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 Lanthanides  Melting point 1472°C, 2682°F, 1745 K 
Period Boiling point 2700°C, 4892°F, 2973 K 
Block Density (g cm−3) 8.80 
Atomic number 67  Relative atomic mass 164.930  
State at 20°C Solid  Key isotopes 165Ho 
Electron configuration [Xe] 4f116s2  CAS number 7440-60-0 
ChemSpider ID 22424 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 based upon the civic coat of arms of Stockholm, the city that gives the element its name.
A bright, silvery metal.
Holmium can absorb neutrons, so it is used in nuclear reactors to keep a chain reaction under control. Its alloys are used in some magnets.
Biological role
Holmium has no known biological role, and is non-toxic.
Natural abundance
Holmium is found as a minor component of the minerals monazite and bastnaesite. It is extracted from those ores that are processed to extract yttrium. It is obtained by ion exchange and solvent extraction.
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Holmium was discovered at Geneva in 1878 by Marc Delafontaine and Louis Soret, and independently by Per Teodor Cleve at Uppsala, Sweden. Both teams were investigating yttrium, which was contaminated with traces of other rare earths (aka lanthanoids) and had already yielded erbium which was later to yield ytterbium. Cleve looked more closely at what remained after the ytterbium had been removed, and realised it must contain yet other elements because he found that its atomic weight depended on its source. He separated holmium from erbium in 1878. Delafontaine and Soret also extracted it from the same source, having seen unexplained lines in the atomic spectrum. We cannot be certain that either group had produced a pure sample of the new element because yet another rare-earth, dysprosium, was to be extracted from holmium.

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) 2.30 Covalent radius (Å) 1.79
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
  165Ho 164.930 100


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 9.5
Crustal abundance (ppm) 0.3
Recycling rate (%) <10
Substitutability High
Production concentration (%) 97
Reserve distribution (%) 50
Top 3 producers
  • 1) China
  • 2) Russia
  • 3) Malaysia
Top 3 reserve holders
  • 1) China
  • 2) CIS Countries (inc. Russia)
  • 3) USA
Political stability of top producer 24.1
Political stability of top reserve holder 24.1


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)
165 Young's modulus (GPa) 64.8
Shear modulus (GPa) 26.3 Bulk modulus (GPa) 40.2
Vapour pressure  
Temperature (K)
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Pressure (Pa)
- - 3.20
x 10-9
x 10-5
0.00837 0.546 12.3 - - - -
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Listen to Holmium Podcast
Transcript :

Chemistry in its element: holmium


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

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Meera Senthilingam

This week, mythical monopoles that could lead us into another dimension.

Hayley Birch

In 1949, Milton Smith published a short work of fiction that he entitled The Mystery of Element 117. The real element 117 is yet to be discovered - it's a blank space in the Periodic Table just below the halogens. Smith's 117, however, was a strange material that could be used to open a window to another dimension. He called it a magnetic monopole substance - one that instead of having poles, plural, like an ordinary magnet, had a pole. Singular.

Now, whilst no reputable scientist would argue that a magnetic monopole could open an inter-dimensional portal, its existence isn't outside the realms of possibility and if recent reports are anything to go by, it could depend on an otherwise mundane metallic element that you can find skulking around near the bottom of the Periodic Table - holmium.

Despite having little else to shout about - bar a silvery sheen and a bit part in controlling nuclear reactions - holmium has some pretty fascinating magnetic properties. In fact, it has the strongest magnetic force of any element, albeit it as a paramagnet, which means it only becomes magnetic when it's sitting in an externally applied magnetic field.

Perhaps most interesting are recent experiments that involved using holmium to try to find the mythical magnetic monopole. First though, let's create some context. As we know, the monopole has acquired the kind of fringe scientific status that makes it worthy of mention in science fiction circles - besides its appearance in Element 117, the author Larry Niven references monopoles in his 1973 novel Protector, where he imagines one of his characters mining shovelfuls of north poles from the rings of Saturn.

But monopoles have also been the subject of much real scientific debate. The basis for their existence relies on work by the Nobel Prize-winning physicist Paul Dirac. According to theories, singular magnetic charges - monopoles - must exist in order to adhere to the grand unified theory of physics; to mirror the singular electric charges of elementary particles.

In 1982, a Stanford University physicist called Blas Cabrera thought he'd found one when, on Valentine's night, his "superconducting quantum interference detector" recorded a massive jump in the current fluctuations it was designed to monitor, indicating the existence of what he claimed to be a monopole. Cabrera and his troop of monopole hunters were given extra funding to build a bigger and better detector, but eventually abandoned their hunt in favour of a search for something similarly mysterious and just as elusive: dark matter.

Monopoles are even talked about in the same breath as the ever elusive Higg's boson, with whisperings that CERN scientists could create them, along with black holes, in their experiments at the LHC. So last year, when French scientists claimed to have found magnetic components in holmium titanate crystals that behaved for all intents and purposes like monopoles, they sparked a minor media storm. The crystals contained tiny north and south pole points that were separated by less than a nanometre.

Understandably, however, some scientists took issue with the use of the term "monopole" in this instance and argued that because that because one of these north points couldn't be created without the corresponding south point, the team hadn't found true monopoles.

So that's about as glamorous and interesting as holmium gets - a minor role in a science fiction story and in a search that may, for all we know, end in nothing but disappointment. And as the 56th most abundant element, it's twenty times more common than silver and hardly deserving of its "rare earth metal" label. In fact, in oxide form, it's used to colour cubic zirconia, the synthetic material that's sold as a cheap substitute for real gemstones. It is also found in very, very small amounts in the body and affects metabolism in certain bacteria, but it doesn't seem to be essential and no one really knows what, exactly, it does.

But perhaps I've been a bit harsh on poor old holmium, which, to be fair, doesn't get a whole lot of press. Because it does perform another useful task that's deserving of a mention. Some of the most cutting edge lasers used to treat certain cancers are solid-state lasers that require holmium to dope yttrium aluminium crystals. The lasers can be used to vaporise tumours with only minor tissue damage; a patient with early stage bladder cancer can be in and out of hospital in an afternoon without a general anaesthetic.

So there you have it: mythical monopoles and vaporising lasers. Not bad for an element you barely even knew existed.

Meera Senthilingam

So the search for the monopole continues, but vaporising tumours with minimal tissue damage is definitely a noteworthy application of holmium. That was science writer Hayley Birch with the mythical chemistry of holmium. Now, staying on treatments for cancer next week's element also has a radiating way to kill cancer cells.

Richard Corfield

225Ac can be used as the active agent Targeted Alpha Therapy, also known as TAT,a technique for inhibiting the growth of secondary cancers by direct irradiation with nuclear material. And so an element discovered in the same mineral - pitchblende - which kick-started the whole science of nuclear chemistry, today stands at the crossroads of one of the most challenging of all medical disciplines - finding a cure for cancer.

Meera Senthilingam

And Oxford's Richard Corfield will be revealing more uses for actinium as well as the origin of the actinides 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

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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.



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