Periodic Table > Thorium
 

Terminology


Allotropes
Some elements exist in several different structural forms, these are called allotropes.


For more information on Murray Robertson’s image see Uses/Interesting Facts below.

 

Fact Box Terminology


Group
Elements appear in columns or ‘groups’ in the periodic table. Members of a group typically have similar properties and electron configurations in their outer shell.


Period
Elements are laid out into rows or ‘periods’ so that similar chemical behaviour is observed in columns.


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, principal, diffuse, and fundamental.


Atomic Number
The number of protons in the nucleus.


Atomic Radius/non -bonded (Å)
based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties, for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron Configuration
The arrangements of electrons above the last (closed shell) noble gas.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.


Melting Point (oC)
The temperature at which the solid-liquid phase change occurs.


Melting Point (K)
The temperature at which the solid-liquid phase change occurs.


Melting Point (oF)
The temperature at which the solid-liquid phase change occurs.


Boiling Point (oC)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (K)
The temperature at which the liquid-gas phase change occurs.


Boiling Point (oF)
The temperature at which the liquid-gas phase change occurs.


Sublimation
Elements that do not possess a liquid phase at atmospheric pressure (1 atm) are described as going through a sublimation process.


Density (kgm-3)
Density is the weight of a substance that would fill 1 m3 (at 298 K unless otherwise stated).


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.


Key Isotopes (% abundance)
An element must by definition have a fixed number of protons in its nucleus, and as such has a fixed atomic number, however variants of an element can exist with differing numbers of neutrons, and hence a different atomic masses (e.g. 12C has 6 protons and 6 neutrons and 13C has 6 protons and 7 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 (where several isotopes exist, a value is presented for the most prevalent isotope).

Fact Box

 
Group Actinides  Melting point 1750 oC, 3182 oF, 2023.15 K 
Period Boiling point 4785 oC, 8645 oF, 5058.15 K 
Block Density (kg m-3) 11725 
Atomic number 90  Relative atomic mass 232.038  
State at room temperature Solid  Key isotopes 230Th, 232Th 
Electron configuration [Rn] 6d27s2  CAS number 7440-29-1 
ChemSpider ID 22399 ChemSpider is a free chemical structure database
 

Interesting Facts terminology


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.


Natural Abundance

Where this element is most commonly found in nature.


Biological Roles

The elements role within the body of humans, animals and plants. Also functionality in medical advancements both today and years ago.


Appearance

The description of the element in its natural form.

Uses / Interesting Facts

 
Image explanation
An image representing Mjolnir - Thor's hammer and creator of thunder and lightning.
Appearance
A weakly radioactive, silvery metal. It is used to produce gas mantles, which on heating with a flame, quickly produce an incandescent glow.
Uses
The principal use of thorium is in the Welsbach mantle, which consists of thorium oxide amongst other compounds. This type of mantle glows with a dazzling flame when heated by gas, so is used in portable gas lights. Thorium is also an important alloying agent in magnesium, as it imparts greater strength and creep resistance at high temperatures. Thorium can be used as a source of nuclear power. It is about three times as abundant as uranium and about as abundant as lead, and there is probably more energy available from thorium than both uranium and fossil fuels. However, although work has been done in developing thorium cycle convertor-reactor systems, it will be many years before such a system is operative - if at all.
Biological role
Thorium has no known biological role. It is toxic due to its radioactivity.
Natural abundance
Thorium is found in large deposits in the USA and elsewhere, but these have not been exploited as a source of the element. Several methods are used to produce the metal, such as reducing thorium oxide with calcium and by the electrolysis of anhydrous thorium chloride.
 
Atomic Data Terminology

Atomic radius/non -bonded (Å)
Based on Van der Waals forces (where several isotopes exist, a value is presented for the most prevalent isotope). These values were calculated using a multitude of methods including crystallographic data, gas kinetic collision cross sections, critical densities, liquid state properties,for more details please refer to the CRC Handbook of Chemistry and Physics.


Electron affinity (kJ mol-1)
The energy released when an additional electron is attached to the neutral atom and a negative ion is formed (where several isotopes exist, a value is presented for the most prevalent isotope). *


Electronegativity (Pauling scale)
The degree to which an atom attracts electrons towards itself, expressed on a relative scale as a function bond dissociation energies, Ed in eV. χA - χB =(eV)-1/2sqrt(Ed(AB)-[Ed(AA)+Ed(BB)]/2), with χH set as 2.2 (where several isotopes exist, a value is presented for the most prevalent isotope).


1st Ionisation energy (kJ mol-1)
The minimum energy required to remove an electron from a neutral atom in its ground state (where several isotopes exist, a value is presented for the most prevalent isotope).


Covalent radius (Å)
The size of the atom within a covalent bond, given for typical oxidation number and coordination (where several isotopes exist, a value is presented for the most prevalent isotope). ***

Atomic Data

 
Atomic radius, non-bonded (Å) 2.450 Covalent radius (Å) 1.9
Electron affinity (kJ mol-1) Unknown Electronegativity
(Pauling scale)
1.300
Ionisation energies
(kJ mol-1)
 
1st
608.504
2nd
1148.175
3rd
1929.705
4th
2778.775
5th
-
6th
-
7th
-
8th
-
 

Mining/Sourcing Information

Data for this section of the data page has been provided by the British Geological Survey. To review the full report please click here or please look at their website here.


