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Scandium and Yttrium
Junior Chemist
CHEM 310
Final Paper
November 18, 2008
Yttrium and Scandium Tables
Element
name
Yttrium
Density
(g/cm3)
4.472
Symbol
Y
Melting
Point (oC)
1526
Meaning of the Element’s
name
Johan Gadolin named it
after the city in Sweden,
Ytterby, where it was
found.1
Boiling
Point (oC)
3336
Crystal
Structure
hexagonal
Discovery date
1794 (the oxide, Gadolin)2
1828 (pure form, Friedrich Wöhler)3
Electronegativity
(Pauling scale)
1.22
Atomic
Radius
162
Bottom half of table1
Element
name
Scandium
Symbol
Density
(g/cm3)
2.985
Melting
Point (oC)
1541
Sc
Meaning of the Element’s
name
Lars F. Nilson named it
after Scandanavia, where
the mineral was first
identified.1
Boiling
Point (oC)
2836
Crystal
Structure
hexagonal
Discovery date
1879 (the oxide, Nilson)1
1937 (pure form, Werner Fischer, Karl
Brunger and Hans Grieneisen)3
Electronegativity
(Pauling scale)
1.36
Atomic
Radius
160
Bottom half of table1
Physical properties
The pure metal of both Sc and Y are silvery in color and are somewhat air stable, less so as
the temperature increases and less so as the surface area of the metal increases.4 Yttrium forms a
protective oxide, and thus must be heated even moreso than scandium (to about 1000 oC) to initiate
reaction.4 At room temperature, scandium metal turns a light yellow or pink color in air.1 It is not
obvious what is causing the color as Sc3+ would be expected to be colorless (white) due to the lack
of d-electrons.
Purification and Properties
The most interesting thing about these two elements is in their very convoluted discovery
and isolation. It all started with a black rock found by the mineralogist Carl Axel Arrhenius in 1787
in a Ytterby quarry.2 The rock looked like coal but was quite dense and so was considered to
contain tungsten (the densest element known at that time).1 Upon careful chemical analysis by
many chemists (see Table) this mineral yielded the ‘earth’ of all of the lanthanides as well as
scandium and yttrium.2 The simple black rock was, in fact, a very complex mixture! The
lanthanides (as well as Sc and Y) all occur in nature as the +3 oxidation state and are all similar in
size. Because of these two properties, the lanthanides, Sc and Y nearly always occur together in
nature.
Currently, the best source of the elements is by the reduction of the metal(III) fluoride with
calcium:
2 MF3 + 3 Ca
2 M + 3 CaF2
where M = Sc or Y
The pure metal of both Sc and Y are silvery in color and are somewhat air stable, less so as the
temperature increases and less so as the surface area of the metal increases.4 Yttrium forms a
protective oxide, and thus must be heated even moreso than scandium (to about 1000 oC) to initiate
reaction.4 At room temperature, scandium metal turns a light yellow or pink color in air.1 It is not
obvious what is causing the color as Sc3+ would be expected to be colorless (white) due to the lack
of d-electrons.
