Zinc

Zinc is the metal that protects the steel in your car, the lamp posts in your street and the corrugated roofs in developing countries from the damage of rust. It is also essential for your immune system, your wound healing and for hundreds of enzymes in your body to work properly.

  • Atomic Number3030 protons, 30 electrons
  • Atomic Mass65.4 uAbout 65× heavier than hydrogen
  • State at Room TempSolidbluish-white brittle metal
  • Density7.134 g/cm³Denser than iron but not by much
  • Melting / Boiling419.5°C / 906.9°CLow melting point at 420°C
  • Discovered1746Andreas Marggraf, 1746

Zinc is the last of the first-row transition metals. How does it compare?

Zinc closes out Period 4's transition metals, just beyond copper.

Atomic Mass Comparison
Nickel58.7 u
Copper63.5 u
Zinc65.4 u
Gallium69.7 u
Iron55.8 u

Zinc (65.4 u) is slightly heavier than copper (63.5 u) and nickel (58.7 u). It closes the first row of d-block transition metals and has a completely filled d subshell, which is why its chemistry is somewhat simpler and less colourful than the other transition metals.

What is zinc?

Zinc is a transition metal in Group 12 of the periodic table, though its chemistry is somewhat simpler than other transition metals because it has a completely filled d electron subshell. It has 30 protons and primarily exists in the +2 oxidation state. Zinc is a bluish-white metal that is brittle at room temperature but more malleable when moderately heated. It reacts readily with acids and more slowly with air, developing a thin protective layer of zinc carbonate.

Zinc gets its name from the German word Zinke, meaning tooth or spike, probably referring to the spiked appearance of zinc crystals. The element has been used for thousands of years in brass (a copper-zinc alloy), but pure zinc metal was not isolated in Europe until 1746 by the German chemist Andreas Marggraf, though Indian metallurgists had produced it centuries earlier. The symbol Zn comes from the name.

Fact Galvanising, coating steel with a thin layer of zinc to prevent rust, is one of the most important corrosion-prevention techniques in the world. Even when the zinc coating is scratched and the steel exposed, the zinc continues to protect the steel electrochemically, sacrificing itself by corroding first. This is why galvanised steel lasts decades rather than years.

Where you find zinc

On Earth

Zinc is the 24th most abundant element in the Earth's crust and one of the most widely mined metals after iron, aluminium and copper.

  • Sphalerite (ZnS). Zinc sulfide is by far the most important zinc ore. It is often found alongside lead ores. China, Peru, Australia and the USA are among the world's largest producers.
  • Smithsonite and hemimorphite. Zinc carbonate and zinc silicate minerals form in the weathered, oxidised zones of sulfide ore bodies and were historically the main zinc-smelting feedstock.

How we use zinc

  • Galvanising steel. About 50% of all zinc goes into galvanising, coating steel with zinc to prevent rust. Used in car bodies, street furniture, pylons, scaffolding, corrugated roofing sheets and thousands of other steel products.
  • Brass. Copper-zinc alloys (brasses) have been made since ancient times. Different proportions produce brasses with different properties, used in musical instruments, locks, taps, fittings and coins.
  • Batteries. The zinc-carbon and alkaline batteries in most AA and AAA cells have zinc as the negative electrode. Zinc-air batteries power many hearing aids.
  • Sun cream and medicine. Zinc oxide is a white mineral sunscreen that reflects UV light. Zinc compounds are used as antiseptics, in treating skin conditions, and as supplements for immune function and wound healing.
Did you know? Zinc is the second most abundant trace element in the human body after iron. It is found in more than 300 enzymes, including the ones that help you taste and smell, digest food, repair DNA and fight infection. Zinc deficiency, common in people with poor diets in developing countries, causes delayed growth, poor immune function and loss of the sense of smell and taste.

How it was discovered

Zinc smelting was practised in India by at least the 9th century CE: the ancient Indian city of Zawar contains the world's oldest known zinc smelting site, dating to around 1300 BCE. In China, zinc was produced from the 16th century. In Europe, Andreas Marggraf first isolated and characterised pure zinc in 1746, though brass (a zinc alloy) had been made in the Roman world from zinc-containing ores for centuries without understanding that zinc was a distinct metal.

Deeper dive: zinc in biology and galvanic corrosion

Zinc's role in biology is enormous and underappreciated. It is a structural component of "zinc finger" proteins, a type of protein domain that uses zinc ions to fold into a shape that can grip onto DNA. Zinc fingers are involved in regulating the expression of hundreds of genes. Many hormones, including insulin, are stored with zinc ions. The prostate gland contains particularly high concentrations of zinc, and zinc plays a role in male fertility.

The principle behind galvanising, "sacrificial protection", is a brilliant application of electrochemistry. When two different metals are electrically connected in the presence of moisture, the less noble metal (lower on the galvanic series) corrodes preferentially. Zinc is less noble than iron and corrodes first when the two are in contact. Even if the zinc coating is scratched and iron is exposed, the zinc around the scratch continues to corrode sacrificially, protecting the iron. Compare this to tin-plated cans: if tin is scratched, iron corrodes faster than if it were uncoated, because iron is less noble than tin.

Zinc also has an unusual property: it can be die-cast at relatively low temperatures, because its melting point (420°C) is lower than that of most structural metals. This makes zinc ideal for making complex, precise shapes cheaply, carburettors, door handles, toy cars and plumbing fittings are commonly die-cast in zinc alloys.

Zinc is the metal that prevents rust on a global scale and keeps your immune system running. Moving to 31 protons brings us to gallium, a metal so low-melting it can melt in your hand.