Some elements exist in several different structural forms, called allotropes. Each allotrope has different physical properties.

For more information on the Visual Elements image see the Uses and properties section below.



A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.

A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.

Elements are organised into blocks by the orbital type in which the outer electrons are found. These blocks are named for the characteristic spectra they produce: sharp (s), principal (p), diffuse (d), and fundamental (f).

Atomic number
The number of protons in an atom.

Electron configuration
The arrangements of electrons above the last (closed shell) noble gas.

Melting point
The temperature at which the solid–liquid phase change occurs.

Boiling point
The temperature at which the liquid–gas phase change occurs.

The transition of a substance directly from the solid to the gas phase without passing through a liquid phase.

Density (g cm−3)
Density is the mass of a substance that would fill 1 cm3 at room temperature.

Relative atomic mass
The mass of an atom relative to that of carbon-12. This is approximately the sum of the number of protons and neutrons in the nucleus. Where more than one isotope exists, the value given is the abundance weighted average.

Atoms of the same element with different numbers of neutrons.

CAS number
The Chemical Abstracts Service registry number is a unique identifier of a particular chemical, designed to prevent confusion arising from different languages and naming systems.

Fact box

Group Melting point 1854°C, 3369°F, 2127 K 
Period Boiling point 4406°C, 7963°F, 4679 K 
Block Density (g cm−3) 6.52 
Atomic number 40  Relative atomic mass 91.224  
State at 20°C Solid  Key isotopes 90Zr, 92Zr, 94Zr 
Electron configuration [Kr] 4d25s2  CAS number 7440-67-7 
ChemSpider ID 22431 ChemSpider is a free chemical structure database


Image explanation

Murray Robertson is the artist behind the images which make up Visual Elements. This is where the artist explains his interpretation of the element and the science behind the picture.


The description of the element in its natural form.

Biological role

The role of the element in humans, animals and plants.

Natural abundance

Where the element is most commonly found in nature, and how it is sourced commercially.

Uses and properties

Image explanation
The Ancient Egyptians used zircon gemstones in jewellery. For the Ancient Egyptians the scarab beetle (represented here) was a symbol of regeneration and creation, conveying ideas of transformation, renewal and resurrection.
A hard, silvery metal that is very resistant to corrosion.
Zirconium does not absorb neutrons, making it an ideal material for use in nuclear power stations. More than 90% of zirconium is used in this way. Nuclear reactors can have more than 100,000 metres of zirconium alloy tubing. With niobium, zirconium is superconductive at low temperatures and is used to make superconducting magnets.

Zirconium metal is protected by a thin oxide layer making it exceptionally resistant to corrosion by acids, alkalis and seawater. For this reason it is extensively used by the chemical industry.

Zirconium(IV) oxide is used in ultra-strong ceramics. It is used to make crucibles that will withstand heat-shock, furnace linings, foundry bricks, abrasives and by the glass and ceramics industries. It is so strong that even scissors and knives can be made from it. It is also used in cosmetics, antiperspirants, food packaging and to make microwave filters.

Zircon is a natural semi-precious gemstone found in a variety of colours. The most desirable have a golden hue. The element was first discovered in this form, resulting in its name. Cubic zirconia (zirconium oxide) is a synthetic gemstone. The colourless stones, when cut, resemble diamonds.

Zircon mixed with vanadium or praseodymium makes blue and yellow pigments for glazing pottery.
Biological role
Zirconium has no known biological role. It has low toxicity.
Natural abundance
Zirconium occurs in about 30 mineral species, the major ones being zircon and baddeleyite. More than 1.5 million tonnes of zircon are mined each year, mainly in Australia and South Africa. Most baddeleyite is mined in Brazil.

Zirconium metal is produced commercially by first converting zircon to zirconium chloride, and then reducing the chloride with magnesium.
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Gems that contain zirconium were known in ancient times as zircon. In 1789, the German chemist, Martin Klaproth analysed a zircon and separated zirconium in the form of its ‘earth’ zirconia, which is the oxide ZrO2.

Klaproth failed to isolate the pure metal itself, and Humphry Davy also failed when he tried electrolysis in 1808. It was not until 1824 that the element was isolated, when the Swedish chemist Jöns Berzelius heated potassium hexafluorozirconate (K2ZrF6) with potassium metal and obtained some zirconium as a black powder.

Totally pure zirconium was only produced in 1925 by the Dutch chemists Anton Eduard van Arkel and Jan Hendrik de Boer by the decomposition of zirconium tetraiodide (ZrI4). These days the metal is produced in bulk by heating zirconium tetrachloride (ZrCl4) with magnesium.

Atomic radius, non-bonded
Half of the distance between two unbonded atoms of the same element when the electrostatic forces are balanced. These values were determined using several different methods.

Covalent radius
Half of the distance between two atoms within a single covalent bond. Values are given for typical oxidation number and coordination.

Electron affinity
The energy released when an electron is added to the neutral atom and a negative ion is formed.

