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 1072°C, 1962°F, 1345 K 
Period Boiling point 1794°C, 3261°F, 2067 K 
Block Density (g cm−3) 7.52 
Atomic number 62  Relative atomic mass 150.36  
State at 20°C Solid  Key isotopes 152Sm 
Electron configuration [Xe] 4f66s2  CAS number 7440-19-9 
ChemSpider ID 22391 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 mineral samarskite, from which samarium was first isolated, is named after Colonel Samarsky, a Russian mine official. The Soviet hammer, sickle and star are on a background that reflects the use of the element in lasers.
A silvery-white metal.
Samarium-cobalt magnets are much more powerful than iron magnets. They remain magnetic at high temperatures and so are used in microwave applications. They enabled the miniaturisation of electronic devices like headphones, and the development of personal stereos. However, neodymium magnets are now more commonly used instead.

Samarium is used to dope calcium chloride crystals for use in optical lasers. It is also used in infrared absorbing glass and as a neutron absorber in nuclear reactors. Samarium oxide finds specialised use in glass and ceramics. In common with other lanthanides, samarium is used in carbon arc lighting for studio lighting and projection.
Biological role
Samarium has no known biological role. It has low toxicity.
Natural abundance
Samarium is found along with other lanthanide metals in several minerals, the principal ones being monazite and bastnaesite. It is separated from the other components of the mineral by ion exchange and solvent extraction.

Recently, electrochemical deposition has been used to separate samarium from other lanthanides. A lithium citrate electrolyte is used, and a mercury electrode. Samarium metal can also be produced by reducing the oxide with barium.
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Samarium was one of the rare earths (aka lanthanoids) which perplexed and puzzled the chemists of the 1800s. Its history began with the discovery of cerium in 1803. This was suspected of harbouring other metals, and in 1839 Carl Mosander claimed to have obtained lanthanum and didymium from it. While he was right about lanthanum, he was wrong about didymium. In 1879, Paul-Émile Lecoq de Boisbaudran extracted didymium from the mineral samarskite. He then made a solution of didymium nitrate and added ammonium hydroxide. He observed that the precipitate which formed came down in two stages. He concentrated his attention on the first precipitate and measured its spectrum which revealed it to be a new element samarium. Samarium itself was eventually to yield other rare-earths: gadolinium in 1886 and europium in 1901.

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) 2.36 Covalent radius (Å) 1.85
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, 2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  144Sm 143.912 3.07
  147Sm 146.915 14.99 1.06 x 1011
  148Sm 147.915 11.24 7 x 1015
  149Sm 148.917 13.82 1016
  150Sm 149.917 7.38
  152Sm 151.920 26.75
  154Sm 153.922 22.75


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)
196 Young's modulus (GPa) 49.7
Shear modulus (GPa) 19.5 Bulk modulus (GPa) 37.8
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- 8.17
x 10-8
0.00221 0.942 51 - - - - - -
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Listen to Samarium Podcast
Transcript :

Chemistry in its element: samarium


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 rare, lustrous element with isotopes that have some unfathomably long half-lives. To tell us more, here's Richard Corfield:

Richard Corfield

Samarium is a rare earth element that - indirectly - has the distinction of being the first naturally occurring chemical element to be named after a living person. Samarium was isolated from the mineral Samarskite which was discovered near the small town of Miass in the southern Ural mountains in 1847. The mineral was named by the German Mineralogist Heinrich Rose after Vasili Evgrafovich Samarsky-Bykhovets, Chief of Staff of the Russian Corps of Mining Engineers between 1845 and 1861 who had given Rose the ore sample to study.

Although Samarium was discovered in 1853 by the Swiss chemist Jean Charles Galissard de Marignac - who first observed its sharp absorption lines in didymium - it was not until 1879 that it was isolated in Paris by the French chemist Paul Emile Lecoq de Boisbaudran using a sample from a newly located ore body in North Carolina.

