294 | The History and Use of Our Earth’s Chemical Elements The oxide terbium peroxide has a unique formula and exhibits a very rare oxidation state
294 | The History and Use of Our Earth’s Chemical Elements The oxide terbium peroxide has a unique formula and exhibits a very rare oxidation state
for terbium that is not a whole number. It is one of the rare cases in which the valence is not
a whole integer: 4Te 3.5 + 7O 2- → Tb 4 O 3
Hazards The halogens (group VIIA) of terbium are strong irritants. Most of the compounds are
toxic and some are explosive. A vacuum or inert atmosphere must be maintained when work- ing with the metal because of its strong oxidation properties.
DYSPROSIUM SYMBOL:Dy PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:66
ATOMICMASS:162.50amu VALENCE:3 OXIDATIONSTATE:+3 NATURALSTATE:Solid ORIGINOFNAME:TheworddysprosiumwasderivedfromtheGreekworddysprositos, whichmeans“difficulttoapproach.” ISOTOPES:Thereareatotalof39isotopesofdysprosium,sevenofwhicharestable.The atomicmassofthestableisotopesrangesfrom156to164amu(atomicmassunitsor atomicweight).Theunstableisotopesofdysprosiumhavehalf-livesrangingfrom150 millisecondsto3.0×10 +6 years.Alloftheunstableisotopesareradioactiveandarepro- ducedartificially.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=28
s2,p6,d10,f10
5-O=8
s2,p6
6-P=2
s2
Properties Dysprosium is a dense (specific gravity = 8.540) metal. It is soft, and when cut with a
knife, it appears as a silvery metal that oxidizes slowly at room temperatures. The white oxide (Dy 2 O 3 ) that forms on the outside of the metal sloughs off, exposing a fresh surface of the metal for more oxidation. The oxide of dysprosium is also called dysprosia. Its melting point is 1,412°C, its boiling point is 2,567°C, and its density is 8.540g/cm 3 .
Characteristics Dysprosium, with characteristics similar to most of the other rare-earths, was difficult to
discover. Although dysprosium does not react rapidly with moist air at low temperatures, it
295 does react with water and the halogens at high temperatures. It also reacts in solutions of weak
Guide to the Elements |
acids. At low temperatures, dysprosium is strongly magnetic. AbundanceandSource
Dysprosium is the 43rd most abundant element on Earth and ranks ninth in abundance of the rare-earths found in the Earth’s crust. It is a metallic element that is usually found as an oxide (disprosia). Like most rare-earths, it is found in the minerals monazite and allanite, which are extracted from river sands of India, Africa, South America, and Australia and the beaches of Florida. It is also found in the mineral bastnasite in California.
History Dysprosium was first discovered in 1886 by the chemist, Paul-Emile Lecoq de Boisbaudran
(1838–1912) as he analyzed a sample of the newly discovered erbium oxide (element 68). Boisbaudran was able to separate erbium oxide from a small sample of a new oxide of a metal. He identified this new element as element 66 on the periodic table and called it “dispro- sium.”
CommonUses There are not many uses for dysprosium. Scientists continue to experiment with it as a
possible alloy metal (it has a high melting point) to be mixed with steel to make control rods that absorb neutrons in nuclear reactors. There are only a few commercial uses for dysprosium, such as a laser material and as a fluorescence activator for the phosphors used to produce the colors in the older TV and computer cathode ray tubes (CRTs). When combined with steel or nickel as an alloy, it makes strong magnets.
ExamplesofCompounds Dysprosium has an oxidation state of +3, which forms the Dy 3+ metallic ion that is limited
to a small group of compounds. A general example that demonstrates how the ion of dyspro-
sium combines with halogen anions follows: Dy 3+ + 3Cl 1- → DyCl 3 . Dysprosium 3+ + oxygen 2- (disprosia): 2Dy 3+ +O 2- → Dy 2 O 3 . This is a white compound that is more magnetic than iron oxide. It turns yellow when dissolved in acid.
Hazards Dysprosium nitrate [Dy 2 (NO 3 ) 3 ] is a strong oxidizing agent and will ignite when in contact
with organic material. Most dysprosium salts are toxic if ingested or inhaled. HOLMIUM
SYMBOL:Ho PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:67 ATOMICMASS:164.903amu VALENCE:3 OXIDATIONSTATE:+3 NATURALSTATE:
Solid ORIGINOFNAME:DerivedfromtheLatinwordfortheancientcitynamedHolmia(pres- ent-dayStockholm,locatedinSweden). ISOTOPES:Thereareatotalof57isotopesofholmium.Onlyoneofthese,Ho-165,issta- ble,anditistheonlyisotopefoundintheEarth’scrust.Alltheother56isotopeshave half-livesofafewmillisecondsto1.20×10 +3 years,thehalf-lifeofHo-166.
