The Lanthanides

1A 2A 3A 4A 5A 6A 7A 8A
(1) (2) (13) (14) (15) (16) (17) (18)
3B 4B 5B 6B 7B 8B 1B 2B
(3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
1 H He
2 Li Be B C N O F Ne
3 Na Mg Al Si P S Cl Ar
4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
6 Cs Ba La   Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
7 Fr Ra Ac   Rf Db Sg Bh Hs Mt Ds Rg Uub Uuq
6   Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
7   Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

 

The lanthanides , elements 58-71, follow lanthanum on the periodic table.  They have electron configurations of 4fx 5d1 6s2.  The lanthanides are all chemically very similar, since each additional electron is added to a lower-lying 4f orbital, thereby not affecting the valence shell.  Most of these elements are reactive, lustrous, silvery-white metals, and are normall found in compounds in the +3 oxidation state (from losing the 5d1 6s2 electrons), although other oxidation states are known.

Because of their chemical similarity, it is often very difficult (and expensive) to obtain the lanthanides in their pure metallic form.  They are most frequently found in monazite and monazite sand, an ore containing phosphate salts of the lanthanides [(Ce,La,Th,Nd,Y)PO4], and bastnasite and hydroxylbastnasite, which contain carbonate and fluoride salts [(Ce,La,Y)CO3F], [(Ce,La,Nd)CO3(OH,F)].  In both of these ores, lanthanum and cerium are the most abundant elements, although they contain all of the lanthanides in varying concentrations (except promethium).

The lanthanides are often used in a mixture called misch metal (German for "mixed metal"), which consists of 50% cerium, 25% lanthanum, with the other 25% comprising a mixture of the rest of the lanthanides.  This alloy is used to harden some steels, in lighter flints, and as a "getter" in vacuum to react with and remove trace gases.

 

Cerium (Ce, Z=58)

Cerium is a soft, malleable and ductile, gray metal.  It is named after the asteroid Ceres (which was named after the Roman goddess of agriculture), which had been discovered in 1801, two years before the discovery of the element, and which some astronomers believed might be large enough to be considered a planet.  It is the most abundant of the "rare earth" elements, with a concentration of 68 ppm in the Earth's crust, making it the 25th most abundant element.  It is found in the ores cerite [(La,Ce,Ca)9(Mg,Fe)(SiO4)6[(SiO3)(OH)](OH)3], allanite or orthite [(Ca,Ce,La,Y)2(Al,Fe)3(SiO4)3(OH)], rhabdophane [(Ce,La,Nd)PO4ĚH2O], and synchysite [Ca(Ce,La,Nd,Y)(CO3)2F], but its main sources are bastnasite, hydroxylbastnasite, and monazite and monazite sand (see introduction).

Cerium oxidizes in moist air, and reacts quickly in hot water.  The most common oxidation states are +3 and +4, although other oxidation state, such as +8, are also known.

Cerium(IV) oxide, CeO2, is used as an abrasive to polish glass used in lenses and CRT displays, and to extend the life of the glass and improve its color dispersion.  Cerium salts are also used in high-intensity carbon lamps.  Cerium is also used in catalytic converters where it aids in oxidizing unreacted hydrocarbons and in reducing nitrogen oxides.  Cerium(III) sulfide, Ce2S3, is being increasingly used as a red pigment in place of toxic cadmium salts.

Although cerium does not appear to play any biological role, small amounts of cerium are present in the calcium phosphate of bone.

 

Praseodymium (Pr, Z=59)

Praseodymium is a soft, malleable and ductile, silvery-white metal.  Its name is derived from the Greek words prasios and didymos, meaning "green twin."  This name was given to the element when it was realized that "didymium," an element isolated along with lanthanum from a cerium-containing ore, was actually two elements, which were rechristened as praseodymium ("green twin") and neodymium ("new twin").  Its concentration in the Earth's crust is 9.5 ppm, making it the 39th most abundant element.  It is found in the ores monazite and bastnasite (see introduction).

Praseodymium is reacts slowly in air to develop a green oxide coating; it is very reactive in water.  Its most common oxidation state is +3.

Praseodymium salts are used to make yellow-colored glass, including the yellow "didymium" glass used in welder's goggles which protects welders from infrared radiation.  It is also used in carbon electrodes for searchlights, floodlights, and the lighting used in motion picture studios.  Praseodymium is also used in magnesium alloys used in aircraft engines.  Misch metal (see introduction) contained about 5% praseodymium.

 

Neodymium (Nd, Z=60)

Neodymium is a soft, malleable and ductile, silvery-white metal.  Its name is derived from the Greek words neos and didymos, meaning "new twin."  This name was given to the element when it was realized that "didymium," an element isolated along with lanthanum from a cerium-containing ore, was actually two elements, which were rechristened as praseodymium ("green twin") and neodymium ("new twin").  It is found in the Earth's crust at a concentration of 38 ppm, making it the 27th most abundant element.  It is found chiefly in the ores monazite and bastnasaite (see introduction).

