284 | The History and Use of Our Earth’s Chemical Elements Properties
284 | The History and Use of Our Earth’s Chemical Elements Properties
Neodymium is the third most abundant rare-earth element in the Earth’s crust (24 ppm). It
is reactive with moist air and tarnishes in dry air, forming a coating of Nd 3 O 3 , an oxide with
a blue tinge that flakes away, leaving bare metal that then will continue to oxidize. Its melting point is 1,021°C, its boiling point is 3,074°C, and its density is 7,01 g/cm 3 .
Characteristics As an element, neodymium is a soft silver-yellow metal. It is malleable and ductile. It can
be cut with a knife, machined, and formed into rods, sheets, powder, or ingots. Neodymium can form trivalent compounds (salts) that exhibit reddish or violet-like colors. Neodymium reacts with water to form Nd(OHO) 3 and hydrogen (H 2 ), which can explode if exposed to a flame or spark. It is shipped and stored in containers of mineral oil.
AbundanceandSource Although neodymium is the 28th most abundant element on Earth, it is third in abun-
dance of all the rare-earths. It is found in monazite, bastnasite, and allanite ores, where it is removed by heating with sulfuric acid (H 2 SO 4 ). Its main ore is monazite sand, which is a mixture of Ce, La, Th, Nd, Y, and small amounts of other rare-earths. Some monazite sands are composed of over 50% rare-earths by weight. Like most rare-earths, neodymium can be separated from other rare-earths by the ion-exchange process.
History In 1885 Carl Auer Baron van Welsbach separated a common rare-earth called didymium
into two distinct rare-earths. One he called “green didymia” (praseodymium) and the other
he named “new didymia” (neodymium). The green color of “green didymia” (praseodymium) is caused by contamination of iron.
CommonUses Misch metal is composed of about 18% neodymium, from which cigarette-lighter flints are
made. Because neodymium absorbs the yellow “sodium” line in the visible light spectrum, it can be added to glass to produce violet-, red-, or gray-colored glass. Neodymium glass is used to calibrate spectrometers and other optical devices in astronomical and laboratory observa- tion instruments. It is also used in the production of artificial rubies used in lasers. Its salts are used as pigments for ceramic enamels and glazes.
Neodymium is magnetic and is used in many of the most powerful magnets in the world. Some types of steel contain up to 18% neodymium as an alloy. It is also used as a color for TV tubes and as a tint for eyeglasses.
ExamplesofCompounds Examples of neodymiun with a +3 ion and a neodymiun ion with an oxidation state of
+8 follow:
Neodymiun (III) chloride: Nd 3+ + 3Cl 1- → NdCl 3 . Neodymium (VIII) neodymium carbide: Nd 8+ + 2C 4- → NdC 2 .
285 Neodymium oxide (Nd 2 O 3 ) is a light-blue powder used to color glass and as a pigment for
Guide to the Elements |
ceramics. It is also used to make color TV tubes. Neodymium compounds have different colors (e.g., blue, olive green, rose, and black).
Hazards Many of the compounds (salts) of neodymium are skin irritants and toxic if inhaled or
ingested. Some are explosive (e.g., neodymium nitrate [Nd(NO 3 ) 3 ]).
PROMETHIUM SYMBOL:Pm PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:61
ATOMICMASS:145amu VALENCE:2and3 OXIDATIONSTATE:+3 NATURAL STATE:Solid ORIGINOFNAME:NamedfortheGreekmythologicalgodPrometheus,whostolefire fromOlympusandgaveittohumanbeings. ISOTOPES:Thereareatotalof64isotopesofpromethiumwithhalf-livesrangingfromtwo millisecondstoover17years.Thereisnostableisotope,butPm-147withahalf-life of2.64yearsisconsideredthemoststable.Nopromethiumisfoundnaturallyinthe Earth’scrust.Allofitisproducedartificiallyfromtheleftoverresidueinnuclearreactors.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=23
s2,p6,d10,f5
5-O=8
s2,p6
6-P=2
s2
Properties Promethium is a silvery-white, radioactive metal that is recovered as a by-product of ura-
nium fission. Promethium-147 is the only isotope generally available for study. The spectral lines of promethium can be observed in the light from a distant star in the constellation Andromeda. Even so, it is not found naturally on Earth, and scientists consider it to be an artificial element. Its melting point is 1,042°C, its boiling point is estimated at 3,000°C, and
its density is 7.3 g/cm 3 . Characteristics
Promethium was the missing element in the lanthanide rare-earth series in the periodic table. Since it does not exist on Earth, it was not recovered until nuclear reactors were com- mon. Even so, scientists found it difficult to isolate it from other rare-earths.
