![39
• The stability of AnIV decreases along the series
Quite stable for Th, Pa, U, Np.
Only found in solution with fluoride for Am, Cm, Bk
The drop in E0 (An4+/An3+) at Bk reflects the stability
of [Rn]5f7 (BkIV).
• The trend in E0 (An3+/An2+) parallels the one in
E0 (An4+/An3+).
The stability of AnII increases across the series.
Note that the discontinuity appears at Cm, reflecting
the stability of [Rn]5f7 (CmIII).
• The greater range of oxidation numbers of An elements
compared with Ln is due to the nature of 5f orbitals](https://image.slidesharecdn.com/iim-201021095447/85/f-block-elements-39-320.jpg)
![41
Reduction potentials of 5f elements
E0 / V8
6
4
2
0
-2
-4
-6
An3+ / An2+
An4+ / An3+
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
[Rn]4f7](https://image.slidesharecdn.com/iim-201021095447/85/f-block-elements-41-320.jpg)
![49
Fuel reprocessing and treatment
1st stage: extraction of U and Pu
238 1 239 239 0 -
92 0 92 93 -1 1/2
239 0 -
93 -1 1
39
9 /2
2
4
U + n U Np + e ( ,t 24 min)
Np + e (Pu ,t 2 4 days).
b
b
238U produces 239Pu, which can also be used as fuel
TBP extraction
in kerosene (PUREX)
HNO3 7 M
nitrates
Other fission
products + An
[UO2(NO3)2(TBP)2]
[Pu(NO3)4(TBP)2
Np](https://image.slidesharecdn.com/iim-201021095447/85/f-block-elements-49-320.jpg)
![50
[UO2(NO3)2(TBP)2]
[Pu(NO3)4(TBP)2
FeII
PuIII(aq)[UO2(NO3)2(TBP)2]
UO3
UO2
H2
PUREX Plutonium-Uranium
Refining by EXtraction
HNO2
PuIV(aq)
oxalic acid
300 oC
PuO2](https://image.slidesharecdn.com/iim-201021095447/85/f-block-elements-50-320.jpg)
f block elements
- 1. 1 Dr.S.RADHA Assistant Professor of Chemistry Saiva Bhanu Kshatriya College Aruppukottai UNIT-5 f-BLOCK ELEMENTS Gd Gd Eu
- 2. 2 Pedagogical objective FF 4f4f 5f5f 1 21 2 3 4 5 6 7 83 4 5 6 7 8 SS PP DD 3d3d 4d4d 5d5d 6d6d 11 22 33 44 55 66 77 • Overview of f-elements properties, with reference to their uses in daily life and high technology applications • Mainly focused on 4f-elements Pre-requisites Coordination chemistry Quantum chemistry
- 3. 3 1.1 Definitions and discovery 1.2 Occurrence of 4f elements 1.3 Basic properties 1.3.1 Electronic configuration 1.3.2 Oxidation states of 4f elements 1.3.3 Oxidation states of 5f elements 1.4 Radioactivity of 5f elements Table of Contents Nuclear fuel rod assembly Particle filter for Diesel exhaust gases
- 4. 4 f-Block Elements 1.1 Definitions and discovery Lanthanides: 58-71 Ln Actinides: 90-103 An Parent elements La and Ac often included in Ln and An Rare earths: Sc, Y, La + Ce-Lu Discovery of rare earths 1794 (Y) – 1947 (Pm) Discovery of actinides 1789 (U) – 1971 (Lr) Naturally occurring: Ac, Th, Pa, U, (Np, Pu)
- 5. 5 1.1 The discovery of 4f-elements rare earths actinides Yttrium was discovered in 1794 by Johan Gadolin, in Åbo (Turku) 4f 5f lanthanides: Ce-Lu lanthanoids: La-Lu
- 6. 6 1787 Carl Axel Arrhenius, an artillery lieutenant and amateur geologist, finds a black mineral in a quarry near Ytterby, 30 km from Stockholm. 1788 B. R. Geijer (Stockholm) describes the mineral (d = 4.2) and names it ytterbite, presently known as gadolinite, with formula Be2FeY2SiO10. 1792 J. Gadolin (1760-1852) studies the mineral and publishes a 19-page report in 1794 in the Proceedings of the Royal Swedish Academy of Sciences, concluding to the presence of a new “earth”, which he names yttrium. Discovery of yttrium (1794) Subsequent work revealed that yttrium contained the oxides of 10 other elements.
