Nickel
Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slow to react with air under standard conditions because a passivation layer of nickel oxide that prevents further corrosion forms on the surface. Even so, pure native nickel is found in Earth's crust only in tiny amounts, usually in ultramafic rocks, and in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere.
Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores.
Use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as an element in 1751 by Axel Fredrik Cronstedt, who initially mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden. The element's name comes from a mischievous sprite of German miner mythology, Nickel. Nickel minerals can be green, like copper ores, and were known as kupfernickel – Nickel's copper – because they produced no copper.
Although most nickel in the earth's crust exists as oxides, economically more important nickel ores are sulfides, especially pentlandite. Major production sites include Sulawesi, Indonesia, the Sudbury region, Canada, New Caledonia in the Pacific, Western Australia, and Norilsk, Russia.
Nickel is one of four elements that are ferromagnetic at about room temperature. Alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is used chiefly in alloys and corrosion-resistant plating.
About 68% of world production is used in stainless steel. A further 10% is used for nickel-based and copper-based alloys, 9% for plating, 7% for alloy steels, 3% in foundries, and 4% in other applications such as in rechargeable batteries, including those in electric vehicles. Nickel is widely used in coins, though nickel-plated objects sometimes provoke nickel allergy. As a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation, cathodes for rechargeable batteries, pigments and metal surface treatments. Nickel is an essential nutrient for some microorganisms and plants that have enzymes with nickel as an active site.
Properties
Atomic and physical properties
Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are ferromagnetic at or near room temperature; the others are iron, cobalt and gadolinium. Its Curie temperature is, meaning that bulk nickel is non-magnetic above this temperature. The unit cell of nickel is a face-centered cube; it has lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm. This crystal structure is stable to pressures of at least 70 GPa. Nickel is hard, malleable and ductile, and has a relatively high electrical and thermal conductivity for transition metals. The high compressive strength of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to formation and movement of dislocations. However, it has been reached in Ni nanoparticles.Electron configuration dispute
Nickel has two atomic electron configurations, 3d 4s and 3d 4s, which are very close in energy; denotes the complete argon core structure. There is some disagreement on which configuration has the lower energy. Chemistry textbooks quote nickel's electron configuration as 4s 3d, also written 3d 4s. This configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d 4s energy level, specifically the 3d 4s F, J = 4 level.However, each of these two configurations splits into several energy levels due to fine structure, and the two sets of energy levels overlap. The average energy of states with 3d 4s is actually lower than the average energy of states with 3d 4s. Therefore, the research literature on atomic calculations quotes the ground state configuration as 3d 4s.
Isotopes
The isotopes of nickel range in atomic mass from to .Natural nickel is composed of five stable isotopes,,,, and, of which is the most abundant.
Nickel-62 has the highest binding energy per nucleon of any nuclide: 8.7946 MeV/nucleon. Its binding energy is greater than both iron-56| and iron-58|, more abundant nuclides often incorrectly cited as having the highest binding energy. Though this would seem to predict nickel as the most abundant heavy element in the universe, the high rate of photodisintegration of nickel in stellar interiors causes iron to be by far the most abundant.
Nickel-60 is the daughter product of the extinct radionuclide iron-60|. Due to the long half-life of, its persistence in materials in the Solar System may generate observable variations in the isotopic composition of. Therefore, the abundance of in extraterrestrial material may give insight into the origin of the Solar System and its early history.
At least 26 nickel radioisotopes have been characterized; the most stable are with half-life 76,000 years, , and . All other radioisotopes have half-lives less than 60 hours and most these have half-lives less than 30 seconds. This element also has one meta state.
Radioactive nickel-56 is produced by the silicon burning process and later set free in large amounts in type Ia supernovae. The shape of the light curve of these supernovae at intermediate to late-times corresponds to the decay via electron capture of to cobalt-56 and ultimately to iron-56. Nickel-59 is a long-lived cosmogenic radionuclide; half-life 76,000 years. has found many applications in isotope geology. has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-78, with a half-life of 110 milliseconds, is believed an important isotope in supernova nucleosynthesis of elements heavier than iron. Ni, discovered in 1999, is the most proton-rich heavy element isotope known. With 28 protons and 20 neutrons, Ni is "doubly magic", as is Ni with 28 protons and 50 neutrons. Both are therefore unusually stable for nuclei with so large a proton–neutron imbalance.
