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 1345°C, 2453°F, 1618 K 
Period Boiling point Unknown 
Block Density (g cm−3) 13.51 
Atomic number 96  Relative atomic mass [247]  
State at 20°C Solid  Key isotopes 243Cm, 248Cm 
Electron configuration [Rn] 5f76d17s2  CAS number 7440-51-9 
ChemSpider ID 22415 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 shows a satellite in orbit around the Earth, reflecting the use of curium in satellite technology.
A radioactive metal that is silver in colour. It tarnishes rapidly in air.
Curium has been used to provide power to electrical equipment used on space missions.
Biological role
Curium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Curium can be made in very small amounts by the neutron bombardment of plutonium in a nuclear reactor. Minute amounts may exist in natural deposits of uranium. Only a few grams are produced each year.
  Help text not available for this section currently


Curium was first made by the team of Glenn Seaborg, Ralph James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley, California. They bombarded a piece of the newly discovered element plutonium (isotope 239) with alpha-particles. This was then sent to the Metallurgical Laboratory at the University of Chicago where a tiny sample of curium was eventually separated and identified. However, news of the new element was not disclosed until after the end of World War II. Most unusually, it was first revealed by Seaborg when he appeared as the guest scientist on a radio show for children on 11 November 1945. It was officially announced the following week.

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) 2.450 Covalent radius (Å) 1.68
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
  243Cm 243.061 - 29.1 y  α 
        5.5 x 1011 sf 
  244Cm 244.063 - 18.1 y  α 
        1.32 x 107 sf 
  245Cm 245.065 - 8.48 x 103 α 
        1.4 x 1012 sf 
  246Cm 246.067 - 4.76 x 103 α 
        1.8 x 107 sf 
  247Cm 247.070 - 1.56 x 107 α 
  248Cm 248.072 - 3.48 x 105 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)
- - - 1.90
x 10-9
x 10-6
0.00103 0.0629 1.17 12.1 82.1 -
  Help text not available for this section currently


Listen to Curium Podcast
Transcript :

Chemistry in its element: curium


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's element launches us deep into outer space.

Richard Corfield

Curium is a member of a group of elements, the transuranic elements, that - with the exception of plutonium and neptunium - do not occur naturally on Earth. Curium is a hard, brittle, silvery radioactive metal that tarnishes slowly and which can only be produced in nuclear reactors. The isotope 242Cu was produced in 1944 by Glenn T Seaborg, Ralph A James and Albert Ghioso by bombarding 239Pu with alpha particles in the 60-inch Cyclotron at Berkeley University in the US. Like another synthetic element, americium, the discovery of curium was intimately bound up with the work of the Manhattan Project which Seaborg and his team were working on at the time of their discovery. This meant that neither curium nor americium could be announced to the world until after the end of the war. Seaborg revealed their discovery in November 1945 on the American TV show Quiz Kids just five days before the official unveiling of the new elements at a meeting of the American Chemical Society.

Curium is named in honour of Pierre and Marie Curie, who pioneered the study of radioactivity in the final days of the 19th century. Nineteen radioisotopes of curium are known to exist, the first of which, 242Cu was isolated in the hydroxide form in 1947 and in its elemental form in 1951. The most stable radioisotope is 247Cm which has a half-life of 1.56 × 107 years. 248Cm has a half-life of 3.40 × 105 years, 250Cm a half-life of 9000 years, and 245Cm a half-life of 8500 years. All of the remaining radioactive isotopes have half-lives with a duration that less than 30 years, and the majority of these have half-lives that are less than a month.

Curium has two main uses: as a fuel for Radioisotope Thermal Generators (RTGs) on board satellites, deep space probes, planetary surface rovers and in heart pacemakers, and as a alpha emitter for alpha particle X-Ray spectrometry, again particularly in space applications.

RTGs are electrical generators which produce power from radioactive decay. Usually heat released by the decay of a suitable radioactive material is converted into electricity by the Seebeck effect -where an electrical current is generated at the junctions between two different metals - using an array of thermocouples. However, in some cases such as the Mars Exploration Rovers, the power is used directly to warm the vehicle. For spaceflight use, the fuel must be radioactive enough to produce large quantities of energy per unit of mass and volume. 242Cu produces about 3W of heat energy from radioactive decay per gram which compares favourably with the plutonium and americium sources commonly used in other Radioisotope Thermal Generator applications.

