Glossary


Allotropes
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.

 

Glossary


Group
A vertical column in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
A horizontal row in the periodic table. The atomic number of each element increases by one, reading from left to right.


Block
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.


Sublimation
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.


Isotopes
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 3185°C, 5765°F, 3458 K 
Period Boiling point 5590°C, 10094°F, 5863 K 
Block Density (g cm−3) 20.8 
Atomic number 75  Relative atomic mass 186.207  
State at 20°C Solid  Key isotopes 187Re 
Electron configuration [Xe] 4f145d56s2  CAS number 7440-15-5 
ChemSpider ID 22388 ChemSpider is a free chemical structure database
 

Glossary


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.


Appearance

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 symbol is based on the coat of arms of Mainz, the capital of the German state of Rhineland-Palatinate.
Appearance
A metal with a very high melting point.  Tungsten is the only metallic element with a higher melting point.
Uses
Rhenium is used as an additive to tungsten- and molybdenum-based alloys to give useful properties. These alloys are used for oven filaments and x-ray machines. It is also used as an electrical contact material as it resists wear and withstands arc corrosion.

Rhenium catalysts are extremely resistant to poisoning (deactivation) and are used for the hydrogenation of fine chemicals. Some rhenium is used in nickel alloys to make single-crystal turbine blades.
Biological role
Rhenium has no known biological role.
Natural abundance
Rhenium is among the rarest metals on Earth. It does not occur uncombined in nature or as a compound in a mineable mineral species. It is, however, widely spread throughout the Earth’s crust to the extent of about 0.001 parts per million. Commercial production of rhenium is by extraction from the flue dusts of molybdenum smelters.
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History

The periodic table had two vacant slots below manganese and finding these missing elements, technetium and rhenium, proved difficult. Rhenium was the lower one and indeed it was the last stable, non-radioactive, naturally-occurring element to be discovered. In 1905, Masataka Ogawa found it in the mineral thorianite from Sri Lanka. He realised from lines in its atomic spectrum that it contained an unknown element. He wrongly thought it was the one directly below manganese and so his claim was discounted at the time. However, a re-examination of Ogawa’s original photographic spectra proved he had discovered rhenium.

The isolation of rhenium was finally achieved in May 1925 by Walter Noddack and Ida Tacke working in Berlin. They concentrated it from the ore gadolinite in which it was an impurity.
 
Glossary

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) 2.16 Covalent radius (Å) 1.41
Electron affinity (kJ mol−1) 14.47 Electronegativity
(Pauling scale)
1.9
Ionisation energies
(kJ mol−1)
 
1st
755.82
2nd
-
3rd
-
4th
-
5th
-
6th
-
7th
-
8th
-
 

Glossary


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.


Isotopes

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 7, 6, 4, 2, -1
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  185Re 184.953 37.4
  187Re 186.956 62.6 4.16 x 1010 β- 
 

Glossary

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.


Substitutability

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 6.2
Crustal abundance (ppm) 0.000188
Recycling rate (%) >30
Substitutability High
Production concentration (%) 51
Reserve distribution (%) 52
Top 3 producers
  • 1) Chile
  • 2) USA
  • 3) Poland
Top 3 reserve holders
  • 1) Chile
  • 2) USA
  • 3) Russia
Political stability of top producer 67.5
Political stability of top reserve holder 67.5
 

Glossary


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)
137 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)
- - - - - - - 1.37
x 10-10
2.22
x 10-8
1.41
x 10-6
4.45
x 10-5
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Podcasts

Listen to Rhenium Podcast
Transcript :

Chemistry in its element: rhenium


(Promo)

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 one of the rarest elements on earth that seems to enjoy changing the laws of nature. Unraveling the mysteries of rhenium, here's UCLA's Eric Scerri.

Eric Scerri

Rhenium is element 75 in the periodic table and in many ways a rather unusual element. It is one of the rarest elements on the Earth with an abundance of something like 1 part per million. It is also one of the densest elements, following only platinum, iridium and osmium and it is one of the highest melting point elements exceeded only by tungsten and carbon.

Rhenium sits two places below manganese in the periodic table and its existence was first predicted by Mendeleev when he first proposed his periodic table in 1869. In fact this group is unusual in that, when the periodic table was first published, it possessed only one known element, manganese, with at least two gaps below it. The first gap was eventually filled by element 43 technetium, the second gap was filled by rhenium. But rhenium was the first to be discovered.

