The group 17 elements of the periodic table have 7 valence electrons and are highly reactive, with low melting and boiling points. The halogens - including fluorine, chlorine and bromine - have a common tendency to form salts, but they are all of a toxic nature.
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For the compound formed to be neutral, the charge should be zero. This means that the positive charge should be equal to the negative charge. The balanced chemical reaction forming the neutral chromium oxide is shown below.
2Cr3+ + 3O2- ---> Cr2O3