Electronegativity (Pauling scale)
The tendency of an atom to attract electrons towards itself, expressed on a relative scale.

First ionisation energy
The minimum energy required to remove an electron from a neutral atom in its ground state.

Atomic data

Atomic radius, non-bonded (Å) 2.23 Covalent radius (Å) 1.64
Electron affinity (kJ mol−1) 41.103 Electronegativity
(Pauling scale)
Ionisation energies
(kJ mol−1)


Common oxidation states

The oxidation state of an atom is a measure of the degree of oxidation of an atom. It is defined as being the charge that an atom would have if all bonds were ionic. Uncombined elements have an oxidation state of 0. The sum of the oxidation states within a compound or ion must equal the overall charge.


Atoms of the same element with different numbers of neutrons.

Key for isotopes

Half life
  y years
  d days
  h hours
  m minutes
  s seconds
Mode of decay
  α alpha particle emission
  β negative beta (electron) emission
  β+ positron emission
  EC orbital electron capture
  sf spontaneous fission
  ββ double beta emission
  ECEC double orbital electron capture

Oxidation states and isotopes

Common oxidation states 4
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  90Zr 89.905 51.45
  91Zr 90.906 11.22
  92Zr 91.905 17.15
  94Zr 93.906 17.38 > 1017 β-β- 
  96Zr 95.908 2.8 2.3 x 1019 β-β- 
        > 1.7 x18 β- 


Data for this section been provided by the British Geological Survey.

Relative supply risk

An integrated supply risk index from 1 (very low risk) to 10 (very high risk). This is calculated by combining the scores for crustal abundance, reserve distribution, production concentration, substitutability, recycling rate and political stability scores.

Crustal abundance (ppm)

The number of atoms of the element per 1 million atoms of the Earth’s crust.

Recycling rate

The percentage of a commodity which is recycled. A higher recycling rate may reduce risk to supply.


The availability of suitable substitutes for a given commodity.
High = substitution not possible or very difficult.
Medium = substitution is possible but there may be an economic and/or performance impact
Low = substitution is possible with little or no economic and/or performance impact

Production concentration

The percentage of an element produced in the top producing country. The higher the value, the larger risk there is to supply.

Reserve distribution

The percentage of the world reserves located in the country with the largest reserves. The higher the value, the larger risk there is to supply.

Political stability of top producer

A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.

Political stability of top reserve holder

A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators.

Supply risk

Relative supply risk 5.7
Crustal abundance (ppm) 132
Recycling rate (%) <10
Substitutability Unknown
Production concentration (%) 39
Reserve distribution (%) 40
Top 3 producers
  • 1) Australia
  • 2) South Africa
  • 3) China
Top 3 reserve holders
  • 1) Australia
  • 2) South Africa
  • 3) Ukraine
Political stability of top producer 74.5
Political stability of top reserve holder 74.5


Specific heat capacity (J kg−1 K−1)

Specific heat capacity is the amount of energy needed to change the temperature of a kilogram of a substance by 1 K.

Young's modulus

A measure of the stiffness of a substance. It provides a measure of how difficult it is to extend a material, with a value given by the ratio of tensile strength to tensile strain.

Shear modulus

A measure of how difficult it is to deform a material. It is given by the ratio of the shear stress to the shear strain.

Bulk modulus

A measure of how difficult it is to compress a substance. It is given by the ratio of the pressure on a body to the fractional decrease in volume.

Vapour pressure

A measure of the propensity of a substance to evaporate. It is defined as the equilibrium pressure exerted by the gas produced above a substance in a closed system.

Pressure and temperature data – advanced

Specific heat capacity
(J kg−1 K−1)
278 Young's modulus (GPa) Unknown
Shear modulus (GPa) Unknown Bulk modulus (GPa) Unknown
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - - - 1.05
x 10-10
x 10-8
x 10-6
0.00045 0.011 0.155
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Listen to Zirconium Podcast
Transcript :

Chemistry in its element: zirconium


You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

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Chris Smith

Hello and welcome to our tour of the unusual, exciting and deadly aspects of the elements that make up the world around us. We're kicking off our journey through the Periodic Table with a chemical that sometimes masquerades as diamond but is equally at home in the core of a nuclear reactor or even in an ironworks. To tell the story of this mysterious entity which is otherwise known as zirconium, here's chemist and award winning author John Emsley.

John Emsley

Zirconium. Wear it flashing on your finger, or unseen within your frame, it holds the key to nuclear energy, and it's got a gem-like name. It's zirconium.

The name zirconium comes from the Arabic word zargun which refers to a golden-hued gemstone known since Biblical times called zircon. Today artificial gems are made from Zirconium oxide known as cubic zirconia and they sparkle with more brilliance than diamond although they are not as hard. What distinguishes them from real diamond is their higher density of 6.0 g cm-3 compared to diamond's 3.52.