- 7. 7 HNO3 / HCl SiO2Fe3+, Be2+, Y3+ K2CO3, pH = 4-5 O2, H2O Fe(OH)3 Y3+ NH3, pH = 7-8 Y(OH)3 Be2FeY2SiO10 Johan Gadolin, 1794 Chemical separation of yttrium Be(OH)2,FeCO3 taken as Al
- 8. 8 1751 The mineralogist Cronstedt finds a peculiar heavy stone near Batnäs. 1803 W. Hisinger and J. J. Berzelius analyse this stone and find it contains an unknown “earth” they name ceria after the recently discovered planet Ceres. Their finding is published in 1804 in a 24-page report and confirmed by the German chemist Klaproth. The silicate material has a variable composition close to (Ce,La)3MIIH3Si3O13 and is presently named cerite (M = Ca, Fe). Discovery of cerium (1804)
- 9. 9 Most of the other rare earths have been discovered by further analysing the two initial minerals, gadolinite and cerite. The main techniques were fractional precipitation and crystallisation, as well as flame spectroscopy (absorption and emission). These operations were tedious: for instance, 20 tons were needed to produce 82 mg of element 61 by ion-exchange separation techniques (61 = radioactive promethium), that is a fraction equal to 4x10-12 !) Other rare earths (1839-1947)
- 10. 10 1.2 Occurrence of 4f elements Abundance in cosmos relative to silicon: Si = 106 La-Lu The elements are “rare” but not rarer than many others, such as Au, Pt, Pd, Rh, for instance
- 11. 11 Natural abundance Abundance in earth’s crust expressed in ppm (g/ton) La Ce Nd Pr Sm Gd Eu Tb Dy Er Ho Tm Yb Lu Odd/even effect 56 58 60 62 64 66 68 70 72 0 10 20 30 40 50 0 10 20 30 40 50 Atomic number
- 12. 12 Cerium group (lighter elements) Bastnasite Ln(CO3)F 65-70% Monazite LnPO4 50-75% Cerite (Ce,La)3MIIH3Si3O13 50-70% Yttrium group (heavier elements) Xenotime LnPO4 55-65% Gadolinite Ln2M3Si2O10 35-50% Euxenite Ln(Nb,Ta)TiO6xH2O 15-35% Main resources (4f elements)
- 13. 13 Main resources World resources are estimated to 83 million metric tons for a present usage of about 40’000 metric tons a year China 50 % (?) Russia 25 % (?) USA 10 % Australia 5 % Other 10 % Baotou (Inner Mongolia)
- 14. 14 Applications of 4f-elements • Catalysts - cracking of hydrocarbons - conversion of exhaust gases (gasoline and diesel) • Metallurgy - Steel production (removal of O, S) - Nodular graphite - Hardener (e.g. in magnesium) • Materials - High temperature superconducting ceramics - Electronic devices (capacitors, O2-sensors) - Magnets (Sm5Co, Nd5Fe) - Neutron moderators in nuclear reactors - Hydrogen storage with metal hydrides
- 15. 15 CeO2 Gaz filtrés Gas produced by the engine Gas filtration Soot particles CeO2 EOLYS® Soot emission of Diesel engines reduced by 99.9 %
- 16. 16 • Optics and lighting - Polishing powders - Protection against sun (sunglasses) - Lasers, particularly Nd YAG - Phosphors for displays (incl. electrolumin. displays) - Fluorescent lamps • Medicine - Seasickness (Ce oxalate), thromboses (Nd oxalate) - Renal insufficiency (La2(CO3)3 .4H2O) - X-ray intensifying screens - NMR imaging - Cancer radio- and photo-therapy - Laser surgery (Nd YAG laser) - Luminescent immunoassays • Science - Shift reagents, luminescent and magnetic probes - Catalysts for organic chemistry
- 17. 17 fluorescent lamps Er amplifier for optical fibers rechargeable batteries
- 18. 18 pigments Re-inforced cast Al pistons MRI images
- 19. 19 1.3 Basic properties 1.3.1 Electronic configuration 4f-orbitals x(x2–3y2) y(3x2–y2) z(x2–y2)xyz xz2 yz2 z3
- 20. 20 4f-orbitals (in octahedral symmetry) xy z z3 y3 x3 xyz z(x2-y2) y(z2-x2) x(z2-y2) T2u T1u A2u
- 21. 21
- 22. 22
- 23. 23
- 24. 24
- 25. 25