Neodymium oxidizes easily in both air and water.  In its compounds, it is usually found in the +3 oxidation state, although the +2 and +4 oxidation states also occur.

Neodymium is used to strengthen alloys of magnesium.  It is also alloyed with iron and boron to make NIB magnets, which are extremely strong permanent magnets.  (These are sometimes referred to as "rare earth magnets" or "neodymium magnets.")  Neodymium salts are used to make colored glass, ranging from violet through wine-red, and is found along with praseodymium in the protective glass in welder's goggles.  Misch metal (see introduction) contains about 18% neodymium.

 

Promethium (Pm, Z=61)

Promethium is an unstable, radioactive element which is only found on Earth in minute quantities in uranium ores.  Its existence was suspected for some time, because there was no known element with 61 protons in its nucleus, but there were no universally agreed-upon reports of its discovery until 1945, when it was isolated by researchers who were separating and purifying uranium fission products at the Oak Ridge National Laboratory in Oak Ridge, Tennessee.  It is named for the Greek god Prometheus, who stole fire from the gods and gave it to mankind, and was punished by being chained to a rock and having his liver eaten by a eagle every day.

The most stable isotope of the element, promethium-145, has a half-life of 17.7 years; promethium-146 has a half-life of only 5.53 years, while that of promethium-147 is 2.62 years.  There are a number of other isotopes as well, but the majority of them have half-lives that are less than 30 seconds.  Promethium is found in trace amounts in uranium ores, but because it is so unstable, it never accumulates above the concentration of about a picogram (10-12 g) per ton of ore.  The spectral lines of promethium have also been observed in some stars.  Promethium emits beta particles, and in the presence of elements of higher atomic weight can stimulate the release of X-rays.  It can be produced artificially by the bombardment of neodymium-146 with neutrons to form neodymium-147, which decays into promethium-147 and a beta particle.

Because promethium is so unstable, it has few practical applications, but it is used as a beta-particle emitter for thickness gauges used for measuring the thickness of sheets of steel, in some luminous blue and green paints, and in miniature batteries used in guided missiles and pacemakers.

 

Samarium (Sm, Z=62)

Samarium is a silvery metal.  It is named for the mineral samarskite, from which it was first obtained.  It is present in the Earth's crust at a concentration of 8 ppm, making it the 40th most abundant element.  It is obtained from the ore monazite (see introduction), which contains up to 3% samarium; it is also found in bastnasite.

Samarium is stable in dry air, but oxidizes in moist air, and ignites when heated to 150C.  In its compounds, it is usually found in the +2 or +3 oxidation states.  Samarium is used in alloys with cobalt to make strong permanent magnets which have a high resistance to demagnetization.  It is also used in carbon-arc lights used in motion picture studios, as a neutron absorber in nuclear reactors, and in optical glass to absorb infrared light.  Misch metal contains about 1% samarium.

 

Europium (Eu, Z=63)

Europium is a soft, silvery-white metal.  It is named for the continent of Europe.  It is found in the Earth's crust at a concentration of 2 ppm, making it the 50th most abundant element.  It is obtained from the ore monazite (see introduction), which contains up to 2.8% samarium; it is also found in bastnasite.

Europium is the most reactive of the lanthanides, oxidizing readily in air and water, and ignites when heated to 180C.  In its compounds it is usually found in the +2 or +3 oxidation state.

Europium is used as in the red phosphor in the cathode-ray tubes in TVs and computer monitors.  It is also used in fluorescent lamps to add a blue component to the light (from Eu2+), giving a more natural light.

 

Gadolinium (Gd, Z=64)

Gadolinium is a soft, ductile, silvery-white metal.  It is named for the mineral gadolinite, the first mineral containing rare earth elements to be discovered; gadolinite was in turned named after Johan Gadolin, the Swedish chemist who first investigated it.  It is found in the Earth's crust at a concentration of 8 ppm, making it the 41st most abundant element.  It is obtained from the ore monazite and bastnasite (see introduction).

Gadolinium is relatively stable in dry air, but oxidizes in moist air and dissolves in water and acids.  In its compounds, it is usually found in an oxidation state of +3.  Gadolinium has a greater ability to absorb neutrons than any other element, primarily in the isotopes Gd-155 and Gd-157.  It is magnetic.  It is used in alloys with steel to improve its workability and make it more resistant to oxidation at high temperatures.  Gadolinium alloys are used in making magnets that are used in many electronic devices, such as video recorders, magnetic disk drives, and compact disks.  Gadolinium compounds are used as contrast agents in magnetic resonance imaging to enhance the contrast between various tissues, making cancers easier to detect.  Gadolinium has a very high capacity for absorbing thermal neutrons, which makes it ideal for use in control rods in nuclear power generators; gadolinium oxide is mixed with the uranium fuel pellets in nuclear reactors at a concentration of about 5%.

 

Terbium (Tb, Z=65)

Terbium is a soft, ductile, silver-gray metal.  It is named after the Swedish village of Ytterby, as were yttrium, erbium, and ytterbium.  It is found in the Earth's crust at a concentration of 1 ppm, making it the 57th most abundant element.  It is obtained from the ore monazite (see introduction), which contains about 0.05% terbium; it is also found in bastnasite, which contains about 0.02% terbium.