Alpha Particle X-Ray Spectrometers (APXS) are devices that analyse the chemical element composition of a sample from back-scattered alpha particles. Using Rutherford's calculations of the conservation of nuclear energy and linear momentum it is possible to calculate the mass of the nucleus hit by the alpha particle and from this the energy spectrum of the material being analysed. Alpha Particle X-Ray Spectrometers tend to be confined to chemical analyses required during space missions since, although curium is both compact and power efficient, it is also a hazardous radioactive material. APXSs have a long history in space exploration being first used during the later Surveyor (Surveyor 5-7) missions that immediately preceded the Apollo Moon landings. Since the days of Surveyor alpha particle analysers have been included on many other missions including Mars Pathfinder, Mars 96, the Rosetta mission to the comet Comet 67 P/Churyumov- Gerasimenko and the Mars Exploration Rovers.

Back on Earth most curium found in the environment today was generated by the atmospheric testing of nuclear weapons, which ceased worldwide by 1980. More localised pockets of curium contamination have occurred through accidents at weapons production facilities.

As already mentioned, curium is hazardous. It becomes concentrated in bone marrow and because of its significant alpha activity can induce cancers. Despite its rarity and hazards it seems appropriate that an element first synthesised during a global conflict that saw the development of the vehicles that would one day take us to the Moon and beyond is now so pivotal to space exploration, providing our robotic pioneers not only with power but also the ability to analyse extraterrestrial materials as well.

Meera Senthilingam

So, a crucial element in the field of space exploration. That was science writer Richard Corfield bringing us the radio active chemistry of curium. Now next week, the element named after the creator of the periodic table.

Hayley Birch

Brought up in Russia, Mendeleev was the sort of person who, it seems, was incapable of sticking to one discipline and as well as serving as the director of the Russian institute for weights and measures, had a hand in developing the Russian oil industry. Given all this, it's perhaps less surprising than it ought to be that he conceived of the periodic table on the same day that he was supposed to be inspecting a cheese factory.

Meera Senthilingam

So, quite the multi tasker. And to find out the creation, chemistry and history of the Element named after Mendeleev, Mendelevium, join Hayley Birch 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

(End promo)
  Help text not available for this section currently
  Help Text


Learn Chemistry: Your single route to hundreds of free-to-access chemistry teaching resources.

Terms & Conditions

Images © Murray Robertson 1999-2011
Text © The Royal Society of Chemistry 1999-2011

Welcome to "A Visual Interpretation of The Table of Elements", the most striking version of the periodic table on the web. This Site has been carefully prepared for your visit, and we ask you to honour and agree to the following terms and conditions when using this Site.

Copyright of and ownership in the Images reside with Murray Robertson. The RSC has been granted the sole and exclusive right and licence to produce, publish and further license the Images.

The RSC maintains this Site for your information, education, communication, and personal entertainment. You may browse, download or print out one copy of the material displayed on the Site for your personal, non-commercial, non-public use, but you must retain all copyright and other proprietary notices contained on the materials. You may not further copy, alter, distribute or otherwise use any of the materials from this Site without the advance, written consent of the RSC. The images may not be posted on any website, shared in any disc library, image storage mechanism, network system or similar arrangement. Pornographic, defamatory, libellous, scandalous, fraudulent, immoral, infringing or otherwise unlawful use of the Images is, of course, prohibited.

If you wish to use the Images in a manner not permitted by these terms and conditions please contact the Publishing Services Department by email. If you are in any doubt, please ask.

Commercial use of the Images will be charged at a rate based on the particular use, prices on application. In such cases we would ask you to sign a Visual Elements licence agreement, tailored to the specific use you propose.

The RSC makes no representations whatsoever about the suitability of the information contained in the documents and related graphics published on this Site for any purpose. All such documents and related graphics are provided "as is" without any representation or endorsement made and warranty of any kind, whether expressed or implied, including but not limited to the implied warranties of fitness for a particular purpose, non-infringement, compatibility, security and accuracy.

In no event shall the RSC be liable for any damages including, without limitation, indirect or consequential damages, or any damages whatsoever arising from use or loss of use, data or profits, whether in action of contract, negligence or other tortious action, arising out of or in connection with the use of the material available from this Site. Nor shall the RSC be in any event liable for any damage to your computer equipment or software which may occur on account of your access to or use of the Site, or your downloading of materials, data, text, software, or images from the Site, whether caused by a virus, bug or otherwise.

We hope that you enjoy your visit to this Site. We welcome your feedback.


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.