- 26. 26 • Sc, Y and La introduce the 3d, 4d and 5d transition series: nd1(n+1)s2 n=3 (Sc), 4 (Y) and 5 (La) • The energy of the 4f orbitals decreases abruptly beyond La: -0.95 eV for La, -5 eV for Nd ! which leads to the filling of the 4f shell • The 4f orbitals lie outside the Xe electronic structure for La, but inside the Xe electronic structure for the other Ln elements Lanthanides Actinides • Similarly, the 5f orbitals are also “inner orbitals”
- 27. 27 inner nature of 4f (Nd3+) and 5f (U3+) orbitals
- 28. 28 Ln0 4fN-1 5d1 6s2 La, Ce, Gd, Lu 4fN 6s2 Pr-Eu,Tb-Yb 1.3.2 Oxidation states of 4f elements LnII 4fN-1 5d1 La, Gd 4fN Ce-Eu, Tb-Yb 4fN-1 6s1 Lu LnIII 4fN-1 (no exception)
- 29. 29 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 -2.2 -2.3 -2.4 -2.5 -2.6 -2.7 atomic number Volts Eo red : Ln3+(aq) + 3 e- D Ln(s) La Tb Lu • The more stable oxidation state of Ln is +3 Oxidation states of 4f elements Y (Z = 39) Sc (Z = 21, E o red = -2.08 V )
- 30. 30 Explanation: Upon ionization, all of the valence orbitals (4f, 5d, 6s) are stabilized, but to variable degrees. 4f orbitals are stabilized most and 6s least. After removal of three electrons, the remaining are very tightly bound Main reason: the fourth ionization energy is larger than the sum of the first three ones; this extra energy cannot, in most cases, be compensated by bond formation
- 31. 31 Ce Pr Pm Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 3400 3600 3800 4000 4200 4400 4600I/kJmol -1 I4 I1 + I2 + I3
- 32. 32 • Ce, Pr, Nd and Tb may have +4 oxidation state E 0 red for Ln4+(aq) + e- D Ln3+(aq) in acidic solutions: +1.72 V for Ce4+, stable in water +3.20 V for Pr4+, oxidizes water +3.10 V for Tb4+, oxidizes water • Sm, Eu, and Yb have a relatively stable +2 state E 0 red for Ln3+(aq) + e- D Ln2+(aq) in acidic solutions: -0.35 V for Eu2+, stable in water -1.15 V for Yb2+, reduces water -1.56 V for Sm2+, reduces water Oxidation states of 4f elements
- 33. 33 La Ce Pr NdSm Eu Gd Tb Dy Ho Er Tm Yb -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 E 0 red /V Ln3+ + e- D Ln2+ In water In thf Calculated -0.83
- 34. 34 Ce Pr Pm Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 1900 2000 2100 2200 2300 2400 2500 I3/kJmol -1 I3 LuII 4f145d1 YbII 4f14 GdII 4f75d1 EuII 4f7
- 35. 35 Ionic radii: lanthanide contraction 56 58 60 62 64 66 68 70 72 1.00 1.05 1.10 1.15 1.20 1.25 Ca II : 1.18 Å Sr II : 1.31 Å Ionic radii, CN = 9 0.18 Å Lu Gd La Z ri / Å
- 36. 36 Ionic radii: variation with coordination number CN 6 7 8 9 10 11 12 0.8 0.9 1.0 1.1 1.2 1.3 1.4 Ca II Eu III Yb III La III CN ri / Å
- 37. 37 56 58 60 62 64 66 68 70 72 1.70 1.75 1.80 1.85 1.90 1.95 2.00 2.05 2.10 La Ce Pr Nd PmSm Eu Gd Tb Dy Ho Er Tm Yb Lu atomic number Oxidation states in the 4f metals Atomic radii / Å for CN = 12 +3 +2
- 38. 38 1.3.3 Oxidation states of 5f elements An common other solid state only Th Pa U Np Pu AmCm Bk Cf Es Fm Md No Lr 2 3 4 5 6 7 Formaloxidationstate
- 39. 39 • The stability of AnIV decreases along the series Quite stable for Th, Pa, U, Np. Only found in solution with fluoride for Am, Cm, Bk The drop in E0 (An4+/An3+) at Bk reflects the stability of [Rn]5f7 (BkIV). • The trend in E0 (An3+/An2+) parallels the one in E0 (An4+/An3+). The stability of AnII increases across the series. Note that the discontinuity appears at Cm, reflecting the stability of [Rn]5f7 (CmIII). • The greater range of oxidation numbers of An elements compared with Ln is due to the nature of 5f orbitals
- 40. 40 Ac Th Pa U Np Pu AmCm Bk Cf Es FmMd No Lr 0 500 1000 1500 2000 2500 3000 3500 4000 4500I/kJmol -1 I4 I3 I2 I1
- 41. 41 Reduction potentials of 5f elements E0 / V8 6 4 2 0 -2 -4 -6 An3+ / An2+ An4+ / An3+ Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr [Rn]4f7
