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.
| Discovery date | 1781 |
| Discovered by | Peter Jacob Hjelm |
| Origin of the name | The name is derived from the Greek 'molybdos' meaning lead. |
| Allotropes |
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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.
| Group | 6 | Melting point | 2622°C, 4752°F, 2895 K |
| Period | 5 | Boiling point | 4639°C, 8382°F, 4912 K |
| Block | d | Density (g cm−3) | 10.2 |
| Atomic number | 42 | Relative atomic mass | 95.95 |
| State at 20°C | Solid | Key isotopes | 95Mo, 96Mo, 98Mo |
| Electron configuration | [Kr] 4d55s1 | CAS number | 7439-98-7 |
| ChemSpider ID | 22374 | 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.
History
History
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.
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 | |
| Common oxidation states | 6, 5, 4, 3, 2, 0 | ||||
| Isotopes | Isotope | Atomic mass | Natural abundance (%) | Half life | Mode of decay |
| 92Mo | 91.907 | 14.53 | > 3 x 1017 y | β+-EC | |
| 94Mo | 93.905 | 9.15 | - | - | |
| 95Mo | 94.906 | 15.8 | - | - | |
| 96Mo | 95.905 | 16.67 | - | - | |
| 97Mo | 96.906 | 9.60 | - | - | |
| 98Mo | 97.905 | 24.39 | - | - | |
| 100Mo | 99.907 | 9.82 | 6 x 1020 y | β-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.
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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.
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Specific heat capacity (J kg−1 K−1) |
251 | Young's modulus (GPa) | Unknown | |||||||||||
| Shear modulus (GPa) | Unknown | Bulk modulus (GPa) | 231 | |||||||||||
| Vapour pressure | ||||||||||||||
| Temperature (K) |
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| Pressure (Pa) |
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Podcasts
Podcasts
| Listen to Molybdenum Podcast |
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Transcript :
Chemistry in its element: molybdenumPromo) 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, we clarify the importance of the often misunderstood molybdenum. Here's Quentin Cooper: Quentin Cooper The answer to the ultimate question - of life, the Universe and Everything - is, as every Douglas Adams fan knows, 42. And 42, as every Mendeleev fan knows, is the atomic number of molybdenum. And for many that - plus the indisputable fact that molybdenum is a funny word - is often about as far as their knowledge goes of this silvery metal - not that they'd have known it was a silvery metal - which is wedged between its better known brethren chromium and tungsten in group six of the periodic table. That odd-sounding name comes in a convoluted way from the Greek for lead, as ores of the two were often mixed up by early mineralogists - it was also frequently mistaken for graphite - and it wasn't until 1778 that molybdenum was recognised as a distinct entity deserving its own place in the periodic table, and a few years later still that it was finally isolated. The key breakthrough came from the Swedish chemist Carl Wilhlelm Scheele, better known as 'Hard luck Scheele' because he made a whole series of chemical discoveries, including oxygen, only for others to go and get the credit. So its mistaken-identity history, its miscredited discoverer, its misleading and often mis-spelled name, all add to the aura of comedy and confusion around molybdenum.....and yet it's an element that's right at the root of life - not just human life, but pretty much all life on the planet: yes you'll find tiny amounts of it in everything from the filaments of electric heaters to missiles to protective coatings in boilers, and its high performance at high temperatures mean it has a range of commercial applications: it's useful in toughening up steel and giving it more corrosion resistance, as a catalyst in processes such as refining petroleum, and above all it's turned to when you need things to get hot but stay slippy - where WD40 and other petroleum derived oils are at risk of igniting, molybdenum sulfides are the basis of a range of lubricants which can cope with the heat and keep things moving smoothly. But for all the ways we've discovered to use it, of far greater significance - although involving far smaller quantities of molybdenum - is the way we've evolved to make use of it within us. It's found in dozens of enzymes... including all important nitrogenase, which allows the most abundant element in the atmosphere, nitrogen, to be taken up and turned into compounds that enable bacteria, plants, us and everything between to synthesise and utilise proteins. Without proteins there wouldn't be much at all in the way of life....and without molybdenum there wouldn't be much at all in the way of proteins. And it turns up in other key human enzymes too such as xanthine oxidase in the liver, which is vital to our waste processing. But just in case anyone's thinking of rushing off to buy one of the many commercially available trace mineral supplements with molybdenum it's worth adding that although like much of life on Earth we definitely need it.... we don't need that much of it: about a third of a gram is all you'll get through in an entire lifetime. That's next to nothing...but without it we'd be next to nothingness. So, time to stop laughing at the funny name... molybdenum really is one of life's few true essentials. Meera Senthilingham So time to give some much-owed respect, it seems, to the element molybdenum. That was science broadcaster Quentin Cooper with the widely applied chemistry of molybdenum. Now, next week, blink and you may miss it. Brian Clegg If elements were insects, darmstadtium would be the mayfly of the chemical world. It exists for the most fleeting time before it transforms to something else. Darmstadium is never going to have a practical use - but its sheer brevity of existence gives it a wistful fascination. Meera Senthilingham And to find out what does happen in darmstadtium's brief existence on earth, in next week's Chemistry in its element. Until then, I'm Meera Senthilingham 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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Video
Video
Resources
Resources
Terms & Conditions
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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 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.
Podcasts
Produced by The Naked Scientists.
Periodic Table of Videos
Created by video journalist Brady Haran working with chemists at The University of Nottingham.
