3. sc, lantanide

8/8/2019 3. Sc, lantanide

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Sc, Y, La subgroupCe family (lanthanides)

Th family (actinides)General propertiesElectronic configurationCompare the electronic config.of these elements (and their +3 ions)

with that of Al and of Ga subgroup (Ga,In,Tl)Conclusion : the elements of Ga subgroup have a similar atomic structure to Al in theground state but sharply different structures of their E3+ ions.

Element,Ion/ level

K L M N

Al 2 8 3

Ga 2 8 18 3

Sc 2 8 9 2

Al3+ 2 8 8

Ga3+ 2 8 18

Sc3+ 2 8 8

As a consequence:the properties of similar compounds in the series B,Al,Sc.Acchange uniformly, in contrast to the B,Al,Ga.Tl seriescompare for example : - atomic and ionic radii

-the heats of formation of the highest oxidesin the series B-La (p and d elements ) with that in B . Tl series (p elementsonly). What is observed? Explain

Element B Al Sc Y La Ac

Z 5 13 21 39 57 89

A 10.81 26.88 44.95 88.9 138.9 [227]

Valencyelectron

2s2

2p1

3s2

3p1

3d1

4s2

4d1

5s2

5d1

6s2

6d1

7s2

Atomicradius

0.91 1.43 1.64 1.81 1.87 2.03

Ionic radius,E3+

0.21 0.57 0.83 0.97 1.04 1.11

- H298(kJ/mol)E2O3

1461 1670 1715 1841 1902

B2O3 Al2O3 Ga2O3 In2O3 Tl2O3

- H298(kJ/mol)

1461 1670 1071 1004 502

Metallicproperties

Increases regularly in the series

Clark 10-3 10-3 10-3 10-9

Electrochemical characterSc and its analogues are far in front of hydrogenSc is slightly more metallic than Al, but resembles it in :

- reacts vigorously with H2O when the protective oxide layer is removed- hydrous oxide, Sc2O3.x H2O is amphoter

- only compounds in +3 oxidation state are formed- in its compounds, C.N greater 6 are unknown


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- there is no evidence for a lower O.S although are known phases with unusualstoichiometrie like:

- ScI2.17,ScBr2.3- Sc analogues are closer in their properties with alkaline earth metals (Ca)

Occurrence- are very dispersed, do not form separate minerals

Preparation : 1.- electrolysis of molten chlorides- 2.- metallothermic reduction :

- ScCl3 + Ca (10000C)Sc + CaCl2

- Ln2O3 + La (more 10000C) Ln + La2O3

Reactivity -increases down the group (like s group elements)

- with nonmetals at elevated temperatures- with diluted acids:

Sc, Y, La

M2O3, M2S3

MX3

MN

La(OH)3

X2

N2

ionic carbidesC

O2, S

H2O (t0C)

H2, B,

C, Si

MxEy

interstitialcompounds

acidsMX3

+H2

(HCl ,HNO3

, H2

SO4

)

+

wet airM(OH)3

the interstitial compounds are high melting compounds of metallic type with low-active nonmetals

What are high-temperature superconductors?At ordinary temperatures, metals have some resistance to the flow of electrons, dueto vibration of the atoms which scatter the electrons.As the temperature is lowered, the atoms vibrate less and the resistance decreases,until the materials critical temperature,TC is reached. At this temperature , theresistance drops abruptly to zero.;1911 Onnes,a Dutch physicist discovered that Hg loses all resistance to electrical

flow when cooled to about 4K, a current once started will flow continuously(superconductivity)1933 -Superconductors are also perfectly diamagnetic (repel a magnetic field)Meissner effectA magnetic field induces a current in a conductor;conversely, a current induces amagnetic fieldWhen a magnet approches a superconductor, it induces a current in thesuperconductor.Because there is no resistance to the current, it continues to flow,thus inducing its own magnetic field which then repels the magnets field.If themagnet is sufficiently small and strong, the repulsion will be enough tocounterbalance the pull of gravity and the magnet will levitate above the surface ofthe superconductor.Evolution of superconductivity:


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1987-Bednorz, Muller IBM Zurich (noble prize)92 K-first ceramic superconductor YBCO

(1:2:3-YBa2Cu3O7- )is an oxygen-deficient triple perovskite (ABO3)3A = central cations Y and Ba ; B= Cu cationstoday 125 K superconductor


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YBCO

YBCO is an oxygen-deficient triple perovskite, A3B3O9-x where Y and Ba are thecentral A cations and Cu the B cation. Oxygen is missing from the central Ylayer and from the a-axis of the basal plane.

