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 827°C, 1521°F, 1100 K 
Period Boiling point Unknown 
Block Density (g cm−3) Unknown 
Atomic number 101  Relative atomic mass [258]  
State at 20°C Solid  Key isotopes 258Md, 260Md 
Electron configuration [Rn] 5f137s2  CAS number 7440-11-1 
ChemSpider ID 22385 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 is inspired by, and based on, a photograph of Dimitri Mendeleev and an early version of the periodic table.
A radioactive metal, of which only a few atoms have ever been created.
Mendelevium is used only for research.
Biological role
Mendelevium has no known biological role.
Natural abundance
Mendelevium does not occur naturally. It is made by bombarding einsteinium with alpha particles (helium ions).
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Seventeen atoms of mendelevium were made in 1955 by Albert Ghiorso, Bernard Harvey, Gregory Chopin, Stanley Thompson, and Glenn Seaborg. They were produced during an all-night experiment using the cyclotron at Berkeley, California. In this, a sample of einsteinium-253 was bombarded with alpha-particles (helium nuclei) and mendelevium-256 was detected. This had a half-life of around 78 minutes. Further experiments yielded several thousand atoms of mendelevium, and today it is possible to produce millions of them. The longest lived isotope is mendelevium-260 which has a half-life of 28 days.

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) 2.46 Covalent radius (Å) 1.73
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
  258Md 258.098 - 51.5 d  α 
  260Md 260.104 - ~ 27.8 d  sf 


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.

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Listen to Mendelevium Podcast
Transcript :

Chemistry in its element: mendelevium


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 pays tribute to the creator of the periodic table. Here's Hayley Birch:

Hayley Birch

In 1933, Albert Einstein was visiting a friend at the University of California, Los Angeles, when he was introduced to an aspiring scientist by the name of Glenn Theodore Seaborg. Seaborg was studying chemistry and was only an undergraduate, but Einstein took the time to talk to him and encourage him in his scientific endeavours.

This meeting seems to have had a profound effect on the young Seaborg, who went on, like Einstein, to become a Nobel Prize winner and wrote in a tribute many years later that he had been much impressed by the great man's modesty and kindness. He also remarked upon Einstein's dedication to peace and was perhaps inspired by him in his own attitude to war. Despite playing a central role in the creation of the atomic bomb by helping to separate plutonium from uranium, he is said to have remained a pacifist and believed that nuclear energy should be used only for good.

By what appears to have been pure coincidence, it was on the day of Einstein's death - the 18 April 1955 - that the American Physical Society received a paper from Seaborg and his colleagues at the University of California, Berkeley, announcing the discovery of a new radioactive element that was to become known as mendelevium. At its most stable atomic weight of 258, it is considered one of the 'superheavy'-weights of the periodic table. Like most of the heavier elements, it's so large that it has trouble sticking itself together and usually decays after just a couple of hours - which is why Seaborg and his colleagues had to create it synthetically.

Considering his contribution to the Manhattan project, mendelevium was certainly not Seaborg's most significant achievement. It was not even his first element: he was part of a team based at the Radiation Laboratory that had already announced the discovery of americium and curium, as well as berkelium and californium, named after his own university. Four years previously he had been awarded the Nobel Prize, along with Edwin McMillan, for these very achievements, lumped together under what they called the trans-uranium elements - because they had atomic numbers higher than uranium.

At atomic number 101, mendelevium was a different type of element: the first of the trans-fermium elements. But to make it, Seaborg employed the same piece of equipment - the particle accelerator that had been used to chemically identify plutonium after it was discovered by Enrico Fermi during the Second World War. The '60-inch Cyclotron', as it was called, was built according to the design of Ernest Lawrence, another of Seaborg's colleagues from the Manhattan project, and had already been in operation for well over a decade. When it was finally decommissioned in 1962, it was hailed as the 'most productive atom-smasher in history'.

To make their synthetic element, Seaborg's team began with a tiny amount of another element, one which had first shown up in the fallout of a nuclear test carried out by the US in 1952. This other element was later to become einsteinium but it appears in the mendelevium paper as simply '99', accompanied by its isotope number, 253. The team used the cyclotron to smash helium ions into their 'element 99' and produce just a few atoms - 17, to be precise - of mendelevium. Even since its discovery, so little mendelevium has ever been produced that scientists haven't had a chance to find a use for it.

In the Physical Review paper announcing their discovery, Seaborg and his colleagues paid tribute to yet another great scientist. As they wrote: "We would like to suggest the name mendelevium... in recognition of the pioneering role of the great Russian chemist, Dmitri Mendeleev, who was the first to use the periodic system of the elements to predict the chemical properties of undiscovered elements."

And perhaps there is no more fitting time in this series to pay our own tribute to Mendeleev, who is, after all, the man responsible for the periodic table on which the Chemistry in its element podcast is based. 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.

And so, in mendelevium, Mendeleev got his element and, eventually, so did Seaborg, whom element 106 is named for.

Meera Senthilingham

So, both Mendeleev and Seaborg got their elements in the end. That was science writer Hayley Birch, bringing us the atom-smashing chemistry of mendelevium.

Now, next week, continuing along the lines of smashing atoms, we go one step further and experience elemental warfare.

Simon Cotton

In the days of the Cold War, America and Russia rivalled each other in all sorts of ways. Never mind thermonuclear bombs and intercontinental ballistic missiles to deliver them, they competed in putting men and women into space; who could win the most medals in the Olympic Games; and in making new chemical elements. In the case of element 105, the controversy went on for nearly 30 years and was part of the so-called 'Transfermium Wars', when no blood was spilt but a great deal of ink was.

In the Red corner, the Soviet team at the Joint Institute for Nuclear Research at Dubna, near Moscow, led by Georgy Flerov. In the Blue corner, the American team at the University of California at Berkeley, led by Albert Ghiorso.

Meera Senthilingham

And to find out which side came through with the chemistry (and name) of element 105, dubnium, join Simon Cotton for 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

(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.