Encyclopedia of the Alkaline Earth Compounds

1186 Pages·2013·15.92 MB·English

by  Richard C. Ropp (Auth.)

ENCYCLOPEDIA
OF THE ALKALINE
EARTH
COMPOUNDS
R. C. R
OPP
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This book isdedicatedto my wife,
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moreyears than I wishto remember.
Preface
Thisbookisdesignedtodocumentallofthealkaline succinctly was known about a particular alkaline earth
earth compounds known to date in the scientific litera- compound and added references. Since his description
ture. It is a reference book intended to bring together, was based upon the compilation and personal assess-
in an organized fashion, information difficult to find, ment of what several authors had published in the
or dispersed in many published journals and books. past, just one compound required 6–8 citations. Many
Many of these references are obscure and not easily compounds required 8–10 references and sometimes
discovered except by persistent searching. This is the even more. Therefore, the decision was made not to
mainvalueofthiscontent.Assuch,thepreviouslypub- include citations because the reference pages would
lishedsubjectmatterhasbeenthesourceofinformation consume a large part of the book. If the reader wishes
presented here. The author has assembled results and to ascertain which authors discovered the properties of
conclusions, published by various researchers in the a particular compound, a good starting point is the
open literature, regarding a particular compound. He Internet.
then used his personal knowledge and experience to Concerningfigures,theauthorhasdrawnallofthese,
discuss various viewpoints and judgments reached by starting with figures published within various articles
various authors concerning the physical and chemical andbooks.Inmanycases,morethanoneauthor(s)pub-
properties for each compound presented within this lished essentially the same result, each a refinement of
volume.Thereaderthenhasastartingpointconcerning the previous one. The author then formed the figure
whether a particular compound is known to exist and (such as a crystal structure) according to the latest
what properties it may exhibit. Although there are results known to date. For example, the author redrew
many other resources for inorganic compounds like many phase diagrams which were not complete and
the Wiley encyclopedia, Scifinder, Scopus/Scirus, the added known data to complete the diagram. Because
Gmelin Handbooks, PubMed, Springer/Link, the mostofthefigureshadseveralcontributors,nocitations
NIMS Materials database and the Web of Science, they havebeenincludedsincethey,liketheinformationpre-
cover a vast multitude of compounds and are, in some sentedforeachcompound,wouldconsume aconsider-
cases, difficult to access. In contrast, the present book able space within themanuscript.
islimitedtoalkalineearthcompounds.Thisisthemajor Mostofthetablesarecompilationsofpreviouslypub-
worth of the bookda place to determine what alkaline lished data derived from books and journals. For
earth compounds areknown to exist. example, some tables present unit-cell occupancies for
However, the reader will soon discover that refer- a specific crystal structure. These were derived from
ences to the literature, including tables, drawings and the literature but have many authors. No specific cita-
figures, are not given. There is a good reason for this. tions arepresentedfor these tables aswell.
Earlyinthewritingofthemanuscript,theauthorassem-
bled known data and results published as papers and
books in the open literature. He then described R.C. Ropp -October 2012
xi
C H A P T E R
1
The Alkaline Earths as Metals
O U T L I N E
1.1. General Properties 1 1.2.3. Calcium 12
1.2.4. Strontium 15
1.2. Propertiesof theAlkaline Earth
1.2.5. Barium 18
Metals 4
1.2.6. Radium 19
1.2.1. Beryllium 4
1.2.2. Magnesium 8
The alkaline earth metals comprise Group 2 of the 1.1. GENERAL PROPERTIES
periodic table and include the elements Be, Mg, Ca, Sr,
Ba and Ra. These metals form cations with a formal Like other groups, the members of this family show
chargeofþ2insolutionandarethesecondmostelectro- specific patterns in their electron configuration, espe-
positive metals of all of the elements (the alkali metals cially the outermost shells, that results in trends in
are the most electropositive). The name of this specific chemical behavior (Table1.1).
