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 Melting point 1495°C, 2723°F, 1768 K 
Period Boiling point 2927°C, 5301°F, 3200 K 
Block Density (g cm−3) 8.86 
Atomic number 27  Relative atomic mass 58.933  
State at 20°C Solid  Key isotopes 59Co 
Electron configuration [Ar] 3d74s2  CAS number 7440-48-4 
ChemSpider ID 94547 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 goblin or ‘kobold’ (often accused of leading German miners astray in their search for tin). In the background is some early Chinese porcelain, which used the element cobalt to give it its blue glaze.
A lustrous, silvery-blue metal. It is magnetic.
Cobalt, like iron, can be magnetised and so is used to make magnets. It is alloyed with aluminium and nickel to make particularly powerful magnets.

Other alloys of cobalt are used in jet turbines and gas turbine generators, where high-temperature strength is important.

Cobalt metal is sometimes used in electroplating because of its attractive appearance, hardness and resistance to corrosion.

Cobalt salts have been used for centuries to produce brilliant blue colours in paint, porcelain, glass, pottery and enamels.

Radioactive cobalt-60 is used to treat cancer and, in some countries, to irradiate food to preserve it.
Biological role
Cobalt is an essential trace element, and forms part of the active site of vitamin B12. The amount we need is very small, and the body contains only about 1 milligram. Cobalt salts can be given to certain animals in small doses to correct mineral deficiencies. In large doses cobalt is carcinogenic.

Cobalt-60 is a radioactive isotope. It is an important source of gamma-rays. It is widely used in cancer treatment, as a tracer and for radiotherapy.
Natural abundance
Cobalt is found in the minerals cobaltite, skutterudite and erythrite. Important ore deposits are found in DR Congo, Canada, Australia, Zambia and Brazil. Most cobalt is formed as a by-product of nickel refining.

A huge reserve of several transition metals (including cobalt) can be found in strange nodules on the floors of the deepest oceans. The nodules are manganese minerals that take millions of years to form, and together they contain many tonnes of cobalt.
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The tomb of Pharaoh Tutankhamen, who ruled from 1361-1352 BC, contained a small glass object coloured deep blue with cobalt. Cobalt blue was known even earlier in China and was used for pottery glazes.

In 1730, chemist Georg Brandt of Stockholm became interested in a dark blue ore from some local copper workings and he eventually proved that it contained a hitherto unrecognised metal and he gave it the name by which its ore was cursed by miners in Germany, where it was sometimes mistaken for a silver ore. He published his results in 1739. For many years his claim to have uncovered a new metal was disputed by other chemists who said his new element was really a compound of iron and arsenic, but eventually it was recognised as an element in its own right.

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) 2.00 Covalent radius (Å) 1.18
Electron affinity (kJ mol−1) 63.873 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, 2, 0, -1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  59Co 58.933 100


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.

Supply risk

Relative supply risk 7.6
Crustal abundance (ppm) 26.6
Recycling rate (%) >30
Substitutability Medium
Production concentration (%) 67
Reserve distribution (%) 45
Top 3 producers
  • 1) DRC
  • 2) China
  • 3) Zambia
Top 3 reserve holders
  • 1) DRC
  • 2) Australia
  • 3) Cuba
Political stability of top producer 2.8
Political stability of top reserve holder 2.8


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)
421 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)
- - - 2.09
x 10-10
x 10-6
0.000419 0.0379 1.15 16 - -
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Listen to Cobalt Podcast
Transcript :

Chemistry in its element: cobalt


You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

(End promo)

Chris Smith

Hello - beauty, blue glass, B12 and the best magnets that money can buy. So why is this week's element named after a goblin?

Sarah Staniland

I always find the question 'what's your favourite element' a difficult one. There are several front runners for vastly varying reasons; however, always a top contender has to be cobalt because it excels in several important character traits: Cobalt has amazing beauty and strength, as well as great cooperation. All together a highly useful metal.

Before I even thought about the chemistry of colour I developed a love for blue glass, something I still collect to this day. Only after studying the transition metal chemistry did I realise that this beautiful blue colour comes from cobalt. Cobalt chloride in fact.

However, as far as colours go, cobalt has a few more strings to its bow than just this wonderful blue. Cobalt can also colour glass green, while the hydrated form of cobalt chloride is a beautiful deep rose colour. As you can imagine this colour change due to the presence of water is highly useful, warranting cobalt chloride an ideal moisture indicator.

The array of beautiful colours that cobalt produces were never more prevalent to me than when I went to the cobalt mining region called the Copperbelt in Zambia. In this area the huge multicoloured cobalt minerals deposits tower high, with the shores of dams and streams coloured deep rose with silvery blue veins running through.

