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 | 1829 |
| Discovered by | Jöns Jacob Berzelius |
| Origin of the name | Thorium is named after Thor, the Scandinavian god of war. |
| 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 | Actinides | Melting point | 1750°C, 3182°F, 2023 K |
| Period | 7 | Boiling point | 4785°C, 8645°F, 5058 K |
| Block | f | Density (g cm−3) | 11.7 |
| Atomic number | 90 | Relative atomic mass | 232.038 |
| State at 20°C | Solid | Key isotopes | 230Th, 232Th |
| Electron configuration | [Rn] 6d27s2 | CAS number | 7440-29-1 |
| ChemSpider ID | 22399 | 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 | |
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) |
118 | Young's modulus (GPa) | Unknown | |||||||||||
| Shear modulus (GPa) | Unknown | Bulk modulus (GPa) | Unknown | |||||||||||
| Vapour pressure | ||||||||||||||
| Temperature (K) |
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| Pressure (Pa) |
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Podcasts
Podcasts
| Listen to Thorium Podcast |
|
Transcript :
Chemistry in its element - thorium(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, the no risk, no fear discovery of elements. Here's Lars Öhrström: Lars Öhrström Frequently after more spectacular chemistry demonstrations, the scientist on stage will warn the audience 'not to try this at home'. One person who certainly did not listen to such warnings was Swedish chemist Jöns Jacob Berzelius. Instead, he and his co-workers performed many groundbreaking experiments in the kitchen of his flat in the corner of Nybrogatan and Riddargatan in Stockholm. In 1815, for example, Berzelius isolated a new element from a mineral sent to him from the Swedish mining town of Falun and named it thorium after the Scandinavian god of thunder, Thor. Only to realise a few years later that he was wrong and what he though was a new element was in fact yttrium phosphate. However, in 1828, by then long since world famous and credited with discovering three other elements, he received a strange mineral sample from the reverend Hans Esmark in Norway. In his new laboratory at the Swedish Royal Academy of Sciences, Berzelius isolated yet another element, and because he liked the name or because of a superficial resemblance of the minerals, this element is what we now call thorium, with the symbol Th. While Berzelius did figure out many of the chemical properties of this new element, one crucial characteristic escaped him, its radioactivity. This should not surprise us though, as the phenomenon of radioactivity was not discovered until long after his death by Henri Becquerel in 1896. Today, its radioactivity seems logical as when we look at the periodic table, we find thorium, element 90, just after actinium in the last row of the periodic table known as the actinides, comprising of famous radioactive elements such as uranium and plutonium. In the years after its discovery, thorium rested mostly undisturbed on the laboratory shelves until called to duty to light up the streets and homes of the world's metropoles. This was because of another of its remarkable properties: its oxide ThO2 has the highest melting point of all known oxides. Thus in the fierce heat in the flame of burning gas it would not melt, but glow intensively with a bright white light, making thorium oxide incandescent gas mantles the obvious choice for gaslight devices all over the world. The importance of gaslight is now forgotten, but arguably this was a greater advance than the invention of the electric light, because for first time in history abundant light was available after sunset. Initially, other metal oxides were used, but besides problems with the melting points, the colour of the light they gave off was not quite right, and so in 1891 Austrian chemist Auer von Welsbach came up with the thorium solution after a first failed attempt with a magnesium, lanthanum and yttrium product in 1885. Now, you may think that this was in fact a poisoned gift and that the upper classes of the late 19th century, after years of radioactive exposure from decaying thorium atoms, suffered from radiation related illnesses. But thankfully this wasn't so. Thorium decays by emitting alpha particles, and these alpha particles, or helium two plus ions, as they should really be called, do not travel very far and are easily stopped by the glass cover of a gas lantern and even the human skin. In fact, thorium oxide mantles are still in use today, and you may even have come into contact with them yourself in camping lanterns. They are completely harmless unless you eat them, or inhale the powder from pulverized mantles. However, as the manufacture requires large amounts of thorium oxide, it is preferred to avoid it, and normally, most gas mantles sold in outdoors equipment shops today are advertised as 'thorium free'. But the next time you stock up for your camping expedition, by all means, bring your Geiger counter! So, short from eating it, there are no particular worries in handling such tiny amounts of thorium oxide. However, eating it was just the point when using the x-ray contrast agent thorotrast, a state-of-the-art diagnostic aid in the 1930s and 1940s, depending on thorium's excellent ability to absorb x-rays. Undoubtedly, the superior x-ray photographs generated this way saved many lives, so the risk of developing cancer some 20 years later was probably worth taking in serious cases. Thankfully, though, less dangerous contrast agents were soon developed. Thorium thus spent its first sixty years in obscurity, then had fifty years in the limelight. Thorium may be three times more abundant on Earth than uranium, it is difficult to estimate, and can also be used in nuclear reactors. In addition, thorium and uranium deposits do not necessarily occur at the same places, thus countries with large potential uranium resources may well have very little thorium and vice-versa. The proponents of this so called thorium fuel cycle also claim it has important technical advantages, but it seems hopes for "burning" weapon grade plutonium or producing waste with reduced risks of nuclear arms proliferation are largely unfounded. On the contrary, the high melting point of the oxide is a drawback in this application as it makes the preparation of the fuel more difficult. So, although a number of nuclear reactors worldwide have been run on thorium-based fuels the last decades, and some have even been connected to the electrical grid, it may yet be a long time until our houses and streets are again lit up with thorium based technology. Meera Senthilingam So time will tell if Thorium makes its comeback (with minimal exposure risks, that is). That was Lars Öhrström from the Chalmers tekniska högskola in Sweden, with the radioactive chemistry of Thorium. Now next week, an element that lived up to its predictions David Lindsay In 1879, Lars Nilson isolated the oxide of a new metal from the minerals gadolinite and euxenite. Nilson was a student of the legendary Jacob Berzelius, himself discoverer of many elements. Nilson named this oxide scandia, after Scandinavia. The discovery of this element was especially notable, as, seven years previously, Mendeleev had used his periodic table to predict the existence of ten as yet unknown elements, and for four of these, he predicted in great detail the properties they should have. One of these four, Mendeleev predicted, should have properties very similar to boron, and he named this new element "ekaboron", meaning "like boron". The metal of this new oxide, scandia, was indeed found to have similar properties to this "ekaboron", thus demonstrating the power of Mendeleev's construct. Meera Senthilingam And join Reading University's David Lindsay to find out what these properties of scandium were that resembled boron so closely, as well as its applications, 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) |
Video
Video
Resources
Resources
Terms & Conditions
Images © Murray Robertson 1999-2011
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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.