groupintheperiodictablestemsfromthefactthattheir Another way to depict the electronic structure of
oxides produce basic alkaline solutions and that these these elements isshown inTable 1.2.
elements melt at such high temperatures that they Allofthealkalineearthmetalshavetwoelectronsin
remain solid (earths) in fires. The alkaline earth metals their outer valence shell, so the energetically preferred
provide a good example of group trends in chemical state of achieving a filled electron shell is to lose two
propertieswithintheperiodictable,withwell-character- electronstoformdoublychargedcations,M2þ.Thealka-
izedhomologousbehaviorasonegoesdownthegroup. lineearthmetalsaresilver-colored,softmetalsthatreact
With the exception of Be and Mg, the metals have readilywithhalogenstoformionicsalts.Theyalsoreact
a distinguishable flame color, orange-red for Ca, withwater,thoughnotasrapidlyasthealkalimetals,to
magenta-redforSr,greenforBaandcrimson-redforRa. form strongly alkaline (basic) hydroxides. Forexample,
TABLE1.1 TABLE1.2
Z Element No.ofelectrons/shell Element Symbol Electronicconfiguration
4 Beryllium 2,2 Beryllium Be [He]2s2
12 Magnesium 2,8,2 Magnesium Mg [Ne]3s2
20 Calcium 2,8,8,2 Calcium Ca [Ar]4s2
38 Strontium 2,8,18,8,2 Strontium Sr [Kr]5s2
56 Barium 2,8,18,18,8,2 Barium Ba [Xe]6s2
88 Radium 2,8,18,32,18,8,2 Radium Ra [Rn]7s2
EncyclopediaoftheAlkalineEarthCompounds
http://dx.doi.org/10.1016/B978-0-444-59550-8.00001-6 1 Copyright(cid:1)2013ElsevierB.V.Allrightsreserved.
2
1. THEALKALINEEARTHSASMETALS
whereas Na and K react with water at room tempera- TheseelementsareallfoundintheEarth’scrust,but
ture,MgreactsonlywithsteamandCawithhotwater: not in the elemental form because they are so reactive.
Instead, they are widely distributed in rock structures.
MgðsolidÞþ2 H OðgasÞ
2 The main minerals in which magnesium is found are
0 MgðOHÞ ðsolidÞþH ðgasÞ
2 2 “Carnellite”, “Magnesite” and “Dolomite”. Calcium is
Be is an exception. It does not react with water or foundin“Chalk”,“Limestone”,“Gypsum”and“Anhy-
steam,and its halidesarecovalent. drite”.Magnesiumistheeighthmostabundantelement
Thealkalineearthmetalsarenamedaftertheiroxides, in the Earth’s crust, and calciumis thefifth.
the alkaline earths, whose old-fashioned names were Some of the physical properties of the alkaline earth
Beryllia, Magnesia, Lime, Strontia and Baryta. “Earth” metalsare shown in Table1.3.
istheoldtermappliedbyearlychemiststononmetallic The metals of Group 2 are harder and denser than
substancesthatwereinsolubleinwaterandresistantto sodiumandpotassium,andhavehighermeltingpoints.
heating, properties shared by these oxides. The realiza- These properties are due largely to the presence of two
tionthattheseearthswerenotelementsbutcompounds valenceelectronsoneachatom,whichleadstostronger
is attributed to the chemist Antoine Lavoisier. In his metallic bondingthan occurs inGroup1.
