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 986°C, 1807°F, 1259 K 
Period Boiling point Unknown 
Block Density (g cm−3) 14.78 
Atomic number 97  Relative atomic mass [247]  
State at 20°C Solid  Key isotopes 247Bk, 249Bk 
Electron configuration [Rn] 5f97s2  CAS number 7440-40-6 
ChemSpider ID 22409 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
An abstract metal symbol is against a background of vibrant colours representing the creation of the element in nuclear reactors.
Berkelium is a radioactive, silvery metal.
Because it is so rare, berkelium has no commercial or technological use at present.
Biological role
Berkelium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Less than a gram of berkelium is made each year. It is made in nuclear reactors by the neutron bombardment of plutonium-239.
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Berkelium was first produced in December 1949, at the University of California at Berkeley, and was made by Stanley Thompson, Albert Ghiorso, and Glenn Seaborg. They took americium-241, which had first been made in 1944, and bombarded it with helium nuclei (alpha particles) for several hours in the 60-inch cyclotron. The americium itself had been produced by bombarding plutonium with neutrons.

The Berkeley team dissolved the target in acid and used ion exchange to separate the new elements that had been created. This was the isotope berkelium-243 which has a half-life of about 5 hours. It took a further nine years before enough berkelium had been made to see with the naked eye, and even this was only a few micrograms. The first chemical compound, berkelium dioxide, BkO2, was made in 1962.

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) 2.44 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
  247Bk 247.070 - 1.43 x 103 α 
  249Bk 249.075 - 320 d  β 
        1.8 x 109 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.

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 Berkelium Podcast
Transcript :

Chemistry in its element: berkelium


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, no prizes for guessing where this element's name comes from. Eric Scerri.

Eric Scerri

Element 97 in the periodic table is one of only two elements named after a university, namely the University of California at Berkeley. The other such element is number 110 called darmstadtium after the University of Darmstadt in Germany. The university and the city of Berkeley were in turn named after the Anglo-Irish philosopher, Bishop George 'Barkeley'. The pronunciation changed from Barkeley to Berkeley when the name crossed the Atlantic ocean in 1869, the year that the city and university were both founded. Incidentally this was the same year in which Dimitri Mendeleev published the first mature periodic system and began to predict the existence of new elements.

But let me get back to berkelium. It was the fifth element in the periodic table after the last naturally occurring element, uranium, to be artificially synthesised. Berkelium was first made some 60 years ago by Stan Thomson, Al Ghiroso and Glen Seaborg by bombarding the isotope americium-241 with alpha particles. The half-life of the first isotope of berkelium to be produced in this way was a healthy 4.5 hours. Subsequently discovered isotopes have included berkelium-249 with a half-life of as much as 314 days.

One of the discoverers, Glen Seaborg, was a member of various teams that synthesised a total of 10 elements over a period of many years. His success led to a proposal that he should have an element named after him. But the official governing body, the International Union of Pure and Applied Chemistry, refused to accept this, on the basis that no living scientist had ever been honoured in this way, although actually the element fermium was proposed when the Italian physicist Enrico Fermi was still living and was indeed accepted.

Finally after much campaigning by chemists around the world, IUPAC relented and element 106 was duly named seaborgium while he was still alive. This led to an amusing situation whereby people could try to send letters or postcards to Seaborg by using nothing but a sequence of symbols of various elements in the following order. First of all one could write Sg for element 106 or Seaborg's name. The second line consisted of Bk for this week's element 97 or the University at which Seaborg worked. The third line was Cf for element 98, or californium, or the state in which the university stands. Finally, if writing from abroad, the correspondent could add Am for element 95, or americium, or the country of America to complete the address.

To the credit of several postal systems around the world a handful of people did indeed succeed in getting letters and messages of congratulations to Seaborg in this cryptic fashion.

Many compounds of element 97, berkelium, have been prepared. Unlike the extremely short half-lives possessed by the superheavy elements like 117 and 118 that have been in the news recently, experiments on berkelium are relatively easy to perform and its chemistry has been studied in some detail.

The existence of weighable amounts of berkelium-249 have made it possible to determine some of its properties using macroscopic quantities. Although the pure element has not yet been isolated, it is predicted to be a silvery metal that would easily oxidise in air at high temperatures and would be soluble in dilute mineral acids.

X-ray diffraction techniques have been used to identify various berkelium compounds such as berkelium dioxide (BkO2), berkelium fluoride (BkF3), berkelium oxychloride (BkOCl), and berkelium trioxide (BkO3). The oxidation states seen so far are +3 and +4 in accordance to its position below terbium in the periodic table.

In 1962 visible amounts of berkelium chloride were isolated, weighing 3 billionth of a gram. This was the first time that visible amounts of a pure berkelium compound had been produced.

Like other actinides, berkelium accumulates in skeletal tissue and is therefore highly toxic to humans. The element has not found any uses yet outside of basic research and plays no known biological role. Nevertheless its discovery was an important step towards the synthesis of the superheavy elements and has served to test theories of nuclear physics as well as showing that the predictions of the periodic table are fulfilled well beyond the elements for which it was originally devised.

Meera Senthilingam

Sp playing a pivotal role in fundamental chemistry and physics, while also testing the chemical knowledge of postal services worldwide. That was scientist and author Eric Scerri from UCLA with the discovery of Berkelium. Now next week, an element that requires a magic touch - as long as you don't get too close.

Peter Wothers

The next exciting thing about caesium, is that my love is not unrequited, it responds to my touch. Strictly speaking, it's the warmth from the hand that melts it, given that its melting point is only 28.4 °C. So just holding its container converts the crystalline solid into liquid gold. Liquid metals are always fascinating - everyone loves mercury; just imagine playing with liquid gold!

But here's the snag that adds to my fascination with this metal - it has a rather fiery temper. In fact, you can't actually touch the metal itself since it spontaneously bursts into flames in the presence of air and reacts explosively with water. Awkward indeed. My caesium is sealed inside a glass tube under an atmosphere of the chemically inert gas argon. So to play with it, you have to hold the glass tube, knowing that if you accidentally crushed it, or dropped it, all hell would break loose.

Meera Senthilingam

And as well as a possible adrenalin rush, join Cambridge University's Peter Wothers for more exciting facts about the liquid gold element that is caesium in next week's Chemistry in its element. Until then thank you for listening, I'm Meera Senthilingam.


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.