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 1529°C, 2784°F, 1802 K 
Period Boiling point 2868°C, 5194°F, 3141 K 
Block Density (g cm−3) 9.07 
Atomic number 68  Relative atomic mass 167.259  
State at 20°C Solid  Key isotopes 166Er 
Electron configuration [Xe] 4f126s2  CAS number 7440-52-0 
ChemSpider ID 22416 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 image reflects the use of the element in producing pink glazes in ceramics.
A soft, silvery metallic element.
Erbium finds little use as a metal because it slowly tarnishes in air and is attacked by water.

When alloyed with metals such as vanadium, erbium lowers their hardness and improves their workability.

Erbium oxide is occasionally used in infrared absorbing glass, for example safety glasses for welders and metal workers. When erbium is added to glass it gives the glass a pink tinge. It is used to give colour to some sunglasses and imitation gems.

Broadband signals, carried by fibre optic cables, are amplified by including erbium in the glass fibre.
Biological role
Erbium has no known biological role, and has low toxicity.
Natural abundance
Erbium is found principally in the minerals monazite and bastnaesite. It can be extracted by ion exchange and solvent extraction.
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In 1843, at Stockholm, Carl Mosander obtained two new metal oxides from yttrium, which had been know since 1794. One of these was erbium oxide, which was pink. (The other was terbium oxide, which was yellow.) While erbium was one of the first lanthanoid elements to be discovered, the picture is clouded because early samples of this element must have contained other rare-earths. We know this because In1878 Jean-Charles Galissard de Marignac, working at the University of Geneva, extracted another element from erbium and called it ytterbium. (This too was impure and scandium was extracted from it a year later.)

A sample of pure erbium metal was not produced until 1934, when Wilhelm Klemm and Heinrich Bommer achieved it by heating purified erbium chloride with potassium.

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) 2.29 Covalent radius (Å) 1.77
Electron affinity (kJ mol−1) Unknown 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
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  162Er 161.929 0.139
  164Er 163.929 1.601
  166Er 165.930 33.503
  167Er 166.932 22.869
  168Er 167.932 26.978
  170Er 169.935 14.91


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)
168 Young's modulus (GPa) 69.9
Shear modulus (GPa) 28.3 Bulk modulus (GPa) 44.4
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - 3.90
x 10-10
x 10-6
0.00205 0.163 4.23 52.5 - - -
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Listen to Erbium Podcast
Transcript :

Chemistry in its element: erbium


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

(End promo)

Chris Smith

This week we meet the man and one of the chemicals that led to the birth of the science of spectroscopy, but is pink your colour?

Andrea Sella

A couple of years ago a colleague popped his head round my door and said, as chemists do, "I'm on the scrounge". It's quite common in chemistry departments - you want to do a quick experiment and just want a smidge of something without having to order a whole bottle. So you ask a friend whether they have a bit of whatever. "Have you got some erbium oxide?" "Sure I said. I've got some up in the lab". A few minutes later my friend went off with a small bottle containing a delicate pink coloured powder.

A few weeks later I saw him in the stairwell and asked him how he'd got on with the erbium. "It's amazing stuff. You HAVE to see this." He replied. He pulled out of his pocket a sample vial containing some stunning pink crystals that glinted alluringly. "Wow!" I said - chemists are always impressed by nice crystalline products. "It gets better." he said mysteriously. He beckoned me into a hallway that had recently been refurbished. "Look" he said.

As the crystals caught the light from the new fluorescent lights hanging from the ceiling, the pink colour seemed to deepen and brighten up. "Wow!" I said again. We moved the crystals back into the sunlight and the colour faded again. Moving the crystals back and forth they glowed and dimmed in magical fashion.

It was a stunning example of the luminescence of the group of elements, the rare earths, of which erbium is a member. The red phosphor in the fluorescent lights must have contained erbium ions and because the emission wavelength of the phosphor exactly matched the absorption in my friend's crystals, resonant absorption occurs causing the magical glow.

