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 2333°C, 4231°F, 2606 K 
Period Boiling point 4147°C, 7497°F, 4420 K 
Block Density (g cm−3) 12.1 
Atomic number 44  Relative atomic mass 101.07  
State at 20°C Solid  Key isotopes 101Ru, 102Ru, 104Ru 
Electron configuration [Kr] 4d75s1  CAS number 7440-18-8 
ChemSpider ID 22390 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 element’s name is derived from the Latin name for Russia. The stylised Cyrillic text is based on a Soviet Russian flag from around 1921.
A shiny, silvery metal.
Many new uses are emerging for ruthenium. Most is used in the electronics industry for chip resistors and electrical contacts. Ruthenium oxide is used in the chemical industry to coat the anodes of electrochemical cells for chlorine production. Ruthenium is also used in catalysts for ammonia and acetic acid production. Ruthenium compounds can be used in solar cells, which turn light energy into electrical energy.

Ruthenium is one of the most effective hardeners for platinum and palladium, and is alloyed with these metals to make electrical contacts for severe wear resistance. It is used in some jewellery as an alloy with platinum.
Biological role
Ruthenium has no known biological role. Ruthenium(IV) oxide is highly toxic.
Natural abundance
Ruthenium is one of the rarest metals on Earth. It is found uncombined in nature; however, it is more commonly found associated with other platinum metals in the minerals pentlandite and pyroxinite. It is obtained commercially from the wastes of nickel refining.
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The Polish chemist Jedrzej Sniadecki was investigating platinum ores from South America and, in May 1808, when he discovered a new metal which he called it vestium. However, when French chemists tried to repeat his work they were unable to find it in the platinum ore they had. When Sniadecki learned of this he believed he had been mistaken and withdrew his claim.

Then, in 1825, Gottfried Osann of the University of Dorpat (now Tartu) on the Baltic, investigated some platinum from the Ural mountains, and reported finding three new elements which he named pluranium, polinium, and ruthenium.

While the first two of these were never to be verified, the third was genuine and in 1840 Karl Karlovich Klaus at the University of Kazan extracted, purified, and confirmed it was a new metal. He kept Osann’s name of ruthenium.

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) 2.13 Covalent radius (Å) 1.36
Electron affinity (kJ mol−1) 101.31 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 8, 6, 4, 3, 2, 0, -2
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  96Ru 95.908 5.54 > 3.1 x 1016 β+β+ 
  98Ru 97.905 1.87
  99Ru 98.906 12.76
  100Ru 99.904 12.6
  101Ru 100.906 17.06
  102Ru 101.904 31.55
  104Ru 103.905 18.62


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) 0.000037
Recycling rate (%) >30
Substitutability High
Production concentration (%) 60
Reserve distribution (%) 95
Top 3 producers
  • 1) South Africa
  • 2) Russia
  • 3) Zimbabwe
Top 3 reserve holders
  • 1) South Africa
  • 2) Russia
  • 3) USA
Political stability of top producer 44.3
Political stability of top reserve holder 44.3


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)
238 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)
- - - - - - 7.96
x 10-9
x 10-6
0.000133 0.00455 0.0858
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Listen to Ruthenium Podcast
Transcript :

Chemistry in its element: ruthenium


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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Chris Smith

Hello, welcome to this week's Chemistry in its element, I'm Chris Smith. In this episode we come face to face with the chemical dubbed the connoisseur's element. It's won a nobel prize as a catalyst, it's the muscle behind wear resistant electrical contacts and it might even help you to write nicely, unless you're a doctor, in which case you're probably beyond redemption. Here's Jonathan Steed.

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. Twenty or thirty years ago whole generations of chemists did entire Ph.D.s on the chemistry of the metals of the so-called "platinum group" of which ruthenium is one. As one of that cohort of ruthenium chemists it is my duty to spread the word about the element once described by one of the fathers of modern inorganic chemistry, Sir Geoffrey Wilkinson as "an element for the connoisseur".

As I rustily recalled in response to the first question I was asked in my Ph.D. exam, the name "ruthenium" derives from Ruthenia, the Latin word for Rus', a historical area which includes present-day western Russia, Ukraine, Belarus, and parts of Slovakia and Poland. The name was first proposed by Gottfried Osann in 1828, who believed he had identified the metal, and the name was retained by Osann's countryman (and in 1844 ruthenium's official discoverer) Karl Klaus in honour of his birthplace in Tartu, Estonia; at the time a part of the Russian Empire.