“Traite´ E´lementaire de Chemie” (Elements of Chemistry) Three of these elements give characteristic colors
of 1789, he called them “salt-forming” earth elements. whenheated ina flame:
Later, he suggested that the alkaline earths might be
metaloxides,butadmittedthatthiswasmereconjecture. Mg ¼ brilliant white Ca ¼ brick(cid:2)red
In 1808, acting on Lavoisier’s idea, Humphrey Davy Sr ¼ crimson
becamethefirsttoobtainsamplesofthemetalsbyelec-
Inalltheircompounds,thesemetalshaveanoxidation
trolysisoftheirmolten“earths”.
numberofþ2and,withfewexceptions,theircompounds
If the alkaline earths are compared to the alkalis,
are ionic in nature. The reason for this can be seen by
many similarities are apparent. The main difference is
theelectronconfiguration,whichisns2foralkalineearth examinationoftheelectronconfiguration,whichalways
metals and ns1 for alkali metals. But for the alkaline hastwoelectronsinanouterquantumlevel.Theseelec-
trons are relatively easy to remove, but removing the
earth metals, the nucleus also contains an additional
thirdelectronismuchmoredifficult,asitisclosetothe
positivecharge.Also,theelementsofGroup2(alkaline
nucleus and in a filled quantum shell. This results in
earths) have much higher melting points and boiling
the formation of M2þ. The ionization energies reflect
points compared to those of Group 1 (alkali metals).
thiselectronarrangement.Thefirsttwoionizationener-
The alkalis are softer and more lightweight than the
giesarerelativelylow,andthethirdverymuchhigher.
alkaline earth metals that aremuch harderand denser.
In general, the chemical properties of Group 2
Thesecondvalenceelectronisveryimportantwhenit
elements are dominated by the strong reducing power
comesto comparing chemical propertiesof the alkaline
ofthemetals.Theelementsbecomeincreasinglyelectro-
earthandthealkalimetals.Thesecondvalenceelectron
positive as one descends within the Group. In direct
is in the same “sublevel” as the first valence electron.
contactwithoxygenorchlorinegas,littleornoreaction
Therefore, the Z is much greater. This means that the
eff
occurs. However, once started, the reactions with
elements of Group 2 have a smaller atomic radius and
oxygenand chlorinearevigorous:
much higher ionization energy than those of Group 1.
EventhoughtheGroup2containsamuchhigherioniza-
2MgðsolidÞþO ðgÞ 0 2MgOðsolidÞþheat
tionenergy,theystillformioniccompoundscontaining 2
2þ cations. Beryllium, however, behaves differently. CaðsolidÞþCl ðgasÞ 0 CaCl ðsolidÞþheat
2 2
This isdue to the fact that in orderto remove two elec-
trons from this particular atom, significantly more All the metals except beryllium form oxide layers in
energy is required. It never forms the Be2þ cation and air at room temperature that dulls the surface of the
its bondsare polarcovalent. metal. Barium is so reactive that it is stored under oil.
Atomic and ionic radii increase smoothly down the All of the metals except beryllium reduce water and
Group.Theionicradiiareallmuchsmallerthanthecor- dilute acids to hydrogen:
responding atomic radii. This arises because the atom
contains two electrons in an s level relatively far from MgðsolidÞþ2HþðaqÞ 0 MgðaqÞþH ðgasÞ
2
the nucleus. It is these electrons that are removed to
form the ion. Remaining electrons are thus in levels Magnesiumreactsonlyslowlywithwaterunlessthe
closertothenucleus,andinadditiontheincreasedeffec- waterisboiling,butcalciumreactsrapidlyevenatroom
tive nuclear charge attracts the electrons toward the temperature, and forms a cloudy white suspension of
nucleusand decreasesthe sizeof the ion. sparingly solublecalciumhydroxide.
