Nickel

Nickel is a metallic chemical element with the symbol Ni and atomic number 28.

Characteristics

Nickel is a silvery white metal that takes on a high polish. It belongs to the transition metals, and is hard and ductile. It occurs most usually in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel glance.

It is clear that in common with massive forms of chromium, aluminium and titanium metal that nickel is very slow to react with air, but it is a very reactive element.

Because of its permanence in air and its inertness to oxidation, it is used in coins, for plating iron, brass, etc., for chemical apparatus, and in certain alloys, such as German silver. It is magnetic, and is very frequently accompanied by cobalt, both being found in meteoric iron. It is chiefly valuable for the alloys it forms, especially many superalloys, and particularly stainless steel.

Nickel is one of the five ferromagnetic elements. However, the U.S. “nickel” coin is not magnetic, because it actually is mostly (75%) copper. The Canadian nickel minted at various periods between 1922-81 was 99.9% nickel, and these are magnetic. Nickel is also a naturally magnetostrictive material, meaning that in the presence of a magnetic field, the material undergoes a small change in length. In the case of Nickel, this change in length is negative (contraction of the material), which is known as negative magnetostriction.

The most common oxidation state of nickel is +2, though 0, +1, +3 and +4 Ni complexes are observed. It is also thought that a +6 oxidation state may exist, however, results are inconclusive.

The unit cell of nickel is a face centred cube with a lattice parameter of 0.356 nm giving a radius of the atom of 0.126 nm.

Nickel-62 is the most stable nuclide of all the existing elements; it is more stable even than Iron-56.

Biological role

Nickel plays numerous roles in biology, though they were not recognized until the 1970s. In fact urease (an enzyme which assists in the hydrolysis of urea) contains nickel. The NiFe-hydrogenases contain nickel in addition to iron-sulfur clusters. Such [NiFe]-hydrogenases characteristically oxidise H₂. A nickel-tetrapyrrole coenzyme, F430, is present in the methyl coenzyme M reductase which powers methanogenic archaea.

One of the carbon monoxide dehydrogenase enzymes consists of an Fe-Ni-S cluster.

Other nickel-containing enzymes include a class of superoxide dismutase and a glyoxalase.