Ruthenium's popularity in university chemistry departments in the latter half of the twentieth century was in no small part due to the fact that it is relatively cheap. The rarity of the platinum group metals (which are often found together) makes them all expensive but unlike platinum, rhodium and palladium which have use in automobile catalytic converters, for example, ruthenium was historically not so much in demand. Indeed for many years the metals company Johnson Matthey operated a loan scheme where they would give aspiring researchers 100 g or so of ruthenium trichloride to experiment with in the hope the chemists would find new uses for the material. The loans scheme operated for the pricier metals like rhodium as well, but only in little 5 g pots. A nice feature of the loans scheme was that chemists collected the metal-containing residues of their experiments and returned the resulting black, smelly sludge to the company for metals recovery.

So, from the 1960s onwards when the field of organometallic chemistry burst onto chemists' consciousness, a lot of people were doing a lot of research with the connoisseur's element. While it was a rhodium reaction that led the ever colourful Wilkinson to rush around his lab brandishing a foaming test tube and shouting "who wants a Ph.D.?", it certainly seemed true that Ph.Ds. were to be had for nothing more than boiling up any of the platinum group metals with as many organic materials as possible and analyzing the fascinating cornucopia of compounds that resulted.

It turns out that ruthenium does indeed deserve Wilkinson's elegant description. While the element itself is an unremarkable looking, rather hard, white metal it forms a vast range of interesting compounds that seem to have that perfect balance between reactivity and stability to make them generally useful but easy to handle. Like all of the platinum group metals, ruthenium complexes are good catalysts.

Wind the clock forward to 2005, when Yves Chauvin, Bob Grubbs and Dick Schrock were awarded the Nobel Prize in Chemistry "for the development of the metathesis method in organic synthesis"; this synthetic chemistry award was a real boost for the "pot boilers". And which of the platinum group metals is it that lies at the heart of Grubbs' elegant catalyst system for this fantastically useful, modern carbon-carbon bond forming reaction? It turns out that it is a cool carbene complex of the humble ruthenium that gets it just right.

It is this kind of niche application - just a little in the just the right place that I think Wilkinson was talking about. In fact, the harder you look the more you find just little bits of ruthenium stiffening the backbone of technology. Due to its hardness ruthenium is used in alloys with other platinum group metals to make wear-resistant electrical contacts, and there is a vast amount of interest in ruthenium-based thin film microelectronics because the metal can be easily patterned.

If you are fan of fountain pens then the chances are you have written with a ruthenium alloy. The famous Parker 51 fountain pen has been fitted with an Ru nib since 1944; a 14K gold nib tipped with 96.2% ruthenium and 3.8% iridium. Ruthenium compounds also have some nice optical and electronic properties. Like its lighter close relative, iron, ruthenium readily forms a number of oxides including some exotic oxygen bridged multi metallic compounds. One such material, ruthenium red, is a dye used to stain negatively charged biomolecules such as nucleic acids in microscopy. Ruthenium complexes also have significant potential as anti-cancer treatments.

One of my personal favourites in the zoo of exotic ruthenium complexes is the Creutz-Taube ion - two ruthenium atoms surrounded by ammonia molecules and joined by a molecule of pyrazene (imagine benzene but with a couple of nitrogen atoms). This was the first genuinely delocalized mixed valence complex. From the overall charge you know that one of the ruthenium ions has to have a +3 charge and one has to have +2 but there's just no way to work out which is which. It behaves for all the world as if the two metals have plus two and a half charges each even though charges only come in units of one! This compound gave rise to a whole field of "mixed valence" chemistry and is part of the tremendously exciting field of molecular electronics today.

So, when you think about chemistry and are watching yet another documentary on the vital importance of carbon, or the hydrogen economy, spare a thought for the rare, refined elements like ruthenium that are reserved only for the connoisseur.

Chris Smith

So that's why I can't read my own writing - perhaps Bic need to start incorporating some ruthenium in their roller balls. That was Durham University's Jonathan Steed. Next time to the stuff that's the bain of kettles and boilers everywhere - but there are some benefits too.

Karen Faulds

The calcium usually enters the water as it flows past either calcium carbonate, from limestone and chalk, or calcium sulfate, from other mineral deposits. Whilst some people do not like the taste, hard water is generally not harmful to your health. Although it does make your kettle furry! Interestingly, the taste of beer (something dear to my heart) seems related to the calcium concentration of the water used, and it is claimed that good beer should have a calcium concentration that is higher than that of hard tap water.

Chris Smith

And more importantly an alcohol concentration of at least 10%. No southern softies around here, thank you very much. Karen Faulds will be serving up the story of calcium on next week's Chemistry in its Element. I'm Chris Smith, thank you very much 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.