3
1.1. GENERALPROPERTIES
TABLE1.3
Element Atomicnumber Relativeatomicmass Meltingpoint,(cid:3)C Densityinkgm/m3
Be 4 9.012 1551 1847.7
Mg 12 24.31 922 1738
Ca 20 40.08 1112 1550
Sr 38 87.62 1042 2540
Ba 56 137.33 1002 3594
IonizationenergiesinkJ/mol
1st 2nd 3rd
Be 899.4 1757.1 14,848
Mg 737.7 1450.7 7732.6
Ca 589.7 1145 4910
Sr 549.5 1064.2 4210
Ba 502.8 965.1 3600
Standardelectrode
Atomicradius/A˚ Ionicradius/A˚ (M2D) potentials/V
Be 1.13 0.34 (cid:2)1.85
Mg 1.60 0.78 2.36
Ca 1.97 1.06 (cid:2)2.87
Sr 2.15 1.27 (cid:2)2.89
Ba 2.17 1.43 (cid:2)2.90
Calcium,strontiumandbariumcanreducehydrogen Calcium hydroxide is known as “slaked lime”. It is
gas when heated,forming the hydride: sparinglysolubleinwaterandtheresultingmildlyalka-
line solution is known as “limewater” which is used to
CaðsolidÞþH ðgasÞ 0 CaH ðsolidÞ
2 2 test for the acidic gas, carbon dioxide.
The Group 2 halides are normally found in the
The hot metals are also sufficiently strong reducing
hydratedform.Theyareallionicexceptberylliumchlo-
agents to reducenitrogen gas and form nitrides:
ride. Anhydrous calcium chloride has such a strong
3MgðsolidÞþN ðgasÞ 0 Mg N ðsolidÞ affinity for water that it isused as a drying agent.
2 3 2
Of the elements in this Group only magnesium is
Magnesiumcanreduce,andburn,incarbondioxide:
producedon a largescale. It isextracted fromseawater
2MgðsolidÞþCO ðgasÞ 0 2MgOðsolidÞþCðsolidÞ bytheadditionofcalciumhydroxide,whichprecipitates
2
out the less soluble magnesium hydroxide. This
This means that magnesium fires cannot be extin- hydroxide is then converted to the chloride with HCl,
guished usingcarbondioxidefireextinguishers. which is electrolyzed in a “Downs Cell” to extract
The oxides of alkaline earth metals are normally magnesium metal. The metal is used in flares, tracer
prepared by heating the hydroxide or carbonate to bulletsandincendiarybombsasitburnswithabrilliant
release carbon dioxide gas. They have high lattice white light. It has also been alloyed with aluminum to
enthalpies and melting points. Peroxides, MO2, are produce a low-density, strong material used in aircraft.
known for all these elements except beryllium. It Magnesium oxide has such a high melting point that it
appearsthattheBe2þcationistoosmalltoaccommodate isused to line furnaces.
theperoxide anion. The alkaline earth elements are found in all living
Calcium, strontium and barium oxides react with organisms.However,beryllium’slowaqueoussolubility
water to form hydroxides: means that it is rarely available to biological systems.
That is, it has no known role in living organisms. It is
CaOðsolidÞþH OðliqÞ 0 CaðOHÞ ðsolidÞ
2 2 generally highly toxic if encountered by them.
4
1. THEALKALINEEARTHSASMETALS
In contrast, magnesium and calcium are ubiquitous TABLE1.4
and essential to all known living organisms. These
Location ppbbyweight ppbbyatoms
elements are involved in more than one role. For
example, Mg/Ca ion pumps play a pivotal role in Universe 1 0.1
some cellular processes, where magnesium functions
Sun 0.1 0.01
astheactivecenterinsomeenzymes,whilecalciumsalts
Meteorite(carbonaceous) 30 70
take a structural role(e.g. bones and teeth) in animals.
Strontium and barium display a lower availability in Crustalrocks 4900 4300
the biosphere. Strontium plays an important role in
Seawater 0.0006 0.00041
marineaquaticlife,especiallyhardcorals.Theyusestron-
Streams 0.1 0.01
tiumtobuildtheirexoskeleton.Theseelementsalsohave
some uses in medicine, for example “barium meals” in Humans 0.4 0.3
radio graphic imaging, while strontium compounds are
employedinsometoothpastes. Radiumhasa lowavail-
abilityandishighlyradioactive,makingittoxictolife. susceptible persons. The author has had direct contact
with such persons who present skeletal aspects of facial
appearanceandtorsoasthediseaseprogresses.