Chemistry
Scandium and yttrium’s behavior in air has been discussed earlier. Both metals are fairly
unreactive except when heated. Both metals react with dilute hydrochloric acid to form MCl3.5
2 M(s) + 6 HCl(aq)
2 MCl3(aq) + 3 H2(g)
where M = Sc or Y
The metals react with water slowly at room temperature, more rapidly upon heating, to form
hydrogen gas,4
2 M(s) + 6 H2O(ℓ)
2 M(OH)3(s) + 3 H2(g)
Scandium is more like aluminum than the other RE’s, being a Group IIIB transition metal
(the neutral metal has three valence electrons). Scandium(III) oxide reacts with hydroxide base just
as aluminum oxide does4,
M’2O3 + OH–
M’O(OH) + NaOH
Na3[M’(OH)6]•2H2O where M’ = Al, Sc
Both Sc and Y react readily with halogens to form MX3,5
M(s) + X2(g)
MX3(s)
where X = F, Cl, Br, or I
Unlike AlCl3, ScCl3 does not act as a Friedel-Crafts catalyst,4
R–X + ScCl3
no reaction
R
R–X + AlCl3
R+ + AlCl3X– +
H2O
+ HCl + Al salts
where R = alkyl or acyl group and X is a halogen
However scandium(III) triflate is a useful organic catalyst, made by reacting Sc2O3 with triflic
acid,1
Sc2O3 + 6 CF3SO3H
2 Sc(CF3SO3)3 + 3 H2O
As mentioned previously, the common oxidation state of Sc and Y is +3. Only scandium
can form a lower oxidation state of +2, as MIScX3, but it is not very common.4 A coordination
number of six for both Sc and Y is typical, but it can vary up to a value of nine.4 Scandium only has
one known compound with a coordination number of nine, scandium(III) triflate nonahydrate.4
Both Sc and Y have one stable isotope found naturally. Scandium’s stable isotope is 45Sc
(with 24 neutrons). Yttrium’s stable isotope is 89Y (with 50 neutrons). While there is no
commercial use of any of yttrium’s isotopes, 46Sc is used in oil refinery crackers as a tracing agent.1
Other isotopes of these elements are man-made.1
Compounds and Their Uses
Since their discovery, many uses of the compounds of scandium and yttrium have been
found. Scandium(III) oxide is used for its heat and thermal shock resistance in high temperature
systems such as ceramics.1 Yttrium(III) oxide or yttrium(III) vanadate, YVO4, doped with
europium are the most widely used yttrium compounds. These doped compounds are used as the
red phosphor in television picture tubes.1 Metal halides are often added to mercury vapor lamps to
subtly change the color. Scandium(III) iodide (ScI3) makes the light from a mercury vapor lamp
resemble sunlight. As mentioned, scandium(III) triflate (Sc(CF3SO3)3) is a useful Lewis acid in
organic synthesis as it is water-stable.1
Current Research
Much like transition metals ions, scandium(III) and yttrium(III) will coordinate to a variety
of ligands, including crown ethers, aza-crown ethers and substituted tris(3,5-pyrazolyl) methane
ligands.6, 7 These compounds are interesting because they can be used for competitive binding
studies.7 J. Okuda et. al. have found that these charged compounds also show improved catalytic
behavior towards ethylene, styrene and diene polymerization versus the neutral compounds.6 The
X-ray diffraction studies show the RE’s typical coordination number (6) as well as higher
coordination. Two compounds were particularly interesting, [Sc(CH2Si(CH3)3)3(12-crown-4)] (4)
and Y(CH2Si(CH3)3)3(12-crown-4)] (5) (shown on the next page), because of their difference in
coordination.
[Sc(CH2Si(CH3)3)3(12-crown-4)], (4)
[Y(CH2Si(CH3)3)3(12-crown-4)], (5)
Compound (5) coordinates through all four oxygen atoms of the 12-crown-4, but compound (4)
only coordinates through 3 oxygen atoms of the 12-crown-4 ligand.6
Bibliography
1
Web: Wikipedia, www.wikipedia.org (and references therein) (accessed July 2008).
2
Weeks, M. E. Discovery of the Elements; Published by the Journal of Chemical Education,
Easton, 1968; Chapter 16.
3
Marshall, J. L. Discovery of the Elements: A Search for the Fundamental Principles of the
Universe; Simon & Schuster Custom Publishing: Needham Heights, 1998; pp. 22 and 68.
4
Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. Advanced Inorganic Chemistry;
John Wiley & Sons, Inc.: New York, 1999; pp. 1108-1125.
5
Web: WebelementsTM periodic table. http://www.webelements.com (accessed July 2008).
6
Elvidge, B. R.; Arndt, S.; Zeimentz, P. M.; Spaniol, T. P.; Okuda, J. Inorg. Chem. 2005, 44,
6777-6788.
7
Tredget, C. S.; Lawrence, S. C.; Ward, B. D.; Howe, R. G.; Cowley, A. R.; Mountford, P.
Organomet. 2005, 24, 3136-3148.