Perovskite structure, ABX3The A atoms occupy the central positions and are coordinated to 12 X ionsB atoms are at the cell corners and are octahedrally coordinated.Typically B atoms are transition metalsand A atoms are large, electropositive atoms such as Ba, La

Cu(I) is coordinated to 4 oxygens in a square planar configuration,corner-sharing to form chains along the b-axis.

Cu(II) is square-pyramidally coordinated, with the CuO5 unitscorner-sharing to form buckled sheets in a-b plane.

The oxygen stoichiometry of YBCO can vary over the range 6


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Lanthanides, 4f2-14 5s25p65d0-16s2 La - [Xe]5d16s2

Element Z Electronicconfig

E0(V)Ln3+/Ln

Ionicradius

Ionizationpotential

Ce subfamily (Ce-Gd)

Cerium 58 4f 2 -2.48 1.034 36.2

Praseodymium 59 4f 3 -2.47 1.013 36.4

Neodymium 60 4f 4 -2.44 0.995 37.5Promerhium 61 4f 5 -2.42 0.979 38.4

Samarium 62 4f 6 -2.42 0.969 -

Europium 63 4f 7 -2.41 0.950 40.4

Gadolinium 64 4f 75d1 -2.40 0.938 41.8

Th subfamily (Tb-Lu)

Terbium 65 4f 9 (7+2) -2.38 0.923 38.8

Dysprosium 66 4f 10(7+3) -2.35 0.908 39.3

Holmium 67 4f 11(7+4) -2.32 0.894 40.4

Erbium 68 4f 12 -2.30 0.881 40.8

Thulium 69 4f

13

-2.28 0.869 40.5Ytterbium 70 4f 14 -2.27 0.858 41.8

Lutetium 71 4f 145d1 -2.25 0.848 40.4

Electronic configurationat lanthanides 4flevel have less energy than 5d, but the energetic difference is verysmall one (or two)4f electrons is easily excited, passes to 5d level, becomesvalence e-

Oxidation statesIn most compounds have O.S =+3 and not +2 (closeness of the properties to those ofSc subgroup elements)All lanthanides form M3+ ions (Gd and Lu only this O.S)

Certain lanthanides show M2+(Eu2+- 4f7 and Yb2+ - 4f14)M4+ (Ce4+ - 4f0 and Tb4+ - 4f7)

the special stability of other O.S. is associated with- an empty, half-filled or filled f shell- other thermodynamic and kinetic factorsO.S. the elements adjacent to La (4f0), Gd (4f7),Lu(4f14) have variable O.S

Ce(II),III,IV

PrIII,(IV)

Nd(II),III, (IV)

PmIII

SmIII,II

EuIII,II

GdIII, II

TbIII, (IV)

DyIII (IV)

HoIII

ErIII

TuIII (II)

YbIII,II

LuIII

Conclusion since the difference in structure if the atoms is exclusively in the N-shell(which does not greatly affect their chemical properties) all lanthanides are extremelyalike, a great similarity of properties

Some differences appear these are very important for separating lanthanides fromone another:

1. properties which uniformly change(lanthanide contraction)

- ionic radii a gradual, linear decrease

- redox potentials-


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Variation of ionic radii with Z-is theeffect of lanthanides contractiona low screening of one 4fe- by other4felectronswith Z increasing (and with theincreasing of number of 4f electrons),

each e-

suffers a suplimentary attractionfrom the nucleus

Variation of atomic radii with Za general decreasing like in the case of

ionic radiiexceptions:Eu and Yb probably intheir metallic lattices there are divalentions with greater volumesCe as tetravalent ion with smallervolume

Variation of redox potentials is another proof of the stability of different ionic speciesof lanthanides in water solutions

2. properties which periodically changeO.S.magnetic propertiesspectral (optic) properties

The colour of ions changes in accordance with greater or lower stabilization of the 4fstates4f0, 4f1, 4f7, 4f13 qnd 4f14 colouless

the rest are more or less intensely coloured is observed a repetition of colours ;ions with n electrons have the same colours as ions with ( 14-n ) electrons