286 | The History and Use of Our Earth’s Chemical Elements
When neodymiun-146 is bombarded with and captures neutrons, it becomes Nd-147 with
a half-life of 11 days. Through beta decay, Nd-147 then becomes Pm-147 with a half-life of
2.64 years. Other complicated neutron and beta decay reactions from these radioactive ele- ments are possible.
AbundanceandSource Promethium is not found in nature. Therefore, it is by far the least abundant on Earth:
none exists on the Earth. All of it is man-made in nuclear reactors. It is found only in the transmuted decay by-products (“ashes”) from the fission of radioactive uranium.
Promethium ( 61 Pm) was predicted to fill a space between the rare-earths neodymium ( 60 Nd) and samarium ( 62 Sm) in the periodic table in 1902. Although a few scientists claimed to have produced it, separating promethium from other rare-earths proved to be difficult, and thus identifying it was elusive. Only small amounts are produced and exist.
History The identification of promethium-147 was verified by using the mass spectrometer, which
analyzes light rays. Several radioisotopes of promethium were identified by a spectrograph, which is something like a photograph depicting the lines represented by different wavelengths of light rays. Although promethium was discovered in 1944 by Jacob A. Marinsky, Lawrence
E. Glendenin, and Charles D. Coryell (1912–1995), they did not claim its discovery until 1946. It was Coryell’s wife, Grace Mary Coryell, who suggested the name “promethium” after the Titan Prometheus, who in Greek mythology stole fire from the gods to give to mankind. Charles Coryell was the scientist who led the team working with the by-products of the decay of uranium. Such a small amount was produced in nuclear reactors that it took more than 10 years before there was evidence that element 61 actually existed, and even longer to confirm its existence. Very small amounts are produced today.
CommonUses Promethium produces beta rays (high-energy electrons). These beta rays are used to pro-
duce nuclear-powered batteries to provide electricity for spacecraft, as well as long-term usage for up to five years in regions without electricity. It also could be used as a source of portable X-rays, as a gauge to measure the thickness of various materials, and to produce special lasers that can communicate with submarines.
Promethium-147 is used in the manufacture of luminescent paint for watch dials, as well as being a source of beta rays.
ExamplesofCompounds The main oxidation state for promethium is +3. At least 30 compounds of promethium
have been identified, but none are commercially available. Three examples of typical rare-earth metal compounds are as follows:
Promethium (III) nitride: Pm 3+ +N 3- → PmN.
Promethium (III) trichloride: Pm 3+ + 3Cl 1- → PmCl 3 . Promethium (III) sesquioxide: 2Pm 3+ + 3O 2- → Pm 2 O 3 .
287 Hazards
Guide to the Elements |
Promethium is an extremely strong radiation hazard. Because it is so rare, few people will come in contact with it, but special precautions must be used when working with its isotopes.
SAMARIUM SYMBOL:Sm PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:62
ATOMICMASS:150.36amu VALENCE:2and3 OXIDATIONSTATE:+2and+3 NAT- URALSTATE:Solid ORIGINOFNAME:Itisnamedafterthemineralsamarskite. ISOTOPES:Thereare41knownisotopesofsamarium.Sevenoftheseareconsidered
stable.Sm-144makesupjust3.07%ofthenaturaloccurringsamarium,Sm-150makes up7.38%ofnaturalsamariumfoundonEarth,Sm-152constitutes26.75%,andSm- 154accountsfor22.75%.Alltheremainingisotopesareradioactiveandhaveverylong half-lives;therefore,theyareconsidered“stable.”Allthreecontributetothenaturaloccur- renceofsamarium:Sm-147=14.99%,Sm-148=11.24%,andSm-149=13.82%.
Samariumisoneofthefewelementswithseveralstableisotopesthatoccurnaturally onEarth.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
1-K=2
s2
2-L=8
s2,p6
3-M=18
s2,p6,d10
4-N=24
s2,p6,d10,f6
5-O=8