Atomic number 30

Zinc

Zn
+ phase
− phase

Shells Orbitals 3d 4s

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30 electrons in 4 shells: 2, 8, 18, 2.

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

Category: Transition metal
Period: 4
Group: 12
Block: d
Standard atomic weight: 65.38(2) Da
Electron configuration: [Ar] 3d¹⁰ 4s²
Phase at 25 °C: solid
Melting point: 419.5 °C
Boiling point: 907 °C
Density: 7.134 g/cm³
Electronegativity (Pauling): 1.65
Discovered: 1746, Andreas Sigismund Marggraf, in Europe; the metal was made in India centuries earlier

Neighbours in the table

Cu Ga

Thirty electrons make up a zinc atom, spread over four shells as 2, 8, 18 and 2 and written [Ar] 3d¹⁰ 4s². The 3d orbitals filled one group earlier, with copper’s family, so zinc’s last electron went into the 4s orbital instead. With the d shell already full, IUPAC’s definition of a transition element, which asks for partly filled d orbitals, technically leaves group 12 out. In everyday use, as in OpenStax, the name covers the whole d block.

The chemistry comes from the 4s pair. Those two electrons are easier to remove than the 3d electrons beneath them, so they leave first, and only they leave. What remains is Zn²⁺, [Ar] 3d¹⁰, an ion with eighteen electrons in its outer shell, which OpenStax calls a pseudo-noble gas configuration. Zinc is the most reactive metal in group 12, ahead of cadmium and mercury.

Los Alamos describes the metal as bluish-white and lustrous, a fair conductor of electricity, brittle at room temperature yet malleable between 100 and 150 °C. It melts at 419.5 °C, far below the transition metals proper, which OpenStax says melt above 1000 °C. The book puts such gaps down to differences in the strength of metallic bonding, the attraction between a metal’s nuclei and its sea of delocalised electrons.

Where it is found

PubChem’s element record puts zinc at 70 milligrams per kilogram of crust and 0.0049 milligrams per litre of seawater. Its ores are usually sulfides, carbonates or oxides: Los Alamos lists sphalerite, smithsonite, calamine and franklinite, the last a mixed oxide of zinc, manganese and iron.

The US Geological Survey estimates 2024 mine output at 12 million metric tons of contained zinc, China first, then Peru, Australia, India and the United States. The American 750,000 tons came from six operations in five states. Australia holds the largest reserves in the survey’s table, 64 million tons of a world total near 230 million.

Extraction begins with roasting: heating the ore in air turns it into zinc oxide. Coal then reduces the oxide to zinc vapour, since carbon is a strong enough reducing agent for most d-block metals and much cheaper than electrolysis. The crude metal carries arsenic and cadmium, which boil lower than zinc’s 907 °C, and lead and iron, which boil higher, so careful redistillation parts zinc from all four. PubChem’s record adds that most zinc today comes instead from electrolysis of aqueous zinc sulfate.

Why it matters

Galvanised steel leads American use of refined zinc, ahead of brass and die-casting alloys. OpenStax reckons about half of all zinc production goes to shielding iron and other metals from corrosion. A galvanised nail is iron under a coat of zinc, usually electroplated on. While the coat is whole it keeps air off the iron. Once scratched through, zinc can still protect. As the more active metal, the one more easily oxidised, it corrodes as a sacrificial anode while the iron, now the cathode, merely passes electrons along.

A zinc-carbon dry cell is a zinc can that is both container and anode, with a graphite rod for cathode. The paste inside holds manganese(IV) oxide, zinc chloride, ammonium chloride and water. The cell runs on the oxidation of zinc, each atom giving up two electrons to become Zn²⁺, and delivers about 1.5 V. Alkaline cells were developed in the 1950s around the same pair of reactions. They form zinc oxide at the anode and pack three to five times as much energy into a similar size.

Brass, zinc with 55 to 95 per cent copper, dates back about 2,500 years, and the Romans made coins and kettles from it. Today it goes into musical instruments, screws and hardware that must resist corrosion. The American penny is now zinc coated with copper.

Properties

Properties of zinc 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	30
Standard atomic weight	65.38(2) Da	Da	IUPAC/CIAAW 2024
Melting point	419.5 °C	°C	Los Alamos: 419.5 °C
Boiling point	907 °C	°C	Los Alamos: 907 °C
Density	7.134 g/cm³	g/cm³
Electronegativity (Pauling)	1.65
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰
Phase at 25 °C	solid

Safety

Zinc metal in everyday forms, a galvanised sheet, a brass screw or a battery can, is safe to handle: Los Alamos does not consider it toxic. PubChem’s Danger label is for zinc powder and dust, which can catch fire in air and give off hydrogen with water, and for harm to aquatic life. Burning, melting or strongly heating zinc gives off fine oxide fume, and breathing it brings on metal fume fever, an influenza-like illness delayed by up to 48 hours. It concerns people who work the metal hot; the PubChem Laboratory Chemical Safety Summary below covers the precautions.

Questions

Who discovered zinc?

No single person. Brass, an alloy of copper and zinc, was in use about 2,500 years ago, and CIAAW records zinc being recognised as a metal as early as 1374. The metal itself was first made in India by heating calamine with wool; Jefferson Lab, quoted in PubChem's record, dates that to the 1400s. Andreas Sigismund Marggraf rediscovered it in Europe in 1746 by heating calamine with charcoal.

Is zinc a transition metal?

It depends on the definition. IUPAC reserves the term for elements with partly filled d orbitals, and zinc's 3d set is full, so by that rule zinc, cadmium and mercury are technically not transition elements. Common usage, OpenStax's included, applies the name to the whole d block. The same book also counts group 12 as post-transition metals, because the last electron added is a 4s electron, and says they behave more like the alkaline earth metals.

Why does zinc fizz in hydrochloric acid?

The bubbles are hydrogen. Zinc is more easily oxidised than hydrogen, which puts it, alongside the alkali and alkaline earth metals, among the metals that displace hydrogen from acids. Each zinc atom passes two electrons to hydrogen ions from the acid, which leave as H₂ gas, while the zinc dissolves as colourless Zn²⁺ ions beside the chloride. Mercury, lower in the same group, is harder to oxidise than hydrogen and does not displace it from hydrochloric acid.

Why does zinc turn dull and grey?

Fresh zinc is silvery, and OpenStax says it quickly tarnishes to blue-grey. The colour belongs to an adherent film of basic zinc carbonate, Zn₂(OH)₂CO₃, and that film passivates the metal: it seals the surface and inhibits further corrosion. Jefferson Lab describes the same protective layer as zinc oxide. That coat is part of why zinc, aluminium and magnesium can be used in open air despite reacting with it.

Why do we need zinc in our diet?

In small amounts, as the Zn²⁺ ion. OpenStax's nutrition table names meat, fish, poultry, cheese and shellfish as its sources and links zinc to immunity, reproduction, growth, blood clotting and the working of insulin and the thyroid. It also serves as a co-enzyme in the synthesis of the heme part of haemoglobin. Going short shows as loss of appetite, poor growth, hair loss, skin problems and a dulled sense of taste or smell.

Compounds containing zinc

ZnO Zinc oxide 2 atoms in one formula unit of an ionic lattice.