290 | The History and Use of Our Earth’s Chemical Elements process is used to extract europium from the other rare-earths found in monazite sand
290 | The History and Use of Our Earth’s Chemical Elements process is used to extract europium from the other rare-earths found in monazite sand
(ore). History
In 1896 Eugene-Anatole Demarcay (1852–1904), a French chemist, was working with a sample of samarium when he realized that it was contaminated by an unknown element. He was able to separate the two (samarium and europium) in 1901 by a long and tedious process. He is given credit for the discovery of europium and was the one to give the new element its name.
CommonUses There are only a few commercial uses for europium. Europium oxide, (Eu 2 O 3 ), a com-
pound of europium, is added to infra-sensitive phosphors to enhance the red colors on TV and computer-monitor picture tubes. It is also added to fluorescent light tubes to increase their efficiency, as well as to some materials to make lasers. Since it is a good neutron absorber, it is part of nuclear reactor control rods. Europium is an additive to the glue used on postage stamps, thus making it possible for the electronic sorting machines in U.S. postal offices to “read” the stamps.
ExamplesofCompounds Two examples of compounds using the oxidation states of 2 and 3 follow:
Europium (II) oxide: 2Eu + 3H 2 O → Eu 2 O 3 + 3H 2 . Europium (III) chloride: 2Eu + 3Cl → EuCl 3 .
Hazards Europium is very reactive and, in powder form, may burst into flames spontaneously at
room temperature. Most of the salts of europium are toxic when inhaled or ingested. GADOLINIUM
SYMBOL:Gd PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:64 ATOMICMASS:157.25amu VALENCE:3 OXIDATIONSTATE:+3 NATURALSTATE:
Solid ORIGINOFNAME:Namedforthemineralgadolinite,whichwasnamedfortheFrench
chemistJohannGadolin. ISOTOPES:Thereare39isotopesofgadolinium.Sevenofthesearestable.Theyare:Gd- 54,whichmakesup2.18%ofallthegadoliniumfoundintheEarth’scrust;Gd-55, supplying14.80%;Gd-156,makingup20.47%;Gd-157,constituting15.56%;andGd- 158,accountingfor24.85%.Inaddition,therearetwoisotopesofgadoliniumthatare radioactiveandwithsuchlonghalf-livesthattheystillexistintheEarth’scrust.Theyare regardedasstableisotopesalongwiththeotherseven.TheyareGd-152(1.08×10 +14 years),whichexistsinjust0.20%inabundance,andGd-160(1.3×10 +21 years),found in21.86%abundance.
Guide to the Elements |
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=25
s2,p6,d10,f7
5-O=9
s2,p6,d1
6-P=2
s2
Properties Gadolinium is silvery-white, soft, malleable, and ductile with a metallic luster. It is the sec-
ond of what is referred to as the dysprosium, subgroup in the middle of the lanthanide series of rare-earths. It tarnishes in air, forming the oxide (Gd 2 O 3 ) on the surface, which flakes off the surface, exposing a fresh metal that in turn oxidizes. Its melting point is 1,313°C, its boiling point is 3,273°C, and its density is 7.90g/cm 3 .
Characteristics Gadolinium, unlike most of the rare earths in the dysprosium subgroup, reacts slowly
with water, releasing hydrogen. It is strongly magnetic at low temperatures. Two of its stable isotopes (Gd-155 and Gd-157) have the greatest ability of all natural elements to absorb ther- mal neutrons to control the fission chain reaction in nuclear reactors. However, few of these isotopes are found in the ores of gadolinium.
AbundanceandSource Gadolinium is the 40th most abundant element on Earth and the sixth most abundant of
the rare-earths found in the Earth’s crust (6.4 ppm). Like many other rare-earths, gadolinium is found in monazite river sand in India and Brazil and the beach sand of Florida as well as in bastnasite ores in southern California. Similar to other rare-earths, gadolinium is recovered from its minerals by the ion-exchange process. It is also produced by nuclear fission in atomic reactors designed to produce electricity.
History In 1878 Jean-Charles Gallissard de Marignac discovered one of the “missing” rare-earths,
which he named “ytterbium.” Two years later, Marignac discovered another, which was later named “gadolinium” for Johann Gadolin, the “father of the rare-earths.” Gadolin was given this honor because he discovered the first rare-earth and, in general, described the similar chemical and physical properties of all the rare-earths.