It was first isolated in 1925 by Walter and Ida Noddack and Otto Berg in Germany. In the course of an extraction of epic proportions, they processed about 660 kg of the ore molybdenite in order to get just one gram of rhenium. These days rhenium is extracted more efficiently as the bi-product of the processes for the purification of molybdenum and copper, since rhenium often occurs as an impurity in the ores of these elements.

The discoverers called their element, rhenium, after the Latin name Rhenus for the river Rhine close to the place where they were working. In fact the Noddacks and Berg believed that they had also isolated the other element missing from group 7, or element 43, that eventually became known as technetium, but it was not to be.

As recently as the early years of the 21st century some researchers from Belgium and the US re-analyzed the X-ray evidence from the Noddacks and argued that they had in fact isolated element 43. But these claims have been hotly debated by many radiochemists and physicists and now have been finally laid to rest.

But by an odd twist of fate, a Japanese chemist, Masataka Ogawa believed that he had isolated element 43 and called it nipponium back in 1908. His claim too was largely discredited but as recently as 2004 it has emerged that he had in fact isolated rhenium well before the Noddacks.

Until quite recently no mineral containing rhenium combined with just a non-metal had ever been found. Not until 1992 that is, when a team of Russian scientists discovered rhenium disulphide at the mouth of a volcano on an islands off the east coast of Russia between the Kamchatka peninsula and the Japanese islands.

The chemistry of rhenium is also rather interesting. For example, it shows the largest range of oxidation states of absolutely any known element, namely -1, 0, +1, +2 and so on all the way to +7, the last of which is actually its most common oxidation state.

Now here is another oddity. Until the early 1960s it was believed that three bonds between any two atoms was as high as nature could go, as in the case of the nitrogen-nitrogen triple bond for example. But in 1964 Albert Cotton and co-workers in the USA discovered the existence of a metal-metal quadruple bond. Yes you guessed it, it was rhenium, or rather a rhenium compound namely the rhenium ion, [Re2Cl8]2+ [correction: this should be the two minus ion, not the two plus ion].

More recently an especially simple compound of rhenium, rhenium dibromide, has attracted a great deal of scientific attention because it is one of the hardest of all known substances. And unlike other super-hard materials, like diamond, it does not have to be manufactured under high pressure conditions.

But what else is rhenium good for? What are some other applications? Well there are many of them. A good deal of the rhenium extracted is made into super-alloys to be used for parts in jet engines. Not surprisingly for a transition metal, rhenium is also a good catalyst. In fact a combination of rhenium and platinum make up the catalyst of choice in the very important process of making lead-free and high-octane petrol. Rhenium catalysts are especially resistant to chemical attack from nitrogen, phosphorus, and sulfur, which also makes them useful in hydrogenation reactions in various industrial processes.

And just to go back to the Noddacks, and in particular Ida Noddack, it was she who first proposed in 1934 that nuclear fission might be possible as the result of the break up of a nucleus into fragments but her speculation was ignored and it had to wait until 1939 when Hahn, Strassmann and Meitner really discovered fission. Why was Noddack ignored? The most popular view seems to be that it was because her reputation had been damaged by her falsely announcing the discovery of element 43 in addition to the correct discovery of rhenium.

Meera Senthilingam

So its one of the hardest of all known substances, has a variety of oxidation states, and has the ability to make quadruple bonds, certainly a rule breaker. That was Eric Scerri from the University of California Los Angeles, revealing the secret powers of rhenium. Next week, a colourful luminous element.

Louise Natrajan

Terbium in the +3 state radiates an aesthetically pleasing luminous green colour when the correct wavelength of energy is used to excite the atoms. This is because terbium 3+ ions are strongly luminescent, so strong in fact, that its luminescence can often be seen by the naked eye The human eye is particularly sensitive to the colour green and even small amounts in the right compound are easily detectable by eye. This bright colour renders terbium compounds particularly useful as colour phosphors in lighting applications, e.g. in fluorescent lamps, where it is a yellow colour, and as with europium(III) which is red, provides one of the primary colours in TV screens; who knew that Turbium could be in your TV set!

Meera Senthilingam

And Manchester University's Louise Natrajan will be filling us in on the colourful story of terbium in next week's Chemistry in its element. Until then I'm Meera Senthilingam and thank you for listening.

(Promo)

Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements.

(End promo)
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References

Visual Elements images and videos
© Murray Robertson 2011.

 

Data

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 3.0), 2010, National Institute of Standards and Technology, Gaithersburg, MD, accessed December 2014.
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

© John Emsley 2012.

 

Podcasts

Produced by The Naked Scientists.

 

Periodic Table of Videos

Created by video journalist Brady Haran working with chemists at The University of Nottingham.
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