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 Actinides  Melting point 860°C, 1580°F, 1133 K 
Period Boiling point Unknown 
Block Density (g cm−3) Unknown 
Atomic number 99  Relative atomic mass [252]  
State at 20°C Solid  Key isotopes 252Es 
Electron configuration [Rn] 5f117s2  CAS number 7429-92-7 
ChemSpider ID 22356 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 inspired by the work of Albert Einstein and images collected from early particle accelerators, such as those at Cern and Fermilab. The arrows are from one of these annotated (and unattributed) images indicating the direction of collisions. An abstracted ‘collider’ pattern is shown in the background.
A radioactive metal, only a few milligrams of which are made each year.
Einsteinium has no uses outside research.
Biological role
Einsteinium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Einsteinium can be obtained in milligram quantities from the neutron bombardment of plutonium in a nuclear reactor.
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Einsteinium was discovered in the debris of the first thermonuclear explosion which took place on a Pacific atoll, on 1 November 1952. Fall-out material, gathered from a neighbouring atoll, was sent to Berkeley, California, for analysis. There it was examined by Gregory Choppin, Stanley Thompson, Albert Ghiorso, and Bernard Harvey. Within a month they had discovered and identified 200 atoms of a new element, einsteinium, but it was not revealed until 1955.

The einsteinium had formed when some uranium atoms had captured several neutrons and gone through a series of capture and decay steps resulting in einsteinium-253, which has a half-life of 20.5 days.

By 1961, enough einsteinium had been collected to be visible to the naked eye, and weighed, although it amounted to mere 10 millionths of a gram.

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) 2.45 Covalent radius (Å) 1.65
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
  252Es 252.083 - 1.29 y  α 


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.



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)
Unknown 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)
- - - - - - - - - - -
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Listen to Einsteinium Podcast
Transcript :

Chemistry in its element: einsteinium


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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Meera Senthilingam

This week, there's no need to even guess who this element is named after, but it's more than fame that got this element its name - Brian Clegg

Brian Clegg

At first glance there's nothing odd about naming element 99 in the periodic table 'einsteinium'. After all, Einstein is the most famous scientist that has ever lived. Yet fame is not usually a good enough reason to make it into the exclusive club of the elements. Although the likes of Lawrence, Rutherford, Seaborg and Bohr have been honoured, there's no Newton or Laplace, Dalton or Feynman. Not even the new saint of science, Darwin.

The clue to Einstein's position here is that many of those with elements named after them played a fundamental role in our understanding of atomic structure. There is the odd highly doubtful case - but Einstein isn't one of them. He's not on the table because he's famous, but because he was responsible not only for relativity but for laying some of the foundations of quantum theory, which would explain how atoms interact. What's more, his study of Brownian motion was the first work to give serious weight to the idea that atoms existed at all.

For such a great figure, einsteinium verges on being an also-ran. It's one of the actinides, the second of the floating rows of the periodic table that are numerically squeezed between radium and lawrencium. Although only tiny amounts of it have ever been made, it's enough to determine that like its near neighbours in the table it is a silvery metal. Around twenty isotopes have been produced with half lives - that's the time it takes half of the substance to decay - ranging from seconds to over a year, though the most common isotope, einsteinium 253 only has a 20 day half life.

Apart from its name, what makes einsteinium stand out is the way it was first produced. When the Soviet Union developed its own atomic bomb, America felt it had to have something even more powerful to keep ahead. Using an atomic bomb as a trigger, the new type of device, referred to as a 'Super' would apply so much heat and pressure to the hydrogen isotope deuterium that the atoms would fuse together, just as they do in the Sun. It was to be the first thermonuclear weapon. The H bomb.

After months of technical testing of components, the first thermonuclear bomb was ready to be tried out at a remote island location, Elugelab on the Eniwetok Atoll in the South Pacific. Like the innocently named Little Boy and Fat Man - the bombs that were dropped on Hiroshima and Nagasaki - this bomb had a nickname. It was called 'the sausage' because of its long cylindrical shape.

When the bomb exploded on November the first, 1952, it produced an explosion with the power of over 10 million tonnes of TNT - five hundred times the destructive power of the Nagasaki explosion, totally destroying the tiny island. This was very much a test device - weighing over 80 tons and requiring a structure around 50 feet high to support it, meaning that it could never have been deployed - but it proved, all too well, the capability of the thermonuclear weapon. And in the moments of that intense explosion it produced a brand new element.

As part of the aftermath of the test, tonnes of material from the fallout zone were sent to Berkeley, the home of created elements, for testing. There among the ash and charred remains of coral were found a couple of hundred atoms of element 99, later to be called einsteinium. Such was the secrecy surrounding the test, the element's discovery was not made public for three years. It was in Physical Review of August the first 1955 that the discoverer Albert Ghiorso and his colleagues first suggested the name einsteinium.

In the intense heat and pressure of the explosion, some of the uranium in the fission bomb that was used to trigger the thermonuclear inferno had been bombarded with vast numbers of neutrons, producing a scattering of heavier atoms. At the same time, neutrons in the newly formed atoms' nuclei underwent beta decay, producing an electron and a proton. So instead of just getting heavier and heavier uranium isotopes, the result was an alchemist's delight of transmutation, ending up with einsteinium 253.

Not surprisingly, this production method is not the norm. Now, when einsteinium is required, plutonium is bombarded with neutrons in a reactor for several years until it is has taken on enough extra neutrons in the nucleus to pump it up to einsteinium. This only produces tiny amounts - in fact after its discovery it took a good 9 years before enough einsteinium had been produced to be able to see it.

In part the tiny quantities of einsteinium that have been made reflect the difficulty of producing it. But it also receives the sad accolade of having no known uses. There really isn't any reason for making einsteinium, except as a waypoint on the route to producing something else. It's an element without a role in life.

We started by thinking of why Einstein might be honoured by appearing in the periodic table. It's true that Albert Einstein made a huge contribution to the understanding of atoms and atomic structure. But it's hard not to see his presence in einsteinium being more because of the application of his iconic equation E=mc2 that he hated. The conversion of mass to energy in the world's most destructive weapons.

If Einstein can be considered the father of the nuclear explosion, then einsteinium will always be the child of the bomb.

Meera Senthilingam

That's quite a birth to come from an atomic bomb. That was Brian Clegg with the explosive origins of einsteinium. Now next week we've got a very useful element with many roles in life, including multiple ways of protecting our health.

Simon Cotton

It is also used in sunscreens, since it is a very opaque white and also very good at absorbing UV light. When UV light falls upon it, it generates free electrons that react with molecules on the surface, forming very reactive organic free radicals. Now you don't want these radicals on your skin, so the TiO2 used in sunscreens is coated with a protective layer of silica or alumina. In other situations, these radicals can be a good thing, as they can kill bacteria. You can put very thin coatings of TiO2 onto glass (or other substances like tiles); these are being tested in hospitals, as a way of reducing infections.

Meera Senthilingam

And Simon Cotton will be bringing us more of the uses and properties of titanium in next week's Chemistry in its element. Until then, I'm Meera Senthilingam 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.