Zirconium is abundant in S-type stars in which heavier elements are formed by neutron capture. Traces are also present in the Sun. Rock brought back from the moon was found to have a surprisingly high zirconium content. Down here on Earth zircons has shown that life might have started much earlier than once thought. These were found in Australia in the year 2000 were 4.4 billion years old, and their oxygen isotope ratio of O16/O18 showed they could only have been formed when there was liquid water on the surface of the Earth, and this was nearly 500 million years earlier than previously assumed.

In the Middle Ages colourless gemstones of zircon were thought to be an inferior kind of diamond, but that was shown to be wrong when a German chemist, Martin Klaproth (1743-1817), analysed one in 1789 and discovered zirconium. Klaproth was unable to isolate the metal itself. That was achieved in 1824 by the Swedish chemist Jöns Jacob Berzelius but there was little use for it or its chemical compounds, and so it languished for a century or more.

Today this element is widely used, as zircon, as Zirconium oxide and as the metal itself. Zirconium is to be found in ceramics, foundry equipment, glass, chemicals, and metal alloys.

Zircon sand is used for heat-resistant linings for furnaces, for giant ladles for molten metal, and to make foundry moulds. Mixed with vanadium or praseodymium zircon makes blue and yellow pigments for glazing pottery and tiles.

Zirconium oxide is used to make heat resistant crucibles, ceramics and abrasives. A red-hot crucible made from it can be plunged into cold water without cracking. Zirconium oxide is to be found in ultra-strong ceramics that are stronger and sharper even than toughened steel and are used for knives, scissors and golf irons. Production of pure zirconium oxide is almost 25 000 tons per year, and it also goes into various chemicals that end up as cosmetics, antiperspirants, food packaging, and even fake gems. The paper and packaging industry is finding zirconium compounds make good surface coatings because they have excellent water resistance and strength. Equally important is their low toxicity.

Zirconium metal has an oxidised surface which is both hard and impervious to chemical attack making it ideal not only for chemical plants but for body implants such as hip replacement joints. Zirconium-aluminium alloy is used for top of the range bicycle frames because it combines strength and lightness.

Zirconium metal had some hidden assets which suddenly brought it to prominence in the late 1940s; it was found to be the ideal metal for inside nuclear reactors and nuclear submarines. It does not corrode at high temperatures, nor absorb neutrons to form radioactive isotopes. Even today the nuclear industry buys almost all of the metal that is produced and some nuclear reactors have more than 100 kilometres of zirconium tubing. Zirconium is used to make the cladding for uranium oxide fuel elements. As mined, zirconium contains 1-3% per cent of hafnium, which is chemically very similar, and although it is difficult to separate the two elements this has to be done for the metal used in the nuclear industry because hafnium absorbs neutrons very strongly.

Finally, we have two zirconium materials with extreme properties, one which it displays when very cold, the other when it is heated to high temperatures. The first is a zirconium-niobium alloy which becomes superconducting below 35 Kelvin (- 238oC) in other words it will conduct electricity with no loss of energy. The second is zirconium tungstate (ZrW2O8) which actually shrinks as you heat it up, at least until it reaches 700oC when it decomposes into the two metal oxides.

Chris Smith

John Emsley unlocking the secrets of element number 40, zirconium. And you can find out some more about John's favourite elements in a series he has written for the RSC's Education in Chemistry which is online at Next time on Chemistry in its Element, life's a gas with Mark Peplow.

Mark Peplow

Little did those humble cyanobacteria realize what they were doing when two and a half billion years ago, they started to build up their own reserves of energy-rich chemicals, by combining water and carbon dioxide. Powered by sunlight, they spent the next two billion years terraforming our entire planet with the waste product of their photosynthesis, a rather toxic gas called oxygen.

Chris Smith

So join us next week for a breath of fresh air and the story of oxygen. I'm Chris Smith, thanks for listening, see you next time.


Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by There's more information and other episodes of Chemistry in its element on our website at

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Visual Elements images and videos
© Murray Robertson 1998-2017.



W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, CRC Press/Taylor and Francis, Boca Raton, FL, 95th Edition, Internet Version 2015, accessed December 2014.
Tables of Physical & Chemical Constants, Kaye & Laby Online, 16th edition, 1995. Version 1.0 (2005), accessed December 2014.
J. S. Coursey, D. J. Schwab, J. J. Tsai, and R. A. Dragoset, Atomic Weights and Isotopic Compositions (version 4.1), 2015, National Institute of Standards and Technology, Gaithersburg, MD, accessed November 2016.
T. L. Cottrell, The Strengths of Chemical Bonds, Butterworth, London, 1954.


Uses and properties

John Emsley, Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, New York, 2nd Edition, 2011.
Thomas Jefferson National Accelerator Facility - Office of Science Education, It’s Elemental - The Periodic Table of Elements, accessed December 2014.
Periodic Table of Videos, accessed December 2014.


Supply risk data

Derived in part from material provided by the British Geological Survey © NERC.


History text

Elements 1-112, 114, 116 and 117 © John Emsley 2012. Elements 113, 115, 117 and 118 © Royal Society of Chemistry 2017.



Produced by The Naked Scientists.


Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.