f-block-element.ppt

Chemistry

2. SESSIONOBJECTIVES
1.f-Block elements
2.Introduction to lanthanides
3.Oxidation state
4.lanthanide contraction
5.Chemical reactivity
6.Introduction of Actinides
7.Comparison of actinides with lanthanides

3. INNERTRANSITIONELEMENTS
Theelementsinwhichtheadditionalelectron
enters(n-2)forbitalsarecalledinnertransition
elements.Thevalenceshellelectronicconfiguration
oftheseelementscanberepresentedas(n–2)f
0-
14
(n–1)d
0-1
ns
2
.
4finnertransitionmetalsareknownaslanthanides
becausetheycomeimmediatelyafterlanthanum
and5finnertransitionmetalsareknownas
actinoidsbecausetheycomeimmediatelyafter
actinium.

4. ELECTRONICCONFIGURATION
Element name Symbol Z Ln Ln
3+
Radius
Ln
3+
/ pm
Lanthanum La 57 [Xe]6s
2
5d
1
[Xe]4f
0
116
Cerium Ce 58 [Xe]4f
1
6s
2
5d
1
[Xe]4f
1
114
Praesodymium Pr 59 [Xe]4f
3
6s
2
[Xe]4f
2
113
Neodymium Nd 60 [Xe]4f
4
6s
2
[Xe]4f
3
111
Promethium Pm 61 [Xe]4f
5
6s
2
[Xe]4f
4
109
Samarium Sm 62 [Xe]4f
6
6s
2
[Xe]4f
5
108
Europium Eu 63 [Xe]4f
7
6s
2
[Xe]4f
6
107
Gadolinium Eu 64 [Xe]4f
7
6s
2
5d
1
[Xe]4f
7
105
Terbium Tb 65 [Xe] 4f
9
6s
2
[Xe]4f
8
104
Dysprosium Dy 66 [Xe] 4f
10
6s
2
[Xe]4f
9
103
Holmium Ho 67 [Xe] 4f
11
6s
2
[Xe]4f
10
102
Erbium Er 68 [Xe] 4f
12
6s
2
[Xe]4f
11
100
Thulium Tm 69 [Xe] 4f
13
6s
2
[Xe]4f
12
99
Ytterbium Yb 70 [Xe] 4f
14
6s
2
[Xe]4f
13
99
Lutetium Lu 71 [Xe] 4f
14
6s
2
5d
1
[Xe]4f
14
98

5. ATOMICANDIONICSIZES: THE
LANTHANIDECONTRACTION
Astheatomicnumber increases,each
succeedingelementcontainsonemoreelectron
inthe4forbitalandoneprotoninthenucleus.
The4felectronsareineffectiveinscreeningthe
outerelectronsfromthenucleuscausing
imperfectshielding.Asaresult,thereisa
gradualincreaseinthenucleusattractionforthe
outerelectrons.Consequentlygradualdecrease
insizeoccur.Thisiscalledlanthanidecontraction.

6. ILLUSTRATIVEEXAMPLE
Explainthecauseandtwoconsequences oflanthanoid
contraction.
Solution:
The poor shielding effect of f-electrons is cause of lanthanoid
contraction.
Consequences
Thereiscloseresemblancebetween4dand5dtransition
series.Ionizationenergyof5dtransitionseriesishigherthan
3dand4dtransitionseries.Difficultyinseparationof
lanthanides

7. ILLUSTRATIVEEXAMPLE
Why Zr and Hf have almost similar atomic radii?
Solution
ZrandHfhavealmostsimilaratomicradiiasa
consequenceoflanthanidecontractionduetowhich
theirpropertiesbecomessimilar.

8. ILLUSTRATIVEEXAMPLE
Size of trivalent lanthanoid cation decreases with increase in
atomic number. Explain.
Solution
Itisduetopoorshieldingeffectoff-electrons,
valanceelectronsarestronglyattractedtowards
nucleus,therefore,effectivenuclearcharge
increases,henceionicsizedecreases.