Nickel-63 is a contaminant found in the support structure of nuclear reactors. It is produced through neutron capture by nickel-62. Small amounts have also been found near nuclear weapon test sites in the South Pacific.
Occurrence
Nickel ores are classified as oxides or sulfides. Oxides include laterite, where the principal mineral mixtures are nickeliferous limonite, O, and garnierite. Nickel sulfides commonly exist as solid solutions with iron in minerals such as pentlandite and pyrrhotite with the formula Fe9−xNixS8 and Fe7−xNixS6, respectively. Other common Ni-containing minerals are millerite and the arsenide niccolite.Identified land-based resources throughout the world averaging 1% nickel or greater comprise at least 130 million tons of nickel. About 60% is in laterites and 40% in sulfide deposits.
On geophysical evidence, most of the nickel on Earth is believed to be in Earth's outer and inner cores. Kamacite and taenite are naturally occurring alloys of iron and nickel. For kamacite, the alloy is usually in the proportion of 90:10 to 95:5, though impurities may be present. Taenite is 20% to 65% nickel. Kamacite and taenite are also found in nickel iron meteorites.
Nickel is commonly found in iron meteorites as the alloys kamacite and taenite. Nickel in meteorites was first detected in 1799 by Joseph-Louis Proust, a French chemist who then worked in Spain. Proust analyzed samples of the meteorite from Campo del Cielo, which had been obtained in 1783 by Miguel Rubín de Celis, discovering the presence in them of nickel along with iron.
Compounds
The most common oxidation state of nickel is +2, but compounds of,, and are well known, and the exotic oxidation states and have been characterized.Nickel(0)
), discovered by Ludwig Mond, is a volatile, highly toxic liquid at room temperature. On heating, the complex decomposes back to nickel and carbon monoxide:This behavior is exploited in the Mond process for purifying nickel. The related nickel complex bisnickel is a useful catalyst in organonickel chemistry because the cyclooctadiene ligands are easily displaced.
Nickel(I)
Nickel complexes are uncommon, but one example is the tetrahedral complex. Many nickel complexes have Ni–Ni bonding, such as the dark red diamagnetic prepared by reduction of with sodium amalgam. This compound is oxidized in water, liberating.It is thought that the nickel oxidation state is important to nickel-containing enzymes, such as NiFe Hydrogenase|-hydrogenase, which catalyzes the reversible reduction of protons to.
Nickel(II)
Nickel forms compounds with all common anions, including sulfide, sulfate, carbonate, hydroxide, carboxylates, and halides. Nickel sulfate is produced in large amounts by dissolving nickel metal or oxides in sulfuric acid, forming both a hexa- and heptahydrate useful for electroplating nickel. Common salts of nickel, such as chloride, nitrate, and sulfate, dissolve in water to give green solutions of the metal aquo complex.The four halides form nickel compounds, which are solids with molecules with octahedral Ni centres. Nickel chloride is most common, and its behavior is illustrative of the other halides. Nickel chloride is made by dissolving nickel or its oxide in hydrochloric acid. It is usually found as the green hexahydrate, whose formula is usually written. When dissolved in water, this salt forms the metal aquo complex. Dehydration of gives yellow anhydrous.
Some tetracoordinate nickel complexes, e.g. bisnickel chloride, exist both in tetrahedral and square planar geometries. The tetrahedral complexes are paramagnetic; the square planar complexes are diamagnetic. In having properties of magnetic equilibrium and formation of octahedral complexes, they contrast with the divalent complexes of the heavier group 10 metals, palladium and platinum, which form only square-planar geometry.
Nickelocene has an electron count of 20. Many chemical reactions of nickelocene tend to yield 18-electron products.