Other chemists also worked to separate gadolinium from the mineral dydimia. Paul-Emile Locoq de Boisbaudran, following clues provided by Marignac, isolated element 62 (samarium)
292 | The History and Use of Our Earth’s Chemical Elements from dydimia in 1879. In 1886, using the same source, he was able to isolate element 64,
named in Johann’s honor. Both men are generally credited with its discovery, which was con- firmed in 1886.
CommonUses Gadolinium’s main use is based on its ability to absorb neutrons, thus making it ideal as a
neutron-shielding and neutron-absorbing metal. It is also used as an alloying agent for steel and other metals to make the metals more workable and to be able to withstand low temperatures.
Gadolinium is used in the manufacture of electronics and can be combined with yttrium to make garnets used in microwaves. Gadolinium is used as a catalyst to speed up chemical reactions, and to activate phosphor compounds in TV screens and cast filaments in electrical devices. It is also used in high-temperature furnaces. Gadolinium is paramagnetic at normal room temperatures (weaker than ferromagnetic) and becomes strongly ferromagnetic at very cold temperatures.
ExamplesofCompounds One way to produce gadolinium is by heating anhydrous gadolinium chloride with cal-
cium (e.g., 2GdCl 3 + 3Ca → 2Gd + 3CaCl 3 ). The commercial process of ion exchange is used to produce most gadolinium. Following are two examples of the +3 oxidation state of gadolinium:
Gadolinium (III) chloride: Gd 3+ + 3Cl 1- → GdCl 3 . Gadolinium (III) oxide: 2Gd 3+ + 3O 2- → Gd 2 O 3 .
Hazards The halogens of gadolinium are very toxic, and gadolinium nitrate is explosive. As with
most rare-earths, care should be taken not to inhale fumes or ingest particles of gadolinium. TERBIUM
SYMBOL:Tb PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:65 ATOMICMASS:158.925amu VALENCE:3and4 OXIDATIONSTATE:+3 NATURAL
STATE:Solid ORIGINOFNAME:NamedforavillageinSweden. ISOTOPES:Thereareatotalof52isotopesofterbium,andonlyoneoftheseisstable(Tb-
159).Terbium-59makesup100%oftheelementfoundintheEarth’scrust
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=27
s2,p6,d10,f9
5-O=8
s2,p6
6-P=2
s2,p6
293 Properties
Guide to the Elements |
There are two allotropic (crystal forms) of terbium, both of which are dependent on its temperature. The alpha ((α) form exists at room temperatures and up to temperatures of 1,298°C, and the beta (β) form exists beyond these temperatures. Although terbium is a sil- very metal that resembles aluminum and feels like lead, it is much heavier than either of these two elements. It is placed in the yttrium subgroup (lanthanide series) of the rare-earths. It is also resistant to corrosion.
Its melting point is 1,356.9°C, its boiling point is 3,230°C, and its density is 8.23g/cm 3 . Characteristics
Terbium is not found in great quantities on Earth. In fact, minerals where terbium is found contain about 0.03% terbium. Not much of the stable isotope is found as a free metal; rather most of it is mixed with other rare-earths or are in compound forms.
AbundanceandSource Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance.
Terbium can be separated from the minerals xenotime (YPO 4 ) and euxenite, a mixture of the following: (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti 2 O 6 ). It is obtained in commercial amount from monazite sand by the ion-exchange process. Monazite may contain as much as 50% rare-earth elements, and about 0.03% of this is terbium.
History
A stone quarry near the town of Ytterby in Sweden produces a large number of rare-earth elements. Carl Gustaf Mosander (1797–1858) discovered several rare-earths, including the rare-earth mineral gadolinite in this quarry in 1843. He was able to separate gadolinite into three separate, but closely related, rare-earth minerals that he named yttria (which was color- less), erbia (yellow color), and terbia (rose-colored). From these minerals, Mosander identified two new rare-earth elements, terbium and erbium. The terbia that was found was really a
compound of terbium: terbium oxide (Tb 2 O 3 )
CommonUses There are few uses for terbium. However, terbium can be used as an activator for green
phosphor in TV tubes, and some of its compounds are used to produce laser lights. It is also used to “dope” (coat) some forms of solid-state instruments, as a stabilizer in fuel cells so that they can operate at high temperatures, and as a metal for control rods in nuclear reactors.