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 11  Melting point Unknown 
Period Boiling point Unknown 
Block Density (g cm−3) Unknown 
Atomic number 111  Relative atomic mass [280]  
State at 20°C Solid  Key isotopes 280Rg 
Electron configuration [Rn] 5f146d107s1  CAS number 54386-24-2 
ChemSpider ID - 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
Roentgenium is named after Wilhelm Conrad Röntgen, the discoverer of x-rays. The image is based on an early x-ray tube. The background design is inspired by x-ray astronomy and particle accelerators.
A highly radioactive metal, of which only a few atoms have ever been made.
At present, it is only used in research.
Biological role
Roentgenium has no known biological role.
Natural abundance
A man-made element of which only a few atoms have ever been created. It is made by fusing nickel and bismuth atoms in a heavy ion accelerator.
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There are seven known isotopes of the element: 272, 274 and 278-282. The longest lived is isotope 281 which has a half-life of 22.8 seconds. In 1986, physicists at the Russian Joint Institute for Nuclear Research (JINR), bombarded bismuth with nickel hoping to make element 111, but they failed to detect any atoms of element 111. In 1994, a team led by Peter Armbruster and Gottfred Munzenberg at the German Geselleschaft für Schwerionenforschung (GSI), were successful when they bombarded bismuth with nickel and they obtained few atoms of isotope 272. It had a half-life of 1.5 milliseconds.

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) Unknown Covalent radius (Å) 1.21
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 Unknown
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  280Rg 280.165 - ~ 3.6 s  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 Roentgenium Podcast
Transcript :

Chemistry in its element: roentgenium


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 an element that needs just the right conditions in order to get a successful collision. Here's Simon Cotton:

Simon Cotton

I used to be able to go into my chemistry lab, look the pupils in the eye, and say 'U-U-U'. And they would say 'What have I done, Sir?' 'You've done nothing wrong' I would reply, 'I am talking about Element 111, unununium, symbol Uuu'.

So I was a bit sad when in 2004 a joint working party of the International Union of Pure and Applied Chemistry and International Union of Pure and Applied Physics recommended that the name of element 111 be changed to roentgenium, symbol Rg.

Roentgenium was in fact discovered 10 years earlier on December 8, 1994, by a team of 13 nuclear physicists working at the Gesellschaft für Schwerionenforschung at Darmstadt in Germany carried out an experiment, bombarding a target of 209Bi with 64Ni ions. The idea was to make the nickel ions penetrate the bismuth nucleus, so that the two nuclei would fuse together, making a bigger atom. The energy of the collision had to be carefully controlled, because if the nickel ions were not going fast enough, they could not overcome the repulsion between the two positive nuclei, would just fly off the bismuth on contact. However, if the nickel ions had too much energy, the resulting 'compound nucleus' would have so much excess energy that it could undergo fission and just fall apart. The trick was, like Goldilocks' porridge, to be 'just right', so that the fusion of the nuclei would occur, just.

Successful collisions would not occur very often, as most of an atom is empty space. The scientists were however able to observe three successful collisions, forming atoms of atomic number 111 and mass 272. They were very short-lived, with a half-life of around 1 ½ milliseconds. The new atoms were identified by following what happened to them when they decayed - they underwent alpha decay successively forming atoms of elements 109, 107, 105 and 103. In further experiments carried out in 2000, the team carried out more bombardments and observed another three more atoms of element 111. This time they followed the decay chains even further, right down to mendelevium-252, element 101.

The discovery of this new element was first announced in a paper published early in 1995. It was given a temporary name of unununium, derived from its atomic number, and the symbol Uuu. No permanent name was assigned to element 111, as independent confimation of its existence was needed, and this did not happen until 2003, when a team at the RIKEN Linear Accelerator facility in Japan made 14 atoms of this isotope. The workers at Darmstadt were then given the honor of proposing proposed the name roentgenium, in recognition of Wilhelm Conrad Roentgen, who discovered X-rays in 1895.

No one knows for sure what roentgenium looks like, but it has been placed under copper, silver and gold in the Periodic Table. Theoretical chemists have had fun predicting its properties, and they think that if anyone ever sees any roentgenium metal, it is likely to be silver in colour and it will be very unreactive. Its chemistry is predicted to involve the +3 and +5 oxidation states.

When scientists made element 115 back in 2004, they identified in its decay chain a roentgenium isotope of mass 280 with a half life of about 3.6 seconds. So if it can be made directly, there is the possibility of real chemical reactions being studied.

So, ladies and gentlemen, that is roentgenium, which looks like being a very precious metal, albeit only for a few seconds.

Meera Senthilingam

So blink and you may just miss the magic. That was Uppingham School's Simon Cotton with the speedy yet precise chemistry of roentgenium. Now next week we've got a two-faced element.

Tim Harrison

Chlorine is what you might describe as a Jekyll and Hyde element; it is the friend of the synthetic chemist and has found a use in a number of 'nice' applications such as the disinfecting of drinking water and keeping our swimming pools clean. It also has an unpleasant side, being the first chemical warfare agent and taking some of the blame for the depletion of the Earth's ozone layer.

Meera Senthilingam

So is it friend or is it foe? Join Bristol University's Tim Harrison to find out 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)
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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.