Samarium is a rare earth metal with a pronounced silver lustre. It oxidizes in air and ignites spontaneously at 150 degrees centigrade. Rare Earth metals are a collection of seventeen chemical elements which include scandium, yttrium and fifteen lanthanoids. The term 'rare earth' is simple a reflection of the fact that these elements were originally isolated from uncommonly occurring oxide-type minerals. Today rare earth metals are increasingly important in the manufacture of high-tech electronic devices.

Samarium's geological origins in Samarskite is entirely in keeping with its importance to the science of geology. Samarium has several isotopes, four of which are stable and several of which are unstable. The half-lives of many of these are very short, on the order of a few seconds but three, 147Sm, 148Sm and 149Sm have extremely long half lives. It is 147Sm that is the key player in the sub-discipline of geology known as geochronology - the science of assigning absolute dates to minerals. 147Sm has a staggeringly long half life: 1.06x1011 years or, in real money, 106 billion years. Even by geological standards this gigantic figure is incomprehensible, especially if we remember that the Universe itself is only a little under fourteen billion years old. Thus one kg of 147Sm will decay to half a kilo of 147Sm in a period of time that is roughly eight times the duration of the Universe!

Given that the age of the Earth and the other planets of the solar system is only 4.5 billion years, why is this particular element and isotope so useful? Partly it is because the samarium to neodymium decay chain is highly resistant to metamorphosis, the geological process which transforms sedimentary and igneous rocks into other rock types by subjecting them to great heat or pressure or both. This has the effect of redistributing, or fractionating, the original elements. In the case of other geological chronometers, such as the uranium to lead or rubidium to strontium decay series this resets the decay chain clock, rendering them useless. Samarium to neodymium does not suffer from this disadvantage.

Samarium also has a long history in the nuclear industry. Soon after the Second World War the Indianapolis-based chemical giant Eli Lilley developed a fractional crystallisation technique for separating neodymium from ore. The synthesis of samarium and gadolinium was a by-product of the process and since 149Sm is a strong neutron absorber the product - called 'Lindsay Mix' - was sold as an early form of neutron damper for nuclear control rods. Even today samarium is still used as a neutron absorber in reactor control rods; particularly when mixed with europium and gadolinium forming the so-called samarium-europium-gadolinium (SEG) concentrate.

Samarium has more modest uses as well. These include its use as a component in carbon arc lights in the movie industry, as well as for making magnets that have a high resistance to demagnetisation. Such samarium-based magnets are perfect for both headphones as well as electric guitar pickups. Recently developed samarium/cobalt (SmCo5) magnets have the highest resistance to demagnetisation of any material yet synthesised.

Samarium oxide is also used in optical glass to absorb infrared radiation as well as to dope calcium fluoride crystals in optical lasers.

Samarium, like other rare earths is becoming progressively more valuable in a world whose dependence on high-technology is snow-balling. Recent reports have highlighted concerns that the Chinese are hoarding their native reserves of the rare earths to feed their electronic industries. This will certainly have the effect of hiking the price of samarium and the other rare earth elements so it may be time to consider buying share options. Not bad for an element first discovered in the mountains of tsarist Russia and which has - until now - been mostly noted for its arcane role in dating exotic rocks.

Meera Senthilingham

So get those samarium shares in ASAP. That was science writer Richard Corfield with the geological and technological uses of the element samarium. Now next week, we stick with the lanthanides and hear about an element that likes to play hard to get.

Simon Cotton

At that time, scientists were using improved techniques such as fractional crystallisation to obtain the individual lanthanides from mixtures. In 1886, Lecoq was the first person to identify dysprosium by separating its oxide from holmium oxide. It took him over 30 goes to do this, so he named the element accordingly, from the Greek word, dysprositos, meaning "hard to get at".

Meera Senthilingham

And Simon Cotton will be sharing some of the chemistry, properties and applications of dysprosium in next week's Chemistry in its Element. Until then, I'm Meera Senthilingham 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

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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.