Nickel (Ni) [Chemical Abstracts Service (CAS) No.
7440-02-0]: 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.