due to the presence of chromium in the mineral beryl, and the colour of ruby is due to the substitution of CrIII ions for AlIIIions in the structure of α-Al203. Chromium is the first element of group VIa, lying above molybdenum and tungsten. The ground state outer electronic configuration is 3d5 4s1, and like Ti and V it shows the highest oxidation state corresponding to the loss of all these outer electrons, that is +6 for Cr. Like V(v), however, Cr(vi) is a strongly oxidising state, chromium being bonded to fluorine or oxygen in its compounds. All oxidation states down to −2 are known in chromium compounds but the +3 state is by far the most stable and common.
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