9. IONIZATIONENTHALPIES
Firstionizationenthalpyisaround600kJmol
-1
,the
secondabout1200kJmol
-1
comparable withthoseof
calcium.
Colours of these ions may be attributed to the presence
of f electrons. Neither La
3+
nor Lu
3+
ion shows any colour
but the rest do so.
Absorptionbandsarenarrow,probablybecauseofthe
excitationwithinflevel.
Colours:

10. MAGNETICPROPERTIES
Lanthanideshaveveryhighmagneticsusceptibilitiesdueto
theirlargenumbersofunpairedf-electrons.
Thelanthanoidionsotherthenthef
0
type(La
3+
andCe
3+
)
andthef
14
type(Yb
2+
andLu
3+
)areallparamagnetic.The
paramagnetism risestothemaximum inneodymium .
Thestrongest known magnets contain
lanthanides(eg.Nd-Fe-B,Sm-Fe-N,andSm-
Co).
Lanthanide complexes are
used inMRI(medical
resonance imaging), eg.
[Gd(III)(dtpa)]
2-

11. OXIDATIONSTATES
Predominantly +3 oxidation state.
Occasionally+2and+4ionsinsolutionorinsolid
compounds arealsoobtained.
This irregularity
arises mainly
from the extra
stability of empty,
half filled or filled
f subshell.

12. ILLUSTRATIVEEXAMPLE
WhySm
2+
,Eu
2+
,andYb
2+
ionsinsolutionsaregoodreducing
agentsbutanaqueoussolutionofCe
4+
isagoodoxidizing
agent?
Solution
Themoststableoxidationstateoflanthanidesis
+3.Hencetheionsin+2oxidationstatetendto
change+3statebylossofelectronactingas
reducingagentswhereasthosein+4oxidation
statetendtochangeto+3oxidationstatebygain
ofelectronactingasagoodoxidisingagentin
aqueoussolution.

13. LUMINESCENCE OFLANTHANOIDCOMPLEXES
IrradiationofsomeLanthanide(III) complexes withUVlight
causesthemtofluoresce
Theoriginoffluorescenceis4f-4ftransitions.
–theexcitedstateproduceddecaystothegroundstatewith
emissionofenergy.
SomeexamplesareEu
3+
(red)andTb
3+
(green)
Theycanbeusedasphosphors intelevisionsetsand
fluorescentlighting.
Theseapplicationsarespecifictolanthanoidionsbecauseofthe
sharptransitionsobserved.

14. PROPERTIES
Silverywhitesoftmetals,tarnishin
airrapidly
Hardness increaseswithincreasing
atomicnumber,samarium beingsteel
hard.
Good conductor of heat and electricity.

15. CHEMICALPROPERTIES
Metalcombineswithhydrogenwhengentlyheated
inthegas.
Thecarbides,Ln
3C,Ln
2C
3andLnC
2areformed
whenthemetalsareheatedwithcarbon.
Theyliberatehydrogenfromdiluteacidsandburn
inhalogenstoformhalides.
Theyformoxidesandhydroxides,M
2O
3and
M(OH)
3,basiclikealkalineearthmetaloxidesand
hydroxides.

16. Ln
W
ith
a
c id
s
With helogensHeated with S
H
eated w
ith
N
2
B
u
r
n

w
i
t
h

O
2
2
C 2773 K
W
i
t
h

H

O
Ln S
23
2
3
2
2LnN
LnC
Ln(OH) +H
3LnX
H
Ln O
23

17. USES
Best single use of the lanthanoids is for the
production of alloy steels for plates and pipes.
Awellknownalloyismischmetalwhichconsistsof
alanthanoidmetal(~95%)andiron(~5%)and
tracesofS,C,CaandAl.Agooddealofmisch
metalisusedinMgbasedalloytoproducebullets,
shellandlighterflint.
Mixed oxides of lanthanoids are employed as
catalysts in petroleum cracking.

18. THEACTINIDES
Result from the filling of the 5f orbitals.
The others must be made by nuclear processes.
Only Th and U occur naturally-both are more
abundant in the earth’s crust than tin.
All isotopes are radioactive, with only
232
Th,
235
U,
238
U and
244
Pu having long half-lives.

19. SOMECHARACTERISTIC PROPERTIESOFACTINIDES
The dominant oxidation state of actinides is +3.
Actinides also exhibit an oxidation state of +4.
Some actinides such as uranium, neptunium and
plutonium also exhibit an oxidation state of +6.
The actinides show actinide contraction (like
lanthanide contraction) due to poor shielding of
the nuclear charge by 5f electrons.
All the actinides are radioactive. Actinides are
radioactive in nature. So the study of their
chemistry is difficult in the laboratory. Their
chemistry is studied using tracer techniques.