- 42. 42 Influence of relativity on f-orbitals 0 2 1 ( ) m m v c mass of a particle moving with velocity v For U(1s) : m = 1.35m0, leads to contraction of 1s On the contrary d and f orbitals are expanded and destabilized. 5f orbitals are more destabilized than 4f; they are more weakly bound and more chemically active, henceforth the larger range of oxidation numbers (and, also, larger covalency of the bonds) Effects are important for heavy elements
- 43. 43 Ionic radii: actinide contraction Th Pa U Np Pu Am Cm Bk Cf Es 65 70 75 80 85 90 95 100 105 110 115 An3+ An4+ An5+ r / pm
- 44. 44 1.4 Radioactivity of the actinides All of the An isotopes are radioactive, mostly a emitters. Z El. A t1/2 (* b-, EC) Z El. A t1/2 90 Th 232 1.401010 y 96 Cm 244 18.11 y 91 Pa 231 3.25104 y 97 Bk 247 1.38103 y 92 U 235 7.04108 y 98 Cf 249 351 y 238 4.47109 y 99 Es 252 472 d 93 Np 236 1.55105 y* 100 Fm 257 100.5 d 94 Pu 239 2.41104 y 101 Md 258 56 d 244 8.26107 y 102 No 259 1 h (a + EC) 95 Am 241 4.32102 y 103 Lr 262 3.6 h
- 45. 45 Nuclear fission 235 92U 1 0n 91 36Kr 142 36Ba A large nucleus is split into two smaller (and more stable) ones by collision with a thermal neutron. The process releases several neutrons, which in turn collide with other nuclei, initiating “chain reaction”, provided a “critical mass” exists, i.e. a minimum amount of the fissile product. thermal neutron ca. 2 kJmol-1
- 46. 46 The nucleus mass is smaller than the sum of the masses of its constituting particles (neutrons, protons), due to the nuclear forces. Henceforth the concept of “cohesion energy”, usually given per nucleon: 1 MeV = 1.6´10-13 J Kr Ba fission fusion
- 47. 47 Nuclear power generation Control rods Fuel rods Best natural isotope: 235U Natural abundance: 0.72 %, henceforth the need for enrichment. Fuel: UO2 enriched to 2-3% 235U, under the form of pellets stuffed into Zr tubes Cooling fluid (H2O, D2O) Steam Control rods: boron nitride or graphite (absorb neutrons) The cooling fluid also acts as moderator, slowing down the produced neutrons (boric acid added).
- 48. 48 • Gaseous diffusion of UF6 through Al or Ni membranes (pore size 10-25 nm). Graham’s law: 3000 passes needed (large and expensive fluorine- resistant chemical plants) for 90% enrichment Isotope separation 1 MW diffv • Centrifugation of UF6 (238UF6 concentrates near the walls) • Laser separation (now abandoned) Ionization energy of 235U slightly different from 238U Laser with wavelength tuned for ionizing 235U produces 235U+ which is collected on an electrode 235 6 238 6 ( UF ) 352 1 0043 ( UF ) 349 diff diff v . v a
- 49. 49 Fuel reprocessing and treatment 1st stage: extraction of U and Pu 238 1 239 239 0 - 92 0 92 93 -1 1/2 239 0 - 93 -1 1 39 9 /2 2 4 U + n U Np + e ( ,t 24 min) Np + e (Pu ,t 2 4 days). b b 238U produces 239Pu, which can also be used as fuel TBP extraction in kerosene (PUREX) HNO3 7 M nitrates Other fission products + An [UO2(NO3)2(TBP)2] [Pu(NO3)4(TBP)2 Np
- 50. 50 [UO2(NO3)2(TBP)2] [Pu(NO3)4(TBP)2 FeII PuIII(aq)[UO2(NO3)2(TBP)2] UO3 UO2 H2 PUREX Plutonium-Uranium Refining by EXtraction HNO2 PuIV(aq) oxalic acid 300 oC PuO2
- 51. 51 2nd stage: separation of radioactive wastes 1000 kg irradiated fuel 957 kg U 10 kg Pu 0.8 kg minor actinides 33 kg fission products Np, Am, Cm Zr 3.6 kg Cs 2.7 kg Tc 0.8 kg Sm 0.8 kg Se, Sn, I 0.3 kg Radioactive Xe, 3H2 Other non radioactive 24.8 kg of which 2 kg radioactive320 g 420 g 30 g
- 52. 52 Other fission products DIAMEX Am, Cm, Ln AmIII, CmIII LnIII(aq) Glass SANEX Selective Actinide EXtraction Am Cm N N N N NN