Nickel (Ni) : atomic weight 58.71; atomic number 28; density 8.9 g/cm3; melting point 1453°C; boiling point 2732°C;
silver-white malleable metal; exists as five valences or oxidation states of −1, +1, +2, +3, and +4 (ATSDR 2005),
with +2 being the most common.