296 | The History and Use of Our Earth’s Chemical Elements
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=29
s2,p6,s10,f11
5-O=8
s2,p6
6-P=2
s2
Properties Holmium is a crystal-like, solid rare-earth with a metallic luster. It is one of the more scarce
elements of the lanthanide series. It is soft, like lead, and can be hammered and pounded into thin sheets.
Its melting point is 1,474°C, its boiling point is 2,700°C, and its density is 8.79g/cm 3 . Characteristics
Although stable at room temperatures, holmium will corrode at higher temperatures and humidity. Its oxide coating is a yellowish film that reacts slowly with water and dissolves in weak acids. Holmium has one of the highest magnetic properties of any substance, but it has little commercial use.
AbundanceandSource Holmium is the 12th most abundant of the rare-earths found in the Earth’s crust. Although
it is the 50th most abundant element on Earth, it is one of the least abundant lanthanide met- als. It is found in gadolinite and the monazite sands of South Africa and Australia and in the beach sands of Florida and the Carolinas in the United States. Monazite sand contains about a 50% mixture of the rare-earths, but only 0.05% by weight is holmium. Today, small quantities of holmium are produced by the ion-exchange process.
History In the 1800s chemists searched for new elements by fractionating the oxides of rare-earths.
Carl Gustaf Mosander’s experiments indicated that “pure” ceria ores were actually contaminated with oxides of lanthanum, a new element. Mosander also fractionated the oxides of yttria into two new elements, erbium and terbium. In 1878 J. Louis Soret (1827–1890) and Marc Delafontaine (1837–1911), through spectroscopic analysis, found evidence of the element holmium, but it was contaminated by the rare-earth dysprosia. Since they could not isolate it and were unable to separate holmium as a pure rare-earth, they did not receive credit for its discovery.
In 1879 holmium was discovered, independently, by Per Theodor Cleve (1840–1905), who managed to isolate holmium from the other rare-earths. Cleve received credit for the discovery
297 CommonUses
Guide to the Elements |
Holmium has just a few commercial uses, but it could be developed to produce items requir- ing strong permanent magnets. It is used for filaments in vacuum tubes and in electrochemistry. It is also used to help identify the atomic weights of elements by spectroscopy, which identifies the unique lines produced by each element when viewed through a spectroscope. It also has limited use as neutron absorber in nuclear reactors and as coloring agent for glass.
ExamplesofCompounds Holmium has an oxidation state of +3 that, on a limited basis, can form a few compounds
with the halogens and oxygen. They are of no commercial uses, and most holmium is used for research purposes.
Holmium chloride: Ho 3+ + Cl 1- → HoCl 3 .
Generic compounds of halogens are expressed as follows, with “X” standing for any of the
halide ions: Ho 3+ +X 1- → HoX 3 .
There is only one oxide of holmium, which sometimes is called “holmia”: the oxide (2Ho 3+ + 3O 2- → Ho 2 O 3 ) is a pale yellow solid used as a special catalyst to speed up chemical reactions and as a refractory material to line laboratory and industrial ovens.
Hazards Because holmium is produced in such very small amounts, it is not a potential hazard to
the general public. However, professional chemists take the same precautions as they do with other rare-earths.
ERBIUM SYMBOL:Er PERIOD:6 SERIESNAME:Lanthanide ATOMICNO:68
ATOMICMASS:167.259amu VALENCE:3 OXIDATIONSTATE:+3 NATURALSTATE:Solid ORIGINOFNAME:NamedforthequarryinYtterby,Sweden,whereoresandmineralsof manyelementsarefound. ISOTOPES:Thereare39isotopesoferbium,sixofwhicharestable:Er-162,Er-164,Er-166, Er-167,Er-168,andEr-170.Thesesixisotopesmakeupthetotalatomicweight(mass) oferbium,andalltheotherisotopesareartificiallymadeandshort-lived.Theirhalf-lives rangefrom200nanosecondsto49hours.
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=30
s2,p6,d10,f12
5-O=8
s2,p6