Atomic number 28

Nickel

Ni
+ phase
− phase

Shells Orbitals 3d 4s

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28 electrons in 4 shells: 2, 8, 16, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 4
Group: 10
Block: d
Standard atomic weight: 58.693(1) Da
Electron configuration: [Ar] 3d⁸ 4s²
Phase at 25 °C: solid
Melting point: 1455 °C
Boiling point: 2730 °C
Density: 8.912 g/cm³
Electronegativity (Pauling): 1.91
Discovered: 1751, Axel Fredrik Cronstedt

Neighbours in the table

Co Cu

Nickel’s subshell label, 3d⁸, said “three-d-eight”, means eight electrons in the d subshell of the third shell. Across the whole atom, [Ar] 3d⁸ 4s², the 28 electrons stand at 2, 8, 16 and 2 per shell. The 4s pair went in first, though 4s is the outer shell. A 4s electron reaches close to the nucleus; a 3d electron is more shielded from it and so lies higher in energy.

Losing electrons runs the other way. A transition metal gives up its outer s electrons before any d electron, so Ni²⁺ is [Ar] 3d⁸. Jefferson Lab gives +2 and +3 as its common oxidation states, a bookkeeping number assuming ionic bonds; Los Alamos lists 4, 3, 2, 1, −1 and −2. OpenStax explains why the top state falls late in the series: a metal can no longer be stripped of every valence electron.

An ion with a partly filled d subshell usually forms coloured complexes, and Ni²⁺, d⁸, forms a hexaaqua ion, six water molecules round the metal ion. Many nickel compounds, ATSDR adds, dissolve fairly easily in water and are green. Los Alamos calls the metal silvery white, hard, malleable, ductile and only somewhat ferromagnetic. Cronstedt found it in 1751 in kupfernickel, now called niccolite.

Where it is found

PubChem’s record puts nickel at 84 milligrams in a kilogram of crust and 5.6 × 10⁻⁴ milligrams in a litre of seawater. Los Alamos looks upward: nickel is in most meteorites, and its presence is one test that tells a meteorite from an earthly mineral. OpenStax adds: every known iron artefact from about 4000 to 2500 BC carries an iron-nickel alloy found only off Earth.

Kupfernickel is nickel arsenide, NiAs; today, Jefferson Lab says, most nickel comes from pentlandite, NiS·2FeS. Los Alamos pairs it with pyrrhotite as the ores of Sudbury, Ontario, a deposit Jefferson Lab says is believed to come from an ancient meteor impact. The US Geological Survey’s 2024 estimate has Canada at 190,000 metric tons of 3.7 million.

The Survey puts nickel resources above 350 million tons, 54 per cent in laterites, 35 per cent in magmatic sulfide deposits. The underground Eagle Mine in Michigan produced about 8,000 tons in concentrate in 2024 for smelters in Canada and overseas. Scrap, chiefly stainless steel, covered about 54 per cent of US apparent consumption.

Why it matters

Los Alamos calls nickel chiefly valuable for its alloys; the US Geological Survey puts stainless and alloy steel and nickel alloys above 85 per cent of US consumption. In steel, Jefferson Lab says, nickel adds durability and resistance to heat and acids; it goes into armour plate, vaults and machine parts. Copper-nickel tubing is built into desalination plants, and the American nickel coin is a nickel-copper alloy.

Finely divided nickel turns vegetable oil into saturated fat. Hydrogen adsorbs first, sticking to the surface, its H–H bonds breaking into Ni–H bonds. The oil’s double bonds adsorb too, each opening its π bond, the weaker of its two bonds, into Ni–C bonds. The atoms move across the surface, pair into C–H bonds, and the product lifts off. A π bond breaks more easily than a σ bond, so the reaction trades one π for two σ bonds. Those double bonds, OpenStax says, are what make a fat unsaturated.

In a nickel-cadmium cell the cathode reduces NiO₂ to Ni(OH)₂ and the cell gives about 1.2 V. Its “jelly-roll” build delivers far more current than a same-sized alkaline cell. One isotope works at airports: nickel-63, produced from stable nickel-62, ionises substances in the ion mobility spectrometers that screen passengers for drugs and explosives.

Properties

Properties of nickel Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	28
Standard atomic weight	58.693(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1455 °C	°C	Los Alamos: 1455 °C
Boiling point	2730 °C	°C	Los Alamos: 2730 °C
Density	8.912 g/cm³	g/cm³
Electronegativity (Pauling)	1.91
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸
Phase at 25 °C	solid

Safety

Nickel is a skin sensitiser, in jewellery as much as in a workshop, and PubChem’s GHS listing gives it the signal word Danger. The warning that it may cause an allergic skin reaction stands on 99.9% of its reports, and the EPA calls nickel dermatitis the commonest effect of long-term skin contact. Dust and fume at work are NIOSH’s concern, and it calls the metal a potential occupational carcinogen. The ACGIH, the industrial hygienists’ association, rates it A5, not suspected. The PubChem Laboratory Chemical Safety Summary and the NIOSH card carry the detail.

Questions

Why is nickel magnetic?

OpenStax's physics text counts nickel among the five elements with the magnetic domains that ferromagnetism needs, beside iron, cobalt, gadolinium and dysprosium. Within a domain a quantum-mechanical coupling keeps the atomic dipoles parallel, too firmly for room-temperature heat to undo in nickel; an applied field swells the aligned domains at their neighbours' expense. Sprinkled iron oxide powder shows the domain borders on a single nickel crystal. Los Alamos, more guarded, calls the metal only somewhat ferromagnetic.

Where does the name nickel come from?

From a miners' nickname. The ore looked like a copper ore and gave no copper, and miners had named it Kupfernickel, false copper, after Nickel, a deceptive little spirit in CIAAW's account. Los Alamos renders it as Old Nick's copper, Nickel being Satan. The mineral is niccolite, nickel arsenide, NiAs, and it was in this ore that the Swedish metallurgist Axel Fredrik Cronstedt discovered the metal in 1751.

Why does nickel jewellery cause a rash?

Nickel is a skin sensitiser, and the itch it sets off is nickel dermatitis. Haz-Map, on PubChem's safety pages, puts nickel allergy at up to 17 per cent of women and up to 3 per cent of men. It traces the gap to ear piercing and cheap jewellery. Sweat matters too: sulfur-rich stainless steels react with it more readily and sensitise the skin. A dimethylglyoxime spot test, Fisher's test, can show whether a piece releases nickel.

Is nickel radioactive?

Natural nickel is not: five stable isotopes make it up, and CIAAW's abundances on PubChem's record give nickel-58 about 68 per cent. Nickel-63, produced from stable nickel-62, emits beta particles and serves as an electron source, with iron-55, in electron-capture detectors. Its half-life is 99 years by CIAAW's count and 101.2 by the IAEA's Atomic Mass Data Center. Nickel-59, a cosmogenic nuclide, one made by cosmic rays, dates how long a meteorite has lain on Earth.

Which country mines the most nickel?

Indonesia, by a distance. The US Geological Survey's 2024 estimate gives it 2.2 million metric tons of nickel content; the Philippines follow at 330,000, Russia at 210,000 and Canada at 190,000. It also holds 55 million of the world's more than 130 million tons of reserves. New Caledonia's output fell about 52 per cent amid unrest and lower prices. The London Metal Exchange's average cash price came in 21 per cent under 2023's, largely on the Indonesian surplus.