Zinc – facts and properties
- Symbol
- Zn
- Atomic number
- 30
- Atomic mass
- 65.38 u
- Period
- 4
- Group
- 12
- Category
- metal
- Electron configuration
- [Ar] 3d¹⁰ 4s²
- Electronegativity
- 1.65
- Atomic radius
- 142 pm
- Valence electrons
- 12
- State at standard conditions
- solid
- Melting point
- 419.53 °C
- Boiling point
- 907 °C
- Density
- 7.134 g/cm³
- Discovered
- 1746
Zinc is a bluish-white metal with atomic number 30. It is used as a coating on crash barriers and fences, as the negative electrode in many batteries and as an ingredient of brass. The body needs it for numerous enzymes and for the immune system. Chemically, zinc stands slightly apart from the transition metals: it almost always forms Zn²⁺ ions with a charge of two plus and therefore mostly gives colourless compounds.
Position in the periodic table
Occurrence and extraction
Zinc occurs in nature only in compounds. The most important ore is sphalerite, a zinc sulfide, which is mined in Australia, China, Peru and India. There is also smithsonite, a zinc carbonate, once known as calamine, an old name for zinc carbonate ores.
Alloys containing zinc were known in antiquity: the Romans made brass by heating copper with calamine without knowing about the zinc itself. The reason is that zinc evaporates at high temperature and burns again at once in air. In England zinc was made on a larger scale from 1738. The Berlin chemist Andreas Sigismund Marggraf described in 1746 exactly how to obtain zinc from calamine and charcoal, and is therefore often regarded as its discoverer. The name probably derives from the German word Zinke, meaning prong, because zinc forms pointed, jagged crystals as it solidifies.
Today sphalerite is first roasted in air to give zinc oxide. The zinc oxide is dissolved in sulfuric acid, the solution is purified and the zinc is deposited at the cathode by electrolysis.
Properties and reactions
Zinc is in period 4 and group 12. Its electron configuration is [Ar] 3d¹⁰ 4s², so the d shell is completely filled. Zinc therefore gives up only its two outer electrons and almost always appears as zinc(II). Its electronegativity is 1.65. The metal has a density of 7.134 g/cm³, melts at 419.53 °C and boils at 907 °C. At room temperature zinc is rather brittle, but at roughly one hundred to one hundred and fifty degrees Celsius it can be rolled and shaped.
Zinc is a base metal. It dissolves in hydrochloric acid and dilute sulfuric acid, releasing hydrogen. Because zinc hydroxide is amphoteric, zinc also dissolves in strong alkalis, forming zincates. In air it is covered by a thin, firm layer of zinc oxide and zinc carbonate that protects the metal.
Zinc is much more reactive (less noble) than iron and lies above it in the reactivity series. If zinc is placed in a solution of a more noble metal salt, such as copper sulfate, the more noble metal is deposited while zinc goes into solution. The Daniell cell, a galvanic cell of zinc and copper, works on this principle.
Uses in everyday life and technology
About half of all zinc is used for corrosion protection. In hot-dip galvanising, steel parts are dipped into liquid zinc and become covered with a firm layer. Zinc protects twice over: as a barrier against oxygen and water and, if the layer is damaged, by cathodic protection. Because zinc is less noble than iron, the zinc is oxidised first when there is a scratch and the iron stays intact. With tinplate, which is coated with the more noble tin, the steel rusts faster after a scratch. The sacrificial anode uses the same principle: blocks of zinc are fixed to ship hulls and pipelines and dissolve in place of the steel.
Zinc is a component of brass and of many die-cast alloys. As sheet zinc it covers roofs and gutters. In batteries zinc serves as the negative electrode: zinc-carbon and alkaline batteries contain it as a metal powder or a cup. Zinc oxide is a white pigment used in skin ointments and sunscreen.
For humans, zinc is an essential trace element. It is part of many enzymes and important for wound healing, immune defence and growth. Meat, cheese, oats, pumpkin seeds and oysters are rich in zinc. Too much zinc from food supplements can do harm. Breathing in the fumes when welding galvanised parts can cause metal fume fever.
Molecules containing this element
- Zinc oxide ZnO
- Zinc sulfide ZnS
- Zinc chloride ZnCl2
Quick question
What do you observe for Zn + CuSO4(aq)?
FAQ
How does zinc protect against rust?
A layer of zinc keeps oxygen and water away from the steel. Even when it is scratched, zinc keeps protecting: it is less noble than iron and gives up its electrons first, so it corrodes instead of the iron. This is called cathodic corrosion protection.
What is a sacrificial anode?
A piece of base metal, usually zinc or magnesium, that is connected conductively to steel, for example on a ship hull or in a hot water tank. It corrodes in place of the steel and is used up in the process. Once it is used up, it has to be replaced.
What does the body need zinc for?
Zinc is a component of many enzymes and acts in the immune system, in wound healing and in cell growth. The body can hardly store it, so you need to take it in regularly from meat, cheese, oats or nuts. A deficiency shows up, among other things, as skin and hair problems and frequent infections.