1.2. PROPERTIES OF THE ALKALINE
BerylliumisarelativelyrareelementinboththeEarth
EARTH METALS
and the Universe because it is not formed in conven-
tional stellar nucleosynthesis. It more accurately was
Eachofthesemetalsdisplayspecificpropertieswhich formedduringthe“BigBang”,andlaterfromtheaction
differfromtheothersbuthavesomecharacteristicsthat of cosmicrays on interstellardust.
arenearly the same. The abundanceof beryllium isshown in Table1.4.
The beryllium content of the earth’s surface rocks is
about 4–6ppm. Beryllium is a constituent in about 100
1.2.1. Beryllium
out of about 4000 known minerals, the most important
The name beryllium comes from the Greek word for of which are “Bertrandite” (Be Si O (OH) ), “Beryl”
4 2 7 2
be´rullos, beryl, and from the Prakrit veruliya, in allusion (Al Be Si O ), “Crysoberyl” (Al BeO ), and “Phena-
2 3 6 18 2 4
“to become pale”, in reference to the pale semiprecious kite”(Be SiO ).Preciousstoneformsofberylare“Aqua-
2 4
gemstone “Beryl”. For about 160 years, beryllium was marine”, “Bixbite” and “Emerald”.
alsoknownasglucinium(withtheaccompanyingchem- Berylliumhasoneofthehighestmeltingpointsofany
ical symbol Gl), the name coming from the Greek word of the light metals. It has exceptional elastic rigidity
for“sweet”,duetothesweettasteofitssalts.Abivalent (Young’smodulus¼316GPa).Themodulusofelasticity
element, beryllium is found in nature as a combination of beryllium is approximately 50% greater than that of
with other elements in minerals. Notable gemstones steel.Thecombinationofthismodulusplusberyllium’s
which contain beryllium include “Beryl” (Aquamarine, relativelylowdensitygivesitanunusuallyfastconduc-
Emerald) and “Crysoberyl”. The free element is a steel- tionofsoundatstandardconditions(about12.9km/s).
gray, strong, lightweight, brittle, alkaline earth metal Other significant properties are the high values for
with an atomic weight of 9.01218g/mol. It is primarily specific heat (1925J/kgK) and thermal conductivity
used as a hardening agent in alloys, notably beryllium– (216W/mK). This makes beryllium the metal with the
copper. Structurally, beryllium’s very low density bestheatdissipationcharacteristicsperunitweightofall
(cid:3)
(1.85 times that of water), high melting point (1278 C), ofthemetals.Incombinationwiththerelativelylowcoef-
hightemperaturestability,andlowcoefficientofthermal ficientoflinearthermalexpansion(11.4(cid:4)10(cid:2)6/K), these
expansion, make it in many ways an ideal aerospace characteristics ensure that beryllium demonstrates
material, and it has been used in rocket nozzles and is a unique degree of dimensional stability when heated.
a significant component of future-planned space tele- At STP (standard temperature and pressure), beryllium
scopes. Because of its relatively high transparency to resistsoxidationwhenexposedtoair(itsabilitytoscratch
X-rays and other ionizing radiation types, beryllium glass is due to the formation of a thin layer of the hard
metal also has a number of uses as filters and windows oxideBeO).ItalsoresistscorrosionbyconcentratedHNO .
3
forradiationandparticlephysicsexperiments. Berylliumhasalargescatteringcrosssectionforhigh-
Commercialuseofberylliummetalpresentstechnical energyneutrons,thuseffectivelyslowingtheneutronsto
challengesduetothetoxicity(especiallybyinhalation)of the thermal energy range where the cross section is low
beryllium-containing dusts. Beryllium produces a direct (0.008b). The predominant beryllium isotope, 9Be, also
corrosiveeffecttohumantissue,andcancauseachronic undergoesa(n,2n)neutronreactiontoform8Be,i.e.beryl-
life-threatening allergic disease called “Berylliosis” in liumisaneutronmultiplier,releasingmoreneutronsthan
5
1.2. PROPERTIESOFTHEALKALINEEARTHMETALS
TABLE1.5 triple-alpha process in helium-fueled stars where more
synthesistimeisavailable.7Bedecaysbyelectroncapture.
