Nickel

Nickel forms primarily divalent (nickelous) compounds, although examples of compounds with formal oxidation states ranging from -1 to +4 are known. Most of the salts of nickel, such as nickel chloride (NiCl ₂), nickel sulfate (NiSO₄), and nickel nitrate (Ni(NO₃)₂), are green or blue in color, and they are most commonly hydrated. Nickel ammonium sulfate (NiSO₄·(NH₄)₂SO₄·6H₂O) is used in nickel-electroplating solutions. Nickel compounds are often identified by adding an organic reagent, dimethylgloxime, which reacts with nickel to form a red, flocculent precipitate.