Ion Number of unpaired e-

Colour Number of even e-

Ion

La3+(4f0) 0 colourless 0 Lu3=(4f14)

Ce3+(4f1) 1 colourless 1 Yb3+(4f13)

Pr3=(4f2) 2 green 2 Tu3+(4f12)

Nd3+(4f3) 3 reddish-violet 3 Er 3+(4f11)

Pm3+(4f4) 4 pink-yellow 4 Ho3+(4f10)

Sm3+(4f5) 5 yellow 5 Dy3+(4f9)

Eu3+

(4f6

) 6 pale yellow 6 Tb3+

(4f8

)Gd3+(4f7) 7 colourless

All the f states, except f0 and f14 contain unpaired electrons


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lanthanides are paramagnetic elementsat these elements magnetic effect arrising from the motion of the electron in itsorbital (orbital motion) contributes to the paramagnetism, as well as, that arising fromthe electrons spinning on its axis (spin motion)magnetic susceptibilities are calculated on the basis of spin and orbital contributions:(J = L + S orbital and spin

momemta)

KT

JJNg

M 3

)1(22

+

=

C.N. and stereochemistry lanthanide- In contrast to the delements, the felements may have C.N higher 9 (11, 12, 13,etc.)- lanthanide ions form (in comparation with dblock elementsfew complexes with ligands other than oxygen, and even those with nitrogen ligandsare often readily hydrolyzed

Occurrence and separation of lanthanidesLantahanides are always found in nature togetherClark is comparable to that of I2, Sb, Cu but lanthanides are very dispersedMore than 250 minerals containing lanthanides are knownMain ores for manufacturing are:

- phasphates monazite : (Ln,Th)PO4- fluorides; fluoride-carbonates; silicates

Separation of the individual lanthanide elements is one of the most difficult problemof inorganic chemistry. Explain.Steps :

- mineral concentration (by classical methods (magnetic or weight separations)- chemical tretment (acidic or basic decomposition)- separation of lanthanides as a group- separation of the individual lanthanide elements-The lanthanides properties which are used in eparation and the corresponding

separation methods

Property Separation method

Oxidation state Oxido-reduction procedure

Different solubility of some compunds Fractional crystallization (double salts)

Repartition coefficient Liquid-liquid extraction

Ionic change coefficient Ion exchangePressure of decomposition Thermal decomposition

Magnetic properties of ions Separation in magnetic field

Velocity of ions Electrophoresis

Constant of stability of complexcompounds

Combined procedures(crystallization,ion exchangeextraction


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Monazite (SiO2)(Ln,Th)PO4

+H2SO4 conc

insoluble in solutionresidue Th(SO4)2, Ln2(SO4)3

SiO2, TiO2 H3PO4 + (NH4)2C2O4

Ln2(C2O4)3 solutionTh(C2O4)2 C2O4

2-,PO43-

+(NH4)2C2O4in solution Ln2(C2O4)3 as a group

Th4+ t0C

Ln2O3

+H2SO4 + (NH4)2SO4

Ln2(SO4)3 . (NH4)2SO4Fractional

crystallization

Ion exchange - from citrate complexesCation exchange resin (Resin-H) :

3ResinH + Ln3+ (Resin)3Ln + 3H3O+

citricacid, buffered with ammonia to constant pH is added

Ln-(Resin)3 + 3 Hcit 3HResin + Lncit3

The heavier ions are smaller, they willbe more strongly complexed by thecytrate and the heavier lanthanideelements are washed down the columnfirst and will be eluted. If the conditionsare correct , the different elements willbe separated into pure components

Reactivity. Compounds-lanthanides (like La) come after the alkali and aline earth metals in chemical activity-are stable in dry air; at 200-4000C ignite in air and burn forming mixtures of oxidesand nitrides- form alloys with most metals and intermetallic compounds- react energetically with acids (but are stable in HF, H3PO4-are covered with insoluble salts films)do not dissolve in alkalis


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Compounds are practically ionic a direct consequence of relatively high sizes of Lnions in all O.SThe majority of lanthanides compounds (halides, nitrates, perchlorates,etc.) havehigh m.p.,

high solubility in polar solvents,electricalconductivity in solution

Oxides, Ln2O3- are basic oxides, refractory (m.p 20000C), practically insoluble in

water , react with it hydroxides

CeO2 obtained : Ce + O2CeO2Ce(C2O4)2 CeO2 + 2CO2 (decomp in O2)