Knownisotopesofberyllium
Therefore, its decay rate is dependent upon its electron
Nuclide Z N Isotopicmass Half-life Decaymode configurationdarareoccurrenceinnucleardecay.
5Be 4 1 5.04079 Nodataavailable Protonemission Theshortest-livedknownisotopeofberylliumis13Be
whichdecaysthroughneutronemission.Ithasahalf-life
6Be 4 2 6.019726 4.06848(cid:4)10(cid:2)21s Alphadecay of 2.7(cid:4)10(cid:2)21s. 6Be is also very short lived with a half-
[0.092MeV] life of 4.96(cid:4)10(cid:2)21s. The exotic isotopes 11Be and 14Be
7Be 4 3 7.01692983 53.22days Electroncapture areknown to exhibit a“nuclearhalo”.
8Be 4 4 8.00530510 6.72206(cid:4)10(cid:2)17s Alphadecay Beryllium has the electronic configuration [He]2s2
[6.8eV] and exhibits only the þ2 oxidation state. The only
9Be 4 5 9.0121822 Stable Stable evidence of a lower valence state of beryllium is in the
factthatBeissolubleinBeCl .Thesmallatomicradius
10Be 4 6 10.0135338 1.51(cid:4)106years b-minusdecay ensures that the Be2þ ion is2highly polarizing, a fact
11Be 4 7 11.021658 13.81s b-minusdecay leading to significant covalent character in beryllium’s
12Be 4 8 12.026921 21.31ms b-minusdecay bondingwithinvariouscompounds.Berylliumis4coor-
dinateincomplexese.g.[Be(H O) ]2þandtetrahalober-
12Be 4 8 12.026921 2.71(cid:4)10(cid:2)21s Neutron yllates, BeX2(cid:2). This characteris2tic4is used in analytical
emission 4
techniques for determining Be using EDTA as a ligand
14Be 4 10 14.04289 4.84ms b-minusdecay which preferentially forms octahedral complexes, thus
15Be 4 11 15.05346 <200ns Nodata absorbingothercationssuchasAl3þwhichmightinter-
fere in the solvent extraction of a complex formed
16Be 4 12 16.06192 <200ns Nodata betweenBe2þand acetylacetone.
Beryllium metal lies above aluminum in the electro-
it absorbs. Beryllium is highly permeable to X-rays and chemical series and would be expected to be a reactive
neutronsareliberatedwhenitisstruckbyalphaparticles. metal. However it is passivated by an oxide layer and
Ofberyllium’sisotopes,only9Beisstableandtheothers does not react with air or water even at red heat. Once
arerelativelyunstableorrare.Itisthusa“mono-nuclide” ignitedhowever,berylliumburnsbrilliantlyinairform-
element. “Cosmogenic” 10Be is produced in the atmo- ing a mixtureof BeOand Be N .
3 2
spherebycosmicray spallationofoxygenand nitrogen. Beryllium dissolves readily in nonoxidizing acids,
Cosmogenic 10Be accumulates at the soil surface, where such as HCl and H SO , but not in nitric acid as this
2 4
its relatively long half-life (1.51 million years) permits forms the oxide on the surface of the metal. This
a long residence timebefore decayingto9Be.Thus, 10Be behavior is similar to that of aluminum metal. Another
and its daughter products have been used to examine strange feature is that Be is amphoteric. This means
soilerosionandsoilformationfrom“regolith”(whichis that it has the properties of both an acid and a base.
soilformedbymaterialoriginatingthroughrockweath- The following two reactions show this factor:
eringorplantgrowth),thedevelopmentoflateriticsoils BeðOHÞ ðsolidÞþH SO ðaqÞ 0 BeSO ðsolidÞ
as well as variations in solar activity, and the age of ice 2 2 4 4
cores. Solar activity is inversely correlated with 10Be þ2H2OðliqÞ
production,becausethesolarwinddecreasesthefluxof BeðOHÞ ðsolidÞþ2NaOHðaqÞ 0 Na BeðOHÞ ðaqÞ
2 2 4
galacticcosmicrayswhichreachtheEarth(Table1.5).