20. ELECTRONICCONFIGURATION
Element name Symbol Z Ln Ln
3+
Radius
Ln
3+
/ pm
Actinium Ac 89 [Rn] 6d
1
7s
2
[Rn]4f
0
111
Thorium Th 90 [Rn ]5d
2
7s
2
[Rn]4f
1
Protactinium Pa 91 [Rn]5f
2
6d
1
7s
2
[Rn]4f
2
Uranium U 92 [Rn]5f
3
6d
1
7s
2
[Rn]4f
3
103
Neptunium Np 93 [Rn]5f
4
6d
1
7s
2
[Rn]4f
4
101
Plutonium Pu 94 [Rn]5f
6
7s
2
[Rn]4f
5
100
Americium Am 95 [Rn]5f
7
7s
2
[Rn]4f
6
99
Curium Cm 96 [Rn]5f
7
6d
1
7s
2
[Rn]4f
7
99
Berkelium Bk 97 [Rn]5f
9
7s
2
[Rn]4f
8
98
Californium Cf 98 [Rn]5f
10
7s
2
[Rn]4f
9
98
Einsteinium Es 99 [Rn]5f
11
7s
2
[Rn]4f
10
Fermium Fm 100 [Rn]5f
12
7s
2
[Rn]4f
11
Mendelevium Md 101 [Rn]5f
13
7s
2
[Rn]4f
12
Nobelium No 102 [Rn]5f
14
7s
2
[Rn]4f
13
Lawrencium Lr 103 [Rn]5f
14
6d
1
7s
2
[Rn]4f
14

21. IONICSIZES
Magnetic properties are more complex than those of
lanthanoids.
Susceptibility is roughly parallel to the lanthanoids.
Actinidecontractionoftrivalentionsissimilar
tothatofthelanthanides,andiscausedagain
bytheincreasingnuclearcharge.
Magnetic properties

22. PHYSICALANDCHEMICALREACTIVITY
Silveryinappearancebutdisplayavarietyofstructuresdue
totheirregularityinmetallicradiiwhicharefargreaterthan
arefoundinlanthanoids.
Highly reactive metals, especially when finely divided.
Action of boiling water gives mixture of oxides and hydroxides.
Combination withmost non-metals takesplaceat
moderatetemperature.
HCl attacks all metals but most are slightly affected by
HNO
3owing to the formation of protective oxide layers.
Alkalies have no effect.

23. COMPARISONOFLANTHANIDESANDACTINIDES
Similarities
Lanthanidesandactinidesinvolvefillingoff-orbitalsand
thusaresimilarinmanyrespects.
Themostcommon oxidationstateis+3forboth
lanthanidesandactinides.
Bothareelectropositiveinnatureandthusveryreactive.
Magneticandspectralpropertiesareexhibitedbyboth
lanthanidesandactinides.
Actinides exhibit actinide contraction just like lanthanides.

24. DIFFERENCES
Besides+3,lanthanidesalsoshowoxidationstatesof+2
and+4whileactinidesshowhigheroxidationstatesof
+4,+5,+6and+7aswell.
Lanthanideionsarecolourlesswhilemostoftheactinide
ionsarecoloured.
Actinideshaveagreatertendencytowardscomplex
formationascomparedtolanthanides.

25. Lanthanide compounds are less basic while actinide
compounds have appreciable basicity
ActinidesformfewimportantoxocationssuchasUO
2
2+
,
PuO
2
2+
,etc,whilesuchoxocationsarenotknownfor
lanthanides.
Almostallactinidesareradioactivewhilelanthanides,
exceptpromethium, arenon-radioactive.
Themagnetic propertiesofactinidescanbeeasily
explainedwhileitisdifficulttodosointhecaseof
lanthanides.

26. ILLUSTRATIVEEXAMPLE
Whydolanthanoidsandactinoidshavesamephysicaland
chemicalproperties?
Theyhavesimilarelectronicconfigurationandf-orbital
isprogressivelyfilled.
Solution

27. Thank you