The rare earths were revealed to the world quite by accident by a Swedish lieutenant and rock-hound Carl Axel Arrhenius in 1787 in a quarry on the island of Vaxholm in Sweden, where the small town of Ytterby is located. The mineral that Arrhenius had discovered would lead to the discovery of 16 elements, all of them with remarkably similar properties. And the small village of Ytterby would provide the inspiration for the names of several of them: ytterbium, yttrium, terbium, and the element of this podcast, erbium. Others got names like scandium, holmium, thulium in recognition of the region whence they first appeared.

For over a century, controversy raged amongst chemists about these elements. And one of the key players in this chemical row was Robert Bunsen, the co-inventor with Gustav Kirchoff, of spectroscopy. Together they had had the idea of putting chemical compounds into a flame and analyzing the resulting light with a prism. The spectra they observed proved to be amazing analytical tools - Kirchoff would use the method to identify elements on the sun. The method rapidly became one of the central pillars of chemistry.

But like many others working in the area, Bunsen was intrigued by the faint colours of the lanthanides, and their remarkable invariance. Erbium compounds, regardless of the partner - the oxide, the chloride, fluoride, amide, hydrocarbyls - are almost invariably faint pink. Over a period of three long years Bunsen methodically carried out the hundreds of crystallizations need to purify the elements, and then meticulously measured and sketched the spark spectra which contained many sharp bands of varying intensities. It was a spectroscopic tour de force for its time. At last, in May 1874, Bunsen finished writing his monumental manuscript. With a feeling of relief, he finally headed off to the local pub for lunch.

Imagine the poor man's horror when he got back to the lab and the manuscript was gone. A round bottom flask of water on the desk had focussed the spring sunshine from the window and set fire to the entire pile. Years of work reduced to ashes. After venting his despair in a couple of letters to friends, Bunsen painstakingly redid the work from scratch, laying the foundation of our understanding of the electronic structures of elements such as erbium.

We now realize that the valence electrons of erbium - of which there are 11 in its compounds, are buried deep within the core of the atom. Their location makes them remarkably insensitive to the world outside - which is why the colours are so consistent from compound to compound.

But what Bunsen could not know, was that there were spectroscopic bands in the infrared part of the spectrum and it is these that are what makes erbium so valuable to us today. As you are probably aware, most of our telephone calls and internet data transfers are carried by optical fibres. These gossamer thin threads of glass are of a rare optical perfection. But much like light passing through the atmosphere, scattering occurs - photons of light collide occasionally with the chains of glass in the fibre and the light is attenuated, limiting the length of fibre one can use. This phenomenon, called Rayleigh scattering, is the same that causes the daytime sky to be blue and sunsets to be red. The shorter the wavelength, the greater the scattering. Erbium light - at 1.55 microns, in the near infrared region of the spectrum - falls right where Rayleigh scattering is at a minimum but away from where bond vibrations of the glass absorb infrared light. Erbium lasers and amplifiers are therefore the hub around which all of our modern telecommunications revolve. So the next time you phone a friend and say to them "It's a lovely day. Let's go to the park", think Erbium. It may only be the 44th most abundant element on our planet. But it punches far above its weight.

Chris Smith

How ironic that the man who invented the Bunsen burner ended up with his work going up in smoke thanks to the sun. That was UCL chemist, Andrea Sella telling the story of Robert Bunsen and the element Erbium. Next time to the philosopher's stone and the man who boiled up urine expecting to get gold, and found this element instead.

Nina Notman

Phosphorus was first made by Hennig Brandt in Hamburg in Germany in 1669 when he evaporated urine and heated the residue until it was red hot. Glowing phosphorus vapour came off and he condensed it under water. And for more than 100 years most phosphorus was made this way. This was until people realised that bone was a great source of phosphorus. Bone can be dissolved in sulfuric acid to form phosphoric acid, which is then heated with charcoal to form white phosphorus.

Chris Smith

But what can we do with it? You can find out next time when Nina Notman tells the tale of Phosphorous on next week's Chemistry in its Element, I hope you can join us. 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.