Beryllium-10 is also formed in nuclearexplosionsby 5 2NaþðaqÞþBeðOHÞ24(cid:2)ðaqÞ
areactionoffastneutronswith13Cinthecarbondioxide
in air, and is one of the historical indicators of past Beryllium, again similarly to aluminum, dissolves in
activity at nuclear test sites. warm alkali to form the berylliate anion, Be(OH)2(cid:2)
4
The fact that 7Be and 8Be are unstable has profound andhydrogengas.Thesolutionsofsalts,e.g.beryllium
cosmological consequences as it means that elements sulfate and beryllium nitrate are acidic because of
heavier than beryllium could not have been produced hydrolysisof the [Be(H O) ]2þ ion. Forexample:
2 4
bynuclearfusioninthe“BigBang”sincetherewasinsuf-
ficienttimeduringthenucleosynthesisphaseoftheBig BeSO ðsolidÞþ4H OðliqÞ 0 ½BeðH OÞ (cid:5)2þðaqÞ
4 2 2 4
Bang expansion to produce carbon by fusion of 4He þSO2(cid:2)ðaqÞ
nuclei. The other factor was the relatively low concent- 4
rations of 8Be available because of its short half-life. ½BeðH OÞ (cid:5)2þðaqÞþH O 0 ½BeðH OÞ ðOHÞ(cid:5)þðaqÞ
2 4 2 2 3
Astronomer Fred Hoyle first showed that the energy þH OþðaqÞ
levels of 8Be and 12C allow carbon production by a 3
6
1. THEALKALINEEARTHSASMETALS
The hydrolytic reactions of beryllium(II) ions have Althoughemeraldsandberylwereknowntoancient
(cid:3)
been calorimetrically studied at 25 C in aqueous solu- civilizations, they were first recognized as the same
tion and dioxane–water mixtures, both containing mineral (Be Al (SiO ) ) by Abbe´ Hau¨y in 1798. Later
3 2 3 6
3.0mol/dm3 Li ClO as a constant ionic medium. On that year, Louis-Nicholas Vauquelin, a French chemist,
2 4
the basis of the formation constants determined, the discovered that an unknown element was present in
enthalpyand entropy changes for thereaction: emeralds and beryl. Attempts to isolate the new
element finally succeeded in 1828 when two chemists,
xBe2þþyH O 0 ðBe ðOHÞ Þ2ðx(cid:2)yÞþþyHþ; Friedrich Wo¨lhler of Germany and A. Bussy of France,
2 x y
independently produced beryllium by reducing beryl-
were estimated for the Be2OH3þ and Be3(OH)33þ lium chloride (BeCl2) with potassium metal in a plat-
complexes in aqueous solution and 0.1mol fraction inum crucible. Today, beryllium is primarily obtained
daniodxaBnee2(–OwHat)e22rþ mcoimxtpulreexeasndinf0o.r2mBeo2lOfHra3cþti,onBed3(iOoxHan)33eþ–, f(r4oBmeOt$h2eSmiOi2n$eHra2lOs)Betrhyrlo(uBgeh3Ala2(SciOhe3)m6)icaanldpBreorctreasnsdioter
water mixture. The enthalpy and entropy changes of throughtheelectrolysisofamixtureofmoltenberyllium
formationoftheBex(OH)y)2(x(cid:2)y)þcomplexinsolutions chloride(BeCl2) andsodiumchloride (NaCl).
