Zinc

Zinc sits at atomic number 30 with the electron configuration [Ar] 3d10 4s2, which places a completely filled d subshell between its core and its two valence electrons. That full d shell is chemically inert, meaning zinc shows almost none of the variable oxidation states that characterize its transition-metal neighbors — it exists virtually exclusively as Zn2+ in all its chemistry. This simplicity makes zinc predictable and safe: it is not redox-active under biological conditions, it does not generate damaging free radicals, and its Lewis acid character is well-controlled. With a density of 7.134 g/cm³ and an electronegativity of 1.65, zinc is a moderately soft, somewhat brittle metal with a bluish-white luster that tarnishes in air to a dull gray oxide. Its relatively low melting point of 419.5 degrees Celsius makes it easy to cast and alloy, while its ionization energy of 9.394 eV reflects the stability of its full d subshell.

Galvanization — the coating of steel with a thin layer of zinc — consumes roughly half of global zinc production and is the cornerstone of corrosion protection in construction, automotive bodies, electrical towers, and chain-link fencing. Zinc protects steel not merely as a physical barrier but electrochemically: because zinc is more reactive than iron, it acts as a sacrificial anode, corroding preferentially even when the coating is scratched. Brass — an alloy of copper and zinc containing 5 to 45 percent zinc — is the second major zinc application, valued for its machinability, acoustic properties, and corrosion resistance in musical instruments, valves, fittings, and hardware. Die casting uses zinc alloys (most commonly Zamak, a zinc-aluminum-magnesium-copper alloy) to produce precision components for automotive, hardware, and electronics industries at high throughput. Zinc oxide (ZnO) is a versatile compound used as a UV absorber in sunscreen and paints, a vulcanization activator in rubber manufacturing, and an ingredient in calamine lotion and antiseptic creams. Zinc is an essential micronutrient and dietary supplement; it is a cofactor in over 300 enzymes and plays a structural role in thousands of zinc-finger proteins that regulate gene expression.

Zinc compounds have been used since antiquity — brass was produced in the ancient Near East and Rome by co-smelting copper with zinc-containing calamine ore, even without knowledge that zinc was a distinct element. Metallic zinc was produced in India as early as the 9th century CE using distillation retorts at Zawar, Rajasthan, predating European zinc metallurgy by several centuries; Indian zinc was exported to China and the West. Andreas Sigismund Marggraf, a German chemist, is credited with isolating and characterizing zinc as a distinct element in Europe in 1746, though his process closely paralleled Indian practice. The name zinc likely derives from the German word Zink, itself of uncertain origin; one popular but unverified etymology links it to the pointed shape (Zinke, meaning 'prong' or 'tine') of zinc crystals as they solidify. In the 19th century, zinc's role in galvanic cells was established by Alessandro Volta, whose early batteries used zinc as the anode, and Luigi Galvani's famous frog-leg experiments used zinc-brass contacts.

Zinc makes up roughly 70 parts per million of Earth's crust by mass, making it the twenty-fourth most abundant element overall. It does not occur native; instead it is found primarily as zinc sulfide in the mineral sphalerite (ZnS), the dominant zinc ore, which is often associated with galena (lead sulfide) in hydrothermal vein deposits and Mississippi Valley-type deposits in carbonate rocks. Secondary zinc minerals include smithsonite (ZnCO3), hemimorphite (Zn4Si2O7(OH)2·H2O), and zincite (ZnO). The largest producers of zinc ore are China, Peru, Australia, India, and the United States. Zinc is also recycled extensively: secondary zinc from scrap accounts for roughly one-third of global supply. Trace zinc is essential to all known life; it is particularly concentrated in the hippocampus, liver, muscle tissue, and the prostate gland in humans.

Zinc oxide (ZnO) is the most commercially important zinc compound — a white powder used in rubber vulcanization, ceramic glazes, paints, sunscreens, and as a semiconductor in varistors and piezoelectric transducers. Zinc sulfide (ZnS) is the principal ore mineral sphalerite and, when doped with trace copper or silver, is the phosphor used in cathode-ray tube screens, X-ray detection screens, and glow-in-the-dark materials. Zinc chloride (ZnCl2) is a strong Lewis acid used as a flux in soldering, a wood preservative, and a reagent in organic synthesis. Zinc sulfate (ZnSO4) is used as a dietary supplement, in electrogalvanizing baths, and as a fungicide. Zinc acetate (Zn(CH3COO)2) treats zinc deficiency and is used as a mordant in dyeing. Organozinc compounds — particularly diethylzinc, the first organometallic compound containing a carbon-metal sigma bond to be recognized, synthesized by Edward Frankland in 1848 — are important reagents in asymmetric synthesis. Zinc finger proteins, where Zn2+ tetrahedrally coordinates two cysteine and two histidine residues, constitute one of the most abundant structural motifs in eukaryotic proteomes.

• Zinc is the fourth most used metal worldwide by tonnage, after iron, aluminum, and copper — a ranking driven almost entirely by its role in galvanizing steel, which extends the useful life of steel infrastructure by decades.
• Diethylzinc, the organozinc compound synthesized by Edward Frankland in 1848, is so pyrophoric that it ignites spontaneously in air; it was once proposed as a rocket fuel igniter and is still used in specialty chemistry under inert-atmosphere conditions.
• Zinc deficiency affects an estimated two billion people globally, particularly in regions where diets are dominated by phytate-rich cereal grains that inhibit zinc absorption; symptoms include impaired immune function, stunted growth, and delayed wound healing.
• The pennies minted by the United States after 1982 are 97.5 percent zinc with only a thin copper plating — a change made when rising copper prices made the all-copper penny worth more as metal than as currency.
• Zinc is the only metal whose ore, calamine, was used to make an alloy — brass — in antiquity without anyone realizing they were adding a second metal to copper; the zinc in calamine was simply absorbed by the copper during smelting without ever appearing as a distinct metallic substance.