Cobalt it is not found pure in Nature but found in sulphur minerals and usually associated with other transition metals. As you can probably guess from the name of the region in Zambia - the Copperbelt, cobalt is mined as a secondary product to copper that is dominant in the ore of this region. Because of this cobalt is normally recovered from the waste of the primary metal extraction.

However these mining hotspots are not the only places on the Earth where high concentrations of cobalt can be found. A huge reserve of several transition metals (including cobalt) can be found in strange nodules on the floors of the deepest oceans. The nodules are manganese minerals that take millions of years to form, and there are many tonnes of cobalt present in this form.

So you can see that cobalt is never found alone but always palled up with other transition metals in their ores, mainly copper and nickel. In fact cobalt metal was not isolated and purified until as late as 1735 by the Swedish scientist G. Brandt.

Cobalt can also sometimes be found in mixed arsenic ores, and it is cobalt's association with arsenic that gives it its name. The word cobalt comes from the German "Kobolds" which means goblin or trouble maker. It was so called in this early mining region because it was very difficult to smelt without oxidising and smelting would release the associated arsenic vapours which would lead to pretty troublesome or even deadly processing conditions for the worker. The Kobolds were blamed and the name stuck.

With the exception of the mining region, cobalt is not very abundant, with only trace amounts in the Earths crust (about 2500 times less than iron). However, it is a metal that is essential for life in the trace amounts. Cobalt is the metal at the centre of vitamin B12 which helps regulate cell development and therefore DNA and energy production in the body.

Cobalt has been known and used by people for its beautiful colouring and pigment properties as far back as 2500BC. Egyptian cobalt blue paints and Prussian cobalt oxide necklaces have been dated back to this time while cobalt glass has been found in a Greek vase dated at 100 BC. Cobalt was also used to colour glass in the Chinese Tang dynasty from 618 AD. In fact all the way up until the beginning of the 20th century people have only really exploited cobalt for its beautiful colour.

However cobalt is not just a pretty face. Cobalt is a lustrous very hard silvery metal belonging to a group called the "transition metals". It is one of only 3 ferromagnetic transition elements along with iron and nickel. As a metal it is very mechanically hard and tough, and it has a very high melting point (hence the smelting problems) and also remains magnetic to the highest temperature of all the magnetic elements.

When cobalt is combined with other metals its strength allow a range of super alloys to be created. In particular, cobalt's very high melting point and mechanical strength at high temperatures has seen its extensive use in what is termed 'superalloys'. These are alloys that retain mechanical strength at high temperatures. Because of its impressive properties cobalt is an important component in wear resistant and corrosive resistant alloys. And cobalt alloys and coatings are seen everywhere from drills to saws, from aircraft turbines to prosthetic bone replacements.

The fact that cobalt is magnetic has also been exploited with the Japanese invention of cobalt magnetic steel where adding cobalt to steel vastly increases the magnetic hardness. Just a few years after that in the 1930s saw the pivotal invention of Alnico magnets, which as the name suggests, are composed of aluminium, nickel and cobalt.

The fact that cobalt retains its magnetism up to high temperatures is also a very favourable trait when the addition of cobalt to a magnetic material can improve its properties at high temperatures. More recently the creation of rare-earth magnets have given us much stronger, harder, permanent magnets than Alnico magnets. One such magnetic material, samarium cobalt retains its magnetism up to 800°C. Because it is magnetically and mechanically hard up to very high temperatures, it has found uses in high-speed motors and turbo machinery. More recently cobalt has a major use in newer batteries, magnetic particles for recording and storage information in magnetic tapes and hard drives.

So cobalt; giving joy in an array of beautiful colours, but also ultra strong, hard and magnetic. Cobalt is never alone, it is found associated with different metals in their ore and has its best mechanical properties when palled up with others.

Chris Smith

Emphasising the importance, of course, of teamwork. That was Sarah Staniland with the story of Cobalt - she's based at the University of Leeds. Next week it's the turn of the stuff that amongst other things makes Parker pen nibs write so nicely, but if you haven't heard of it before, then you're probably in good company.

Jonathan Steed

Stop the proverbial "man in the street" and ask him what ruthenium is and the chances are he won't be able to tell you. Compared to the "sexier elements" that are household names like carbon and oxygen, ruthenium is, frankly, a bit obscure. In fact even if your man in the street was wearing a lab coat and walking on a street very close to a university chemistry department he might still be a bit ignorant about this mysterious metal. It wasn't always that way, though.

Chris Smith

And you can hear how ruthenium rose to prominence with Jonathan Steed on next week's Chemistry in its Element. I'm Chris Smith, thank you for listening and goodbye.


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.