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 Lanthanides  Melting point 822°C, 1512°F, 1095 K 
Period Boiling point 1529°C, 2784°F, 1802 K 
Block Density (g cm−3) 5.24 
Atomic number 63  Relative atomic mass 151.964  
State at 20°C Solid  Key isotopes 153Eu 
Electron configuration [Xe] 4f76s2  CAS number 7440-53-1 
ChemSpider ID 22417 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 design is based on the European Union flag and monetary symbol.
A soft, silvery metal that tarnishes quickly and reacts with water.
Europium is used in the printing of euro banknotes. It glows red under UV light, and forgeries can be detected by the lack of this red glow.

Low-energy light bulbs contain a little europium to give a more natural light, by balancing the blue (cold) light with a little red (warm) light.

Europium is excellent at absorbing neutrons, making it valuable in control rods for nuclear reactors.

Europium-doped plastic has been used as a laser material. It is also used in making thin super-conducting alloys.
Biological role
Europium has no known biological role. It has low toxicity.
Natural abundance
In common with other lanthanides, europium is mainly found in the minerals monazite and bastnaesite. It can be prepared from these minerals. However, the usual method of preparation is by heating europium(Ill) oxide with an excess of lanthanum under vacuum.
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Europium’s story is part of the complex history of the rare earths, aka lanthanoids. It began with cerium which was discovered in 1803. In 1839 Carl Mosander separated two other elements from it: lanthanum and one he called didymium which turned out to be a mixture of two rare earths, praseodymium and neodymium, as revealed by Karl Auer in 1879. Even so, it still harboured another rarer metal, samarium, separated by Paul-Émile Lecoq de Boisbaudran, and even that was impure. In 1886 Jean Charles Galissard de Marignac extracted gadolinium, from it, but that was still not the end of the story. In 1901, Eugène-Anatole Demarçay carried out a painstaking sequence of crystallisations of samarium magnesium nitrate, and separated yet another new element: europium.

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) 2.35 Covalent radius (Å) 1.83
Electron affinity (kJ mol−1) 83.363 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 3, 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  151Eu 150.920 47.81 > 1.7x1018
  153Eu 152.921 52.19


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 9.5
Crustal abundance (ppm) 0.3
Recycling rate (%) <10
Substitutability High
Production concentration (%) 97
Reserve distribution (%) 50
Top 3 producers
  • 1) China
  • 2) Russia
  • 3) Malaysia
Top 3 reserve holders
  • 1) China
  • 2) CIS Countries (inc. Russia)
  • 3) USA
Political stability of top producer 24.1
Political stability of top reserve holder 24.1


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)
182 Young's modulus (GPa) 18.2
Shear modulus (GPa) 7.9 Bulk modulus (GPa) 8.3
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- 1.74
x 10-5
0.109 19.4 - - - - - - -
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Listen to Europium Podcast
Transcript :

Chemistry in its element: europium


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, this week we're uncovering the origins of the element that put red into colour TV and also spawned a row with France, so I suppose there's nothing unusual there.

Brian Clegg

Many countries are honoured in the periodic table. There's americium, germanium, polonium, and francium, to name but a few. Usually these place names reflect where their discoverer worked. But despite the number of elements first isolated in England - ten were found at the Royal Institution in London alone - there is no Englandium, Unitedkingdium or Brittanium. However, there is europium, which allows for the possibility of a UK discoverer.

Europium is a lanthanide, one of those unfamiliar elements sitting outside the main structure of the periodic table. With atomic number 63, it inhabits the bar of elements that squeeze numerically between barium and hafnium. Along with scandium and yttrium, these are sometimes called rare earth elements - something of a misnomer, as they're not that scarce, but the minerals they were originally found in were rare, hence the name.

Europium wasn't so much discovered as groped towards. The British connection here is English scientist Sir William Crookes, who worked both in chemistry and physics. Crookes is probably best remembered for his work with discharge tubes. He was investigating (the scientific term for 'messing around with') the effect of putting a high voltage across two electrodes inside a tube with most of the air sucked out. This produced an unearthly glow on the glass at the end of the tube. Crookes called this effect a cathode ray. It was eventually shown to be caused by a stream of electrons, and the Crookes tube was the ancestor of traditional TV screens and computer monitors.