Key for numbers generated


Governance indicators

1 (low) = 0 to 2

2 (medium-low) = 3 to 4

3 (medium) = 5 to 6

4 (medium-high) = 7 to 8

5 (high) = 9


Reserve base distribution

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %

(Where data are unavailable an arbitrary score of 2 was allocated. For example, Be, As, Na, S, In, Cl, Ca and Ge are allocated a score of 2 since reserve base information is unavailable. Reserve base data are also unavailable for coal; however, reserve data for 2008 are available from the Energy Information Administration (EIA).)


Production Concentration

1 (low) = 0 to 30 %

2 (medium-low) = 30 to 45 %

3 (medium) = 45 to 60 %

4 (medium-high) = 60 to 75 %

5 (high) = 75 %


Crustal Abundance

1 (low) = 100 to 1000 ppm

2 (medium-low) =10 to 100 ppm

3 (medium) = 1 to 10 ppm

4 (medium-high) = 0.1 to 1 ppm

5 (high) = 0.1 ppm

(Where data are unavailable an arbitrary score of 2 was allocated. For example, He is allocated a score of 2 since crustal abundance data is unavailable.)


Explanations for terminology


Crustal Abundance (ppm)

The abundance of an element in the Earth's crust in parts-per-million (ppm) i.e. The number of atoms of this element per 1 million atoms of crust.


Sourced

The country with the largest reserve base.


Reserve Base Distribution

This is a measure of the spread of future supplies, recording the percentage of a known resource likely to be available in the intermediate future (reserve base) located in the top three countries.


Production Concentrations

This reports the percentage of an element produced in the top three countries. The higher the value, the larger risk there is to supply.


Total Governance Factor

The World Bank produces a global percentile rank of political stability. The scoring system is given below, and the values for all three production countries were summed.


Relative Supply Risk Index

The Crustal Abundance, Reserve Base Distribution, Production Concentration and Governance Factor scores are summed and then divided by 2, to provide an overall Relative Supply Risk Index.

Supply Risk

 
Scarcity factor 7.0
Country with largest reserve base Australia
Crustal abundance (ppm) 5.6
Leading producer India
Reserve base distribution (%) 24.30
Production concentration (%) 73.50
Total governance factor(production) 7
Top 3 countries (mined)
  • 1) Australia
  • 2) India
  • 3) USA
Top 3 countries (production)
  • 1) India
  • 2) Brazil
  • 3) Malaysia
 

Oxidation states/ Isotopes


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

Terminology


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. Free atoms have an oxidation state of 0, and the sum of oxidation numbers within a substance must equal the overall charge.


Important Oxidation states
The most common oxidation states of an element in its compounds.


Isotopes
Elements are defined by the number of protons in its centre (nucleus), whilst the number of neutrons present can vary. The variations in the number of neutrons will create elements of different mass which are known as isotopes.

Oxidation States / Isotopes

 
Common oxidation states 4
Isotopes Isotope Atomic mass Natural abundance (%) Half life Mode of decay
  230Th 230.033 - 7.56 x 104 α 
        > 2 x 1018 sf 
  232Th 232.038 100 1.4 x 1010 α 
        1.2 x 1021 sf 
 

Pressure and Temperature - Advanced Terminology


Molar Heat Capacity (J mol-1 K-1)

Molar heat capacity is the energy required to heat a mole of a substance by 1 K.


Young's modulus (GPa)

Young's modulus is a measure of the stiffness of a substance, that is, 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 (GPa)

The shear modulus of a material is a measure of how difficult it is to deform a material, and is given by the ratio of the shear stress to the shear strain.


Bulk modulus (GPa)

The bulk modulus is a measure of how difficult to compress a substance. Given by the ratio of the pressure on a body to the fractional decrease in volume.


Vapour Pressure (Pa)

Vapour pressure is the 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 / Temperature - Advanced

 
Molar heat capacity
(J mol-1 K-1)
27.32 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)
- - - - - 3.33
x 10-11
2.00
x 10-8
2.89
x 10-6
1.54
x 10-4
4.01
x 10-3
6.1
x 10-2
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History

In 1829, Jöns Jakob Berzelius of the Royal Karolinska Institute, Stockholm extracted thorium from a rock specimen sent to him by an amateur mineralogist who had discovered it near Brevig and realised that it had not previously been reported. The mineral turned out to be thorium silicate, and it is now known as thorite. Berzelius even produced a sample of metallic thorium by heating thorium fluoride with potassium, and confirmed it as a new metal.


The radioactivity of thorium was first demonstrated in 1898 by Gerhard Schmidt and confirmed by Marie Curie. Thorium, like uranium, survives on Earth because it has isotopes with long half-lives, such as the predominant one, thorium-232, whose half life is 14 billion years.

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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 dot com. There's more information and other episodes of Chemistry in its element on our website at chemistryworld dot org forward slash elements. 

(End promo)

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References

 
Images:  Visual Elements © Murray Robertson 2011
Mining and Sourcing data:  British Geological Survey – natural environment research council.
Text:  John Emsley Nature’s Building Blocks: An A-Z Guide to the Elements, Oxford University Press, 2nd Edition, 2011.
Additional information for platinum, gold, neodymium and dysprosium obtained from Material Value Consultancy Ltd www.matvalue.com
Data: CRC Handbook of Chemistry and Physics, CRC Press, 92nd Edition, 2011.
G. W. C. Kaye and T. H. Laby Tables of Physical and Chemical Constants, Longman, 16th Edition, 1995.
Members of the RSC can access these books through our library.