Inert, insoluble in strong acids or alkalis

Hydroxides,Ln(OH)3 are amorphous precipitatesBasic character , thermal stability and solubility decrease from Ce(OH)3 to Lu(OH)3Oxosalts (double salts) are very common, used for the separation by fractionalcrystallization methodsComplex compoundsThe tendency of lanthanides to from complex compounds is determined by factors:- the 4f orbitals screening by the 5s25p6 octet infront of ligands interaction; so 4forbitals are not used to-from bonds and the bonds with (compounds can be regardedas containing Ln3+ ions surrounded by anions) ligands are especially ionic- each lanthanide ions in its O.S. (Ln3+, Ln2+, Ln4+) has relatively great size (incomparison with its electrical charge) so the strenght of bands (especially

electrostatic bands) is small- crystal field splitting of the 4f orbitals is minimalThe lanthanide elements are often six-coordinated in complexes, but highercoordinations (7, 8, 9, 10 and 12) are known.The C.N =8 is the most characteristic forheavier lanthanide ions.The tendency of lanthanides to have C.N. up to 12, is due to a combination of- their large size,- no directional requirements of the 4f orbitals (ionic bonding) and- minimal crystal field stabilization energy.

C.N Example Shapes


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8 La(acac)3(H2O)2

Y(CF3COOHCOOCF3)4-

antiprismatic form

dodecahedral form

9 [Nd(h2O)9](BrO3)3

10[La(H2O)4EDTA] 3 H2O

[M(NO3)5]2-(M = Ce, Y, Ln)

EDTA occupies sixposition

NO3-are present at the

apices of a trigonalbipyramid

12[Ce(NO3)6]

3-

La(C6H9N3)43+

almost regular

icosaedron

Uses of lanthanides- mischmetal (alloy of lanthanides with a predominant content of Ce and La)

-fabrication of special steels (pyroforic steels) the elements are notseparated ; the naturally occuring mix is converted to the chloride and thenreduced electrolytically to mischmetal

- mixed lanthanides addition to zeolites to increase catalytic activity, (inpetroleum crackers)

- Gd, Sm, Eu as control rods in atomic piles (neutron capture)- La2O3 glass industry- Lasers of high intensity (Nd oxide in yttrium aluminium garnet )- Ytrium in manufactory of warm superconductors

What are high-temperature superconductors?

At ordinary temperatures, metals have some resistance to the flow of electrons, dueto vibration of the atoms which scatter the electrons.As the temperature is lowered, the atoms vibrate less and the resistance decreases,until the materials critical temperature,TC is reached. At this temperature , theresistance drops abruptly to zero.;1911 Onnes,a Dutch physicist discovered that Hg loses all resistance to electricalflow when cooled to about 4K, a current once started will flow continuously(superconductivity)1933 -Superconductors are also perfectly diamagnetic (repel a magnetic field)Meissner effectA magnetic field induces a current in a conductor;conversely, a current induces a

magnetic fieldWhen a magnet approches a superconductor, it induces a current in thesuperconductor.Because there is no resistance to the current, it continues to flow,thus inducing its own magnetic field which then repels the magnets field.If themagnet is sufficiently small and strong, the repulsion will be enough tocounterbalance the pull of gravity and the magnet will levitate above the surface ofthe superconductor.Evolution of superconductivity:

1987-Bednorz, Muller IBM Zurich (noble prize)92 K-first ceramic superconductor YBCO

(1:2:3-YBa2Cu3O7- )is an oxygen-deficient triple perovskite (ABO3)3A = central cations Y and Ba ; B= Cu cations


11/11

today 125 K superconductor

YBCO

YBCO is an oxygen-deficient triple perovskite, A3B3O9-x where Y and Ba are the

central A cations and Cu the B cation. Oxyen is missing from the central Y layer andfrom the a-axis of the basal plane.

Cu(I) is coordinated to 4 oxygens in asquare planar configuration, corner-sharing to form chains along the b-axis.Cu(II) is square-pyramidally coordinated,with the CuO5 units corner-sharing toform buckled sheets in a-b plane.The oxygen stoichiometry of YBCO can

vary over the range 6

3. sc, lantanide

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