But Crookes was also an active chemist. He discovered the element thallium and is credited by some with the discovery of our topic today, europium. In the late 1880s, Crookes noticed a new line in spectroscopic analysis of a mineral containing ytterbium and samarium. Spectroscopy is a technique that makes it possible to analyze a material by measuring the different colours of light that are absorbed by it, or radiated when it's heated, giving a unique visual fingerprint. Crookes believed he had spotted a new element - so in a sense discovered europium, but never isolated it.

Others acknowledge French discoverers - either Paul Lecoq de Boisbaudran, a prolific investigator of new elements, who also identified a set of new lines a couple of years later, or definitively Eugene-Anatole Demarçay, who produced a europium salt in 1901 (it took many more years to get to the pure metal). It was certainly named by Demarçay - which should come as no surprise, as no Englishman of Crookes' time would think of himself as European.

This is a good example of the way that scientific discoveries aren't cut and dried. History-of-science expert Patricia Fara draws a parallel between the discoveries of europium and penicillin. We generally award the accolade for finding that life-saving mould to Alexander Fleming, who found it, but didn't pursue it further, rather than the team that isolated penicillin. But for europium, many historians play events the other way round, ignoring europium's Fleming, William Crookes.

Even if Crookes isn't the discoverer, he still plays a part in europium's story because of cathode ray tubes. If you are listening to this podcast on a computer with a traditional colour monitor, europium will be enhancing your view of the Chemistry World website. When colour TVs were first developed, the red pixels were relatively weak, which meant the whole colour spectrum had to be kept muted. But a phosphor doped with europium proved a much better, brighter source of red and is still present in most surviving monitors and TVs that predate the flat screen revolution.

Doping is something of a speciality for europium. Doping involves adding a relatively small amount of a material to another to change its properties. This is often europium's role in phosphors, the materials used to provide a glow when stimulated by electrons in TVs, or by ultraviolet in fluorescent lights. As well as the red glow from the valency three version of europium, its valency two salts produce a blue radiance. These are both combined with a third phosphor to produce white light in compact fluorescent bulbs.

Another phosphorescent role for europium, where the name is particularly apt, is as an anti-forgery mark on Euro bank notes. Europium is also behind the action of the mineral that gives us the word 'fluorescent'. In fluorescence, a material absorbs relatively high energy light such as ultraviolet and gives off a lower frequency in the visible range, making the substance unnaturally bright. The same type of europium responsible for the blue phosphor in fluorescent lights is present in some variants of the mineral fluorite, and it was its blue glow that resulted in the word fluorescent being derived from the mineral's name.

Although technically a metal, europium lacks the familiar metallic shininess because it oxidizes so easily. This silvery/white material is never naturally found in the free state. If it's not reacting with air, it fizzes away in water to produce a hydroxide. Europium is also a great neutron absorber, making it an interesting possibility for damping nuclear reactors by hoovering up stray neutrons, though it hasn't been widely used for this to date.

So that's europium - the substance that brings colours to phosphors. It's somehow rather appropriate that the discovery of europium, the element named after the continent of Europe, should be the subject of a dispute between England and France. Some things, it seems, will never change.

Chris Smith

Brian Clegg with the story of europium, the element that makes you see red, or at least it does on an old fashioned TV screen. Next week, the inside story on the element that just didn't want to be discovered.

Chris Orvig

Vanadium, a first row transition metal in the Periodic Table, is an element of mystery. Not only was it first transported two hundred years ago from Mexico, and lost in a shipwreck along with all of the relevant lab notes by the great German scientist Baron von Humboldt, but it required discovery several times by such famous names as Wöhler, Berzelius and del Rio (who was actually talked out of his claim in 1805).

Chris Smith

But why, and who did eventually discover vanadium and what do we do with it today. To find out join Chris Orvig, on next week's Chemistry in its element. I'm Chris Smith, thank you for listening and goodbye.


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.