ofvariousmolefractionsofdioxanewereobtainedand Beryllium metal did not become readily available
shown to abideby the following reaction: until1957.Currently,themetalisproducedbyreducing
2Be2þþH O 0 Be OH3þþHþ BeF2 with Mg metal. The price on the US market for
2 2 vacuum-cast beryllium ingots was $338 per pound
Thus, it isclear that the Be2þcationin aqueous solu- ($745/kg)in 2001.
tionneverappearsbutisan“aquo-complex”.Thisillus- Themetal,beryllium,hashadmanyusesandapplica-
tratestheamphoteric natureofberyllium salts. tions in Industry.Among these arethe following:
Beryllium differs from its brothers (or sisters) in
Group 2 in that it usually forms covalent bonds. But, (cid:129) Becauseof its low atomic number andvery low
unlike other covalent molecules, it is soluble in organic absorption for X-rays, theoldestand still one of the
solventsand isa poorconductor whenmolten. mostimportant applications of beryllium isin
Because of its high affinity for oxygen at elevated radiationwindowsforX-raytubes.Extremedemands
temperatures and its ability to reduce water when its areplaced on purity andcleanliness of Be toavoid
oxide film is removed, the extraction of beryllium from artifacts inthe X-ray images. Thin beryllium foils are
its compounds is very difficult. Although electrolysis used as radiationwindows forX-ray detectors,and
of a fused mixture of beryllium and sodium fluorides the extremely low absorption minimizestheheating
was used to isolate the element in the nineteenth effectscausedby high intensity, low energyX-rays
century, the metal’s high melting point makes this typical of synchrotron radiation.
process more energy intensive than the corresponding (cid:129) Vacuum-tightwindowsandbeamtubesforradiation
productionofalkalimetalsbytheDown’sProcess.Early experiments on synchrotrons aremanufactured
inthetwentiethcentury,theproductionofberylliumby exclusively fromberyllium.In scientific setups for
the thermal decomposition of BeI was investigated variousX-ray emissionstudies,the sampleholder is
2
followingthesuccessofasimilarprocessfortheproduc- usuallymadeofberylliumbecauseitsemittedX-rays
tionofzirconium,butthisprovedtobeuneconomicfor have much lowerenergies (~100eV) than theX-rays
volume production. Beryllium metal is available frommost studiedmaterials.
commerciallyandisnevernormallymadeinthelabora- (cid:129) Becauseofitslowatomicnumber,berylliumisalmost
tory. Itsextraction from oresiscomplex. transparenttoenergeticparticles.Thereforeitisused
Themineralberyl,[Be Al (SiO ) ]isthemostimpor- to buildthe “beampipe” around the collision region
3 2 3 6
tantsourceofberyllium.Itisroastedwithsodiumhexa- in “Collider Particle Physics” experiments. Notably
fluorosilicate, Na SiF , at 700(cid:3)C to form beryllium all four main detectorexperiments at the Large
2 6
fluoride. This salt is water soluble and beryllium may HadronColliderAccelerator in Berne, Switzerland
beprecipitatedasthehydroxideBe(OH) byadjustment use a berylliumbeam pipe.
2
of thepH to 12. (cid:129) Beryllium’slowdensityallowscollisionproductsto
Pure beryllium may be obtained by electrolysis of reachthesurroundingdetectorswithoutasignificant
moltenBeCl containingsomeNaCl.Saltisaddedsince interaction.Itsstiffnessallowsapowerfulvacuumto
2
molten BeCl conducts very poorly. Another method beproducedwithinthepipetominimizeinteraction
2
involves the reduction of beryllium fluoride with withgases.Itsthermalstabilityallowsittofunction
magnesium at1300(cid:3)C: correctlyattemperaturesofonlyafewdegrees
abovetheabsolutezero,anditsdiamagneticnature
BeF þMg 0 MgF þBe
2 2 keepsitfrominterferingwiththecomplexmultipole