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 1359°C, 2478°F, 1632 K 
Period Boiling point 3230°C, 5846°F, 3503 K 
Block Density (g cm−3) 8.23 
Atomic number 65  Relative atomic mass 158.925  
State at 20°C Solid  Key isotopes 159Tb 
Electron configuration [Xe] 4f96s2  CAS number 7440-27-9 
ChemSpider ID 22397 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 abstracted compact disc symbol reflects the use of the element in the manufacture of the first rewritable compact discs.
A soft, silvery metal.
Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, all used in solid-state devices. It is also used in low-energy lightbulbs and mercury lamps. It has been used to improve the safety of medical x-rays by allowing the same quality image to be produced with a much shorter exposure time. Terbium salts are used in laser devices.

An alloy of terbium, dysprosium and iron lengthens and shortens in a magnetic field. This effect forms the basis of loudspeakers that sit on a flat surface, such as a window pane, which then acts as the speaker.
Biological role
Terbium has no known biological role. It has low toxicity.
Natural abundance
Terbium can be recovered from the minerals monazite and bastnaesite by ion exchange and solvent extraction. It is also obtained from euxenite, a complex oxide containing 1% or more of terbium.

The metal is usually produced commercially by reducing the anhydrous fluoride or chloride with calcium metal, under a vacuum. It is also possible to produce the metal by the electrolysis of terbium oxide in molten calcium chloride.
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Terbium was first isolated in 1843 by the Swedish chemist Carl Mosander at Stockholm. He had already investigated cerium oxide and separated a new element from it, lanthanum, and now he focussed his attention on yttrium, discovered in 1794, because he thought this too might harbour another element. In fact Mosander was able to obtain two other metal oxides from it: terbium oxide (yellow) and erbium oxide (rose pink) and these he announced in 1843. This was not the end of the story, however, because later that century these too yielded other rare earth elements (aka lanthanoids). Today these elements are easily separated by a process known as liquid-liquid extraction.

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) 2.33 Covalent radius (Å) 1.81
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 4, 3
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  159Tb 158.925 100


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) 55.7
Shear modulus (GPa) 22.1 Bulk modulus (GPa) 38.7
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - - 1.92
x 10-9
x 10-6
0.000988 0.0585 1.15 12.5 88 -
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Listen to Terbium Podcast
Transcript :

Chemistry in its element: terbium


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

(End promo)

Meera Senthilingam

This week a colourful element with a multitude of uses. Bringing you the luminous chemistry of terbium, here's Louise Natrajan.

Louise Natrajan

As a synthetic chemist whose job it is to study the chemistry of the lanthanide ions, I am often asked which one is my favourite. This is not however a particularly easy question to answer, and my reply often varies depending on which element I have been playing with in the lab that week. You see, although a common perception is that lanthanides all have the same chemistry, and some have even described them as 'boring', each element has its own unique and special characteristics.

Terbium, element number 65, is no different and lies in the middle of the lanthanide series in between gadolinium and dysprosium. It is one of the rarer rare earth elements, although it is still twice as common as silver in the Earth's crust. It is also one of the four lanthanide elements that are named after the place of its discovery, Ytterby in Sweden, 'the village of the four elements'. Terbium was first isolated after several of the other lanthanides in Stockholm, Sweden by Carl Gustav Mosander in 1843, who suspected that the mineral Yttria discovered previously in 1794 by Johan Gadolin might harbour other elements, just as ceria had done previously. Mosander was Professor of Chemistry and Mineralogy at the Karolinska Institute in Stockholm, and he succeeded in showing that yttria was mainly yttrium oxide, but also contained two other oxides, terbium oxide, which is yellow in colour and erbium oxide, which is a rose pink colour.

Compounds of terbium generally contain the terbium ion in its 3+ valence state, however in some solids, terbium is quite unusual in that it can exist in the 4+ valence state, due to the fact its fourth ionisation energy is relatively low so it attains a more stable half filled shell of electrons just as its neighbour gadolinium. The most striking property of terbium compounds comes from its spectroscopic and optical properties, which makes it one of the more exciting and studied lanthanide elements.

Terbium in the +3 state radiates an aesthetically pleasing luminous green colour when the correct wavelength of energy is used to excite the atoms. This is because terbium 3+ ions are strongly luminescent, so strong in fact, that its luminescence can often be seen by the naked eye The human eye is particularly sensitive to the colour green and even small amounts in the right compound are easily detectable by eye. This bright colour renders terbium compounds particularly useful as colour phosphors in lighting applications, e.g. in fluorescent lamps, where it is a yellow colour, and as with europium(III) which is red, provides one of the primary colours in TV screens; who knew that Tb could be in your TV set! Some terbium compounds are also quite unusual in that they display a phenomenon known as triboluminescence. This is a process where light is emitted when a crystalline solid compound is fractured, so a fracture in the crystalline lattice for example will result in the emission of bright green light that can be seen. The triboluminescence of Tb containing compounds can be exploited in fibre optic sensors that measure changes in mechanical stress e.g. pressure, strains, vibrations and acoustic emissions and has been proposed to be of use in monitoring structural stress in aeroplane wings!

Molecular terbium compounds have also found use in biological and medical research. The green emission of terbium compounds is very long lived, typically in the order of milliseconds, which means it can be detected long after the fluorescence of biological molecules has decayed away, and hence can be used as a biological probe to signal certain events. The luminescence from molecular Tb compounds can be switched on and off by chemical manipulations to the molecule and this has been exploited in the fabrication of sensors that measure the partial pressure of oxygen for example. Other Tb compounds have been used for the determination and quantification of drugs, in DNA and RNA assays, for the determination of protein structures and probes are currently being developed for in vitro cell imaging to aid in the early detection and treatment of diseases including cancer. Finally, Tb phosphors are also used as security inks and are found in anti counterfeit Euro bank notes, although europium is perhaps a little more famous for this role.

Besides its fantastic green colour, terbium also finds a niche role in its use in an alloy called Terfenol-D. Terfenol-D is an alloy of Tb, Fe and Dy and is a material that changes shape in a magnetic field; so called magnetostriction. It is used commercially in a speaker called the 'SoundBug', which turns any flat surface into a speaker! The device works by vibrating any material onto which it is placed such as a table or desk, making it into a speaker.

So what do TV screens, Euro bank notes, triboluminescence and SoundBug speakers all have in common? Terbium of course! So, now when someone asks me which lanthanide is my favourite, I'd have to say that terbium is definitely one of them and it is certainly far from being boring!

Meera Senthilingam

No, not boring at all if it helps make television, sound speakers and currency come into existence. That was Manchester University's Louise Natrajan explaining the many uses of terbium. Now next week a special treat, as we have an element that's so new that it hasn't even officially been named yet.

Sigurd Hofmann

In 1996 we set about producing element 112, inside a particle accelerator. We bombarded a lead target - that has 82 protons - with a zinc beam containing 30 protons for one week, and were able to detect a single atom of an element with 112 protons - element 112.

Meera Senthilingam

And Sigurd Hofmann, one of the discoverers of element 112 will be explaining the chemistry of this new element and also reveal what he and his team at the GSI Helmolt Centre for Heavy Ion Research in Germany are hoping to name it. So to find out, join us on next week's Chemistry in its Element. Until then I'm Meera Senthilingam from the and thank you for listening.


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

(End promo)
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Visual Elements images and videos
© Murray Robertson 2011.



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 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
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

© John Emsley 2012.



Produced by The Naked Scientists.


Periodic Table of Videos

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