- Nickel (Ni) is a hard, ductile, silvery-white transition metal with atomic number 28, positioned in Group 10 of the periodic table.
- It has ten valence electrons—two in the 4s subshell and eight in the 3d subshell—and most commonly exhibits oxidation states of +2 and +3, though oxidation states from −1 to +4 are known. Its atomic structure consists of twenty-eight protons, typically thirty-one neutrons, and twenty-eight electrons arranged in four shells.
- Naturally occurring nickel is composed of five stable isotopes: nickel-58 (⁵⁸Ni), the most abundant at about 68.077%; nickel-60 (⁶⁰Ni) at 26.223%; nickel-61 (⁶¹Ni) at 1.140%; nickel-62 (⁶²Ni) at 3.635%; and nickel-64 (⁶⁴Ni) at 0.925%.
- Nickel is the fifth most abundant element on Earth by mass and is found both in the crust and, more significantly, in the planet’s core, where it is alloyed with iron. In the crust, it occurs mainly in minerals such as pentlandite ((Fe,Ni)₉S₈), garnierite ((Ni,Mg)₃Si₂O₅(OH)₄), and millerite (NiS). Nickel is also present in iron meteorites, typically as iron–nickel alloys like kamacite and taenite. Major producers of nickel include Indonesia, the Philippines, Russia, New Caledonia, and Canada.
- Nickel has been used for thousands of years in alloys, though it was first recognized as a distinct element in 1751 by Swedish chemist Axel Fredrik Cronstedt. While attempting to extract copper from the mineral niccolite (NiAs), he obtained a new silvery metal instead. The name “nickel” derives from the German Kupfernickel (“devil’s copper” or “false copper”), referring to miners’ frustration with ores that resembled copper but yielded none.
- Industrial uses of nickel are dominated by its role in alloys. About 68% of nickel is used in stainless steel production, where it enhances strength, corrosion resistance, and toughness. Nickel-based superalloys are essential in high-temperature applications such as jet engines, gas turbines, and chemical plants. Other important nickel alloys include Monel (nickel–copper), Inconel (nickel–chromium), and Nichrome (nickel–chromium), each with specialized uses in marine engineering, aerospace, and heating elements.
- Nickel also plays a critical role in electrochemistry. It is used in rechargeable battery systems, including nickel–cadmium (NiCd), nickel–metal hydride (NiMH), and emerging nickel-rich lithium-ion batteries for electric vehicles. Nickel’s ability to form protective oxide layers makes it suitable for electroplating, where it provides a durable, corrosion-resistant coating. Nickel catalysts are used in hydrogenation reactions, notably in the food industry for producing margarine and shortening.
- Chemically, nickel is moderately reactive, slowly oxidizing in moist air to form a thin, passivating oxide layer that protects against further corrosion. Nickel(II) compounds, such as nickel chloride (NiCl₂) and nickel sulfate (NiSO₄), are the most stable, with characteristic green colors. Higher oxidation states occur in certain complex ions and specialized compounds.
- Biologically, nickel is an essential trace element for some microorganisms and plants, often as a component of enzymes like urease. In humans, nickel has no confirmed essential role, but exposure to small amounts is generally harmless. However, nickel is a common cause of allergic contact dermatitis, particularly from jewelry, coins, and watchbands. Chronic occupational exposure to nickel dust or certain compounds can cause respiratory issues and increase cancer risk.
- Environmentally, nickel mining and smelting can lead to soil and water contamination, particularly with soluble nickel salts that can affect plant and aquatic life. Sustainable practices and recycling—especially from batteries and stainless steel scrap—are increasingly important for meeting demand while minimizing environmental impacts.
