 Although cadmium usually has an oxidation state of + 2 , it also exists in the + 1 state . Cadmium and its congeners are not always considered transition metals , in that they do not have partly filled d or f electron shells in the elemental or common oxidation states . Cadmium burns in air to form brown amorphous cadmium oxide ( CdO ) ; the crystalline form of this compound is a dark red which changes color when heated , similar to zinc oxide . Hydrochloric acid , sulfuric acid , and nitric acid dissolve cadmium by forming cadmium chloride ( CdCl2 ) , cadmium sulfate ( CdSO4 ) , or cadmium nitrate ( Cd ( NO3 ) 2 ) . The oxidation state + 1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride , forming the Cd22 + cation , which is similar to the Hg22 + cation in mercury ( I ) chloride . 
 Although cadmium usually <a href='got' title='1'><mark>has</mark></a> an oxidation state of + 2 , it also <a href='uninflect' title='2'><mark>exists</mark></a> in the + 1 state . Cadmium and its congeners are not always considered transition metals , in that they do not <a href='been_done' title='3'><mark>have</mark></a> partly filled <a href='negative_concord' title='4'><mark>d</mark></a> or f electron shells in the elemental or common oxidation states . Cadmium burns in air to form brown amorphous cadmium oxide ( CdO ) ; the crystalline form of this compound is a dark red which <a href='uninflect' title='5'><mark>changes</mark></a> color when heated , similar to zinc oxide . Hydrochloric acid , sulfuric acid , and nitric acid dissolve cadmium by forming cadmium chloride ( CdCl2 ) , cadmium sulfate ( CdSO4 ) , or cadmium nitrate ( Cd ( NO3 ) 2 ) . The oxidation state + 1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride , forming the Cd22 + cation , which <a href='drop_aux' title='6'><mark>is</mark></a>similar to the Hg22 + cation in mercury ( I ) chloride . 
Although cadmium usually got an oxidation state of + 2 , it also exist in the + 1 state . Cadmium and its congeners ain't always considered transition metals , in dat they do not done partly filled no d or f electron shells in the elemental or common oxidation states . Cadmium burns in air to form brown amorphous cadmium oxide ( CdO ) ; the crystalline form of this compound is a dark red which change color when heated , similar to zinc oxide . Hydrochloric acid , sulfuric acid , and nitric acid dissolve cadmium by forming cadmium chloride ( CdCl2 ) , cadmium sulfate ( CdSO4 ) , or cadmium nitrate ( Cd ( NO3 ) 2 ) . The oxidation state + 1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride , forming the Cd22 + cation , which similar to the Hg22 + cation in mercury ( I ) chloride .