Cerium sulfate acts like its in what physical state

The image is based on the asteroid Ceres, after which the element is named. The background is based on an early 17th-century astronomical map.

Cerium is a grey metal. It is little used because it tarnishes easily, reacts with water and burns when heated.

Cerium is the major component of mischmetal alloy (just under 50%). The best-known use for this alloy is in ‘flints’ for cigarette lighters. This is because cerium will make sparks when struck. The only other element that does this is iron.

Cerium(Ill) oxide has uses as a catalyst. It is used in the inside walls of self-cleaning ovens to prevent the build-up of cooking residues. It is also used in catalytic converters. Cerium(III) oxide nanoparticles are being studied as an additive for diesel fuel to help it burn more completely and reduce exhaust emissions.

Cerium is the most abundant of the lanthanides. It is more abundant than tin or lead and almost as abundant as zinc. It is found in a various minerals, the most common being bastnaesite and monazite.

Cerium oxide is produced by heating bastnaesite ore, and treating with hydrochloric acid. Metallic cerium can be obtained by heating cerium(III) fluoride with calcium, or by the electrolysis of molten cerium oxide.

History

History

Cerium was first identified by the Jöns Berzelius and Wilhelm Hisinger in the winter of 1803/4. Martin Klaproth independently discovered it around the same time.

Although cerium is one of the 14 lanthanoid (aka rare earth) elements it was discovered independently of them. There are some minerals that are almost exclusively cerium salts such as cerite, which is cerium silicate. A lump of this mineral had been found in 1751 by Axel Cronstedt at a mine in Vestmanland, Sweden. He sent some to Carl Scheele to analyse it but he failed to realise it was new element. In 1803, Berzelius and Hisinger examined it themselves and proved that it contained a new element.

It was not until 1875 that William Hillebrand and Thomas Norton obtained a pure specimen of cerium itself, by passing an electric current through the molten cerium chloride.

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 data

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

Oxidation states and isotopes

Oxidation states and isotopes

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

Supply risk

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

Pressure and temperature data – advanced

Podcasts

Podcasts

Chemistry in its element: cerium

You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry.

Hello, this week we're meeting the chemical that behaves badly and won't obey the rules when it comes to compounds involving oxygen and if that wasn't inflammatory enough, it is also the source of sparks that brings a lighter to life. But thankfully it's also got a softer side and that is a soothing remedy for burns, as Andrea Sella knows only too well.

A few weeks ago I had a stupid accident in the lab; I wont go into the details; I am not terribly proud about what happened. But the result is I suffered from some superficial burns on my face and neck. I was seen to by a specialist nurse who nodded at me and then handed me tub of ointment. 'Its flammacerium', she said, 'apply it twice a day'. 'Flama what', I replied, 'cerium', she said. I was delighted. 'Cerium, it can not be serious, it's my favorite element'. The nurse laughed. Fortunately she didn't ask me why, she would have never got me out of the clinic. But perhaps if she listened to this Podcast, she will find out.

Cerium is one of the first members of a series of about 14 elements with exotic and evocative names often referred to as the 'rare earths' or 'lanthanides'. The most striking thing about these elements is their remarkable chemical similarity. So much so for almost a hundred years, chemists almost went mad trying to separate them. William Crookes, the great Victorian inventor and spectroscopist wrote in 1887, 'these elements perplex us in our researches; they baffle us in our speculations and haunt us in our very dreams. They stretch like an unknown sea before us marking mystifying and murmuring strange revelations and possibilities'. Yet Cerium stands out from the crowd with its insoluble ceramic oxide, Ceria which has changed our world. But I'm, getting ahead of myself.

The discovery of cerium was an accident. Around 1800, a young geologist Wilhelm Hisinger was rock hunting on his father's estate on the island of Västmanland, in Sweden, and found a new mineral that struck him as unusually dense. Hoping that it might be an ore of the recently discovered element Tungsten, Hisinger sent a sample to that element's discoverer Carl Wilhelm Scheele who took a look and said rather unhelpfully that there was no Tungsten in it. Undeterred Hisinger went to work with the great Swedish analytical chemist theorist Jöns Jakob Berzelius. In 1803, they isolated a new metallic element that they separated, thanks to the insolubility of its oxide. The named the element after the asteroid Ceres, itself named after the Roman goddess of agriculture. At about the same time, the German analyst Martin Klaproth isolated the same element from a different Scandinavian mineral. Both reports appeared in the same journal a few months apart causing something of an academic clash over exactly who got there first. The isolation of the metal however would have to wait another 70 years until the electrolysis of molten cerium chloride.

The metal itself is nothing special to look at; it's a standard silver grey color and it tarnishes slowly in air as an oxide layer builds up on the surface. But in powdered form it is much more exciting. It is highly reactive particularly when alloyed with iron; it forms a brittle material ferrous cerium which sparks spectacularly when struck and is the basis of the flints of cigarette lighters and those exciting fire steels for chefs. Why does it burn so furiously? Well Cerium is fairly electro positive. So it will give up its outer electrons easily. And the oxide Ceria that I alluded to earlier is almost brick like in its stability. So it gives out huge amount of energies when it combusts. Ceria is also very hard which has made it a useful roche or polish for lens. If you happen to want to grind or polish your own telescope, then cerium dioxide is probably what you will use. But what makes the oxide really interesting is it misbehaves. Although the formula may appear to be CeO₂, one cerium 2 oxygens in reality the compound always has slightly less than 2 oxygens; the surface is peppered with defects, gaps where an oxygen atom should be and the degree of imperfection varies; it depends very much on how the oxide is prepared or treated. So one of the headline uses for this apparently flawed oxide is in the catalytic converters of cars and trucks. A honeycomb of cerium dioxide helps to combust un-burnt fuel coming down the exhaust pipe by releasing oxygen during the oxygen lean part of the engine's cycle while picking the oxygen back up in the rich stage. As a nanopowder, mixed in with diesel fuel, it can clean up the otherwise sooty fumes produced by trucks and buses. So Cerium is critical for reducing the impact of the internal combustion engines that power our vehicles. But if you take an even closer look at Ceria it becomes more confusing. At first sight it looks like a no-brainer. Cerium looses 4 electrons handing them over to the surrounding oxygen leaving aside defects, this means it has a 4+ oxidation state. But on very close inspection with x-ray spectroscopy its clear that the cerium hangs on to at least some of those four electrons and its true oxidation state is in a quantum mechanical limbo some where between 3 and 4. Indeed the great Japanese spectroscopist Akio Kotani once wrote that 'there is no genuine example of Cerium 4'. And as always there is mystery concealed just beneath the surface of even the most apparently simple looking chemistry. So why you might ask, is cerium a burn cream; that too is a mystery. The most that the doctors can tell me is that it seems to work. Something to which I can great fully attest.

That's UCL's Andrea Sella on cerium the element that sparks up lighters, vanishes burns and also helps us to clean up our act when it comes to pollution. Now next week it's definitely a case of don't blink, or you might miss it.

The nuclear collisions used to make them created only about one atom per hour. Yet 7 fleeting atoms of seaborgium to work with, the researches figured out that it's a metal comparable to molybdenum and tungsten. In such virtuoso experiments we can see the periodic table continuing to exert its pattern even among the elements that nature never glimpsed.

And Phil Ball will be telling us the story of those 7 atoms of seaborgium next time. I do hope you can join us. I'm Chris Smith, thanks for listening.

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.