Cerium was discovered in 1803 by Berzelius and Hisinger, and independently by Klaproth in the same year. It is widely used in ferrocerium lighters. Its readily forms oxide in the air and form CeO2.
History and Discovery
Cerium was discovered in 1803 by Jons Jakob Berzelius and Wilhelm Hisinger in Sweden, and independently by Martin Heinrich Klaproth in Germany in the same year. It was named by Berzelius after the dwarf planet Ceres, which was discovered two years earlier. Ceres is the name of a Roman Goddess of agriculture, crop, fertility and relationships . Berzelius and Hisinger investigated the chemical properties of the new element and successfully prepared various salts of cerium. They proposed that cerium had two oxidation states: one formed colorless salts and other formed yellowish-red ones. Klaproth named its oxide ockroite due to its yellow color. In 1825, Carl G. Mosander worked with Berzelius to prepare metallic cerium. He isolated cerium from its chloride with the help of using potassium.
|Periodic Table Classification||Group n/a
|State at 20C||Solid|
|Electron Configuration||[Xe] 4f1 5d1 6s2|
|Electron Shell||2, 8, 18, 19, 9, 2
|Density||6.70 g.cm-3 at 20°C|
|Atomic Mass||140.12 g.mol -1|
|Electronegativity according to Pauling||1.12|
Cerium is the most abundant element among all lanthanides. It is present in concentration of about 66ppm in the earth crust. It is more abundant than lead and tin. Its content in the soil varies between 2 and 150ppm, and in 1.5 parts per trillion in sea water . It is also present in minerals of the monazite (reddish brown phosphate mineral) and bastnasite (family of 3 carbonate-fluoride) groups. Cerium is easily extracted from its ores because in it is the only lanthanide that can acquire the oxidation state of +4 in an aqueous solution.
Cerium is a silvery-white metal. It is soft and can be cut with a knife. Cerium ductile in nature and its hardness and elasticity are like silver. It is present in between lanthanides and actinides in the periodic table. It is present in four allotropic forms α, β, δ and γ. Both β and γ quite stable at room temperature. α- cerium is stable below -150oC. It has high density about 8.16g/cm3. δ- cerium exist above 726oC. Cerium chemical symbol is Ce, its atomic number is 58. Cerium atomic weight is 140.116. Cerium melting point is 795OC. Its boiling point is 3443oC. Its density at room temperature is about 6.770 g/cm3. Liquid cerium is dense at atmospheric pressure than its solid form.
Cerium is tarnished when exposed to air. At 150OC, cerium readily burns in air and form pale yellow cerium (IV) oxide which is also known as ceria. With hydrogen gas it is reduced to cerium (III) oxide. It is pyrophoric (when it is ground the resulting product spontaneously catch fire). It efficiently conducts electricity. It is electropositive metal that reacts with water to form cerium (III) hydroxide and hydrogen gas. Cerium also reacts with halogens and forms trihalides. It is readily dissolved in dilute sulfuric acid and forms a colorless Ce3+ ions. Cerium is the only lanthanide element which exist in +4 oxidation state. Cerium has strong oxidizing property and oxidizes hydrochloric acid to produce chlorine gas. Cerium (IV) salts are used in cerimetry titrations .
Significance and Uses
- Cerium dioxide is used as a catalyst for the combustion of thorium dioxide.
- Cerium is used in making alloys with various metal, such as aluminum and iron. It is also used in the manufacturing of stainless steel as precipitation hardening agent.
- Cerium is used as catalyst in the reduction of nitrogen oxides to nitrogen gas.
- Cerium sulfide has replaced cadmium in red pigments for toys and household wares.
- Cerium is also used in the manufacturing of flat screen television.
- It is widely used as a catalyst to refine petroleum.
- Cerium in the form of oxides is widely used in incandescent lanterns.
- It is also used to make carbon arc lights, that are used in the motion pictures for studio lighting and projector lights.
- Cerium oxides are used to refine and polish glass surface.
- It is used as flint in cigarette and gas lighter.
- Cerium oxides in the nanopowder form is mixed in diesel fuel to reduce the emission of fumes and is also helpful in improving the overall performance of automobile engines.
Cerium is present in many household equipment including energy saver bulbs, colored television, fluorescent lamps and glasses. Cerium is dangerous in work place because the cerium gas can be inhaled with the air and prolonged exposure can lead to embolism of lung. There is no biological role of cerium, however some studies have reported that certain salts of cerium can stimulate metabolic activity of the body.
Isotopes of Cerium
Cerium has four natural isotopes 136Ce, 138Ce, 140Ce and 142Ce, and only cerium-140 is theoretically the most stable and abundant isotope. The unstable isotopes have half-lives of: 136Ce has ˃ 3.8×1016 years, 138Ce has ˃ 1.5×1014 years. 142Ce has 5×1016 years. There are thirty-five radioactive artificial isotopes of cerium, which range in atomic masses from 119 u to 157 u.
. Emsley, John (2011). Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford University Press. pp. 120–125. ISBN978-0-19-960563-7.
. Greenwood and Earnshaw, pp. 1238–9