Terbium oxidizes very slowly in air, and dissolves in water.  In its compounds, it is usually found in the +3 oxidation state.  Terbium is used to make magnetorestrictive alloys, which lengthen or shorten when exposed to a magnetic field.  Terbium is used is solid-state devices and lasers.  Its oxide is used in green phosphors in cathode-ray tubes and fluorescent lamps.

 

Dysprosium (Dy, Z=66)

Dysprosium is a soft, silvery metal.  It is named for the Greek word dysprositos, which means "hard to get at," because the first sample of the element was obtained from impure holmium oxide after a laborious sequence of dissolution in acid and precipitation with ammonia.  It is found in the Earth's crust at a concentration of 6 ppm, making it the 42nd most abundant element.  It is found in the ores monazite and bastnasite (see introduction).

Dysprosium is moderately reactive, and oxidizes in air and dissolves quickly in cold water.  In its compounds, it is usually found in the +3 oxidation state.  Because dysprosium is one of the most strongly magnetic elements, it is used in the manufacture of some permanent magnets.  In the form of dysprosium ioside, DyI3, it is used in halogen lamps to generate light that appears light white light.  Dysprosium is also used to absorb neutrons in nuclear reactors, and in dosimeters for measuring exposure to radiation.

 

Holmium (Ho, Z=67)

Holmium is a soft, malleable, silvery metal.  It is named for Holmia, the Latini name for Stockholm, Sweden.  It is found in the Earth's crust at a concentration of 1.4 ppm, making it the 55th most abundant element.  It is obtained from the ore monazite (see introduction), which contains up to 0.5% samarium; it is also found in bastnasite.

Holmium is fairly unreactive, but it oxidizes slowly in air and water, and dissolves in acids.  In its compounds, it is usually found in the +3 oxidation state.  Because holmium is one of the most strongly magnetic elements, it is used in the manufacture of some permanent magnets.

 

Erbium (Er, Z=68)

Erbium is a soft, malleable, silvery metal.  It is named after the Swedish village of Ytterby, as were yttrium, terbium, and ytterbium.  named for the Swedish town Ytterby.  It is obtained from the ore monazite and bastnasite (see introduction), as well as xenotime [ytrium phosphate, YPO4, with some trace elements] and euxenite [(Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6].

Erbium reacts very slowly with oxygen and water.  In its compounds, it is usually found in the +3 oxidation state.  Erbium is used in some safety glasses to absorb infrared light.  Erbium oxide, Eb2O3, is used to give a pink color to glass and porcelain.

 

Thulium (Tm, Z=69)

Thulium is a soft, malleable and ductile, silvery metal.  It is named for Thule, the ancient word for Scandinavia.  It is found in the Earth's crust at a concentration of 0.50 ppm, making it the 61st most abundant element.  It is obtained from the ore monazite (see introduction), which contains about 0.002% thulium; it is also found in bastnasite, which contains about 0.0008% thulium.

Thulium tarnishes in air very slowly.  In its compounds it is usually found in the +3 oxidation state.  Thulium is used in some radiation dosimeters.

 

Ytterbium (Yb, Z=70)

Ytterbium is s malleable and ductile, silvery metal.  It is named after the Swedish village of Ytterby, as were yttrium, terbium, and yttrium.  It is found in the Earth's crust at a concentration of 3 ppm, making it the 43 most abundant element.  It is obtained from the ore monazite (see introduction), which contains about 0.1% ytterbium; it is also found in bastnasite, which contains about 0.0006% ytterbium.

Ytterbium oxidizes slowly in air, but unlike most of the other transition metals, the oxide does not flake off the surface, but forms a protective layer that serves as a barrier to further oxidation.  In its compounds, it is usually found in the +3 oxidation state.  Ytterbium is used as an alloying agent in some stainless steels used in dental tools. 

 

Lutetium (Lu, Z=71)

Lutetium is a silvery-white, hard, dense metal.  It is named for Lutecia, the ancient word for Paris.  It is found in the Earth's crust at a concentration of 0.5 ppm, making it the 60th most abundant element.  It is obtained from the ore monazite (see introduction), which contains about 0.003% lutetium.  Because of its rarity, and the difficulty in separating lutetium from other elements, lutetium metal is very expensive — almost six times the price of gold and platinum.

Lutetium, unlike most of the lanthanides, is resistant to oxidation in air.  In its compounds it is usually found in the +3 oxidation state.  Lutetium compounds are used as catalysts in the cracking of petroleum, and in detectors for positron emission tomography (PET).

 

 

References

John Emsley, The Elements, 3rd edition.  Oxford:  Clarendon Press, 1998.

John Emsley, Nature's Building Blocks:  An Z-Z Guide to the Elements.  Oxford:  Oxford University Press, 2001.

David L. Heiserman, Exploring Chemical Elements and their Compounds.  New York:  TAB Books, 1992.