• General characteristics of Inner-transition Elements: f-block Elements (Actinides)

• The elements in which the last electrons enters one of the 5-f orbitals are called 5f-block elements or second inner transition series .These are also called actindes or actinons or actinoids because they come immediately after actinium(Ac).

• The 14 elements with atomic number 90-103 (Thorium toLawrencium) constitute the series of elements known as actinides.

• Dr.Anil Kumar Soni• (Assistant Professor)• Departmentof Chemistry,• Shia P.G.College,Lko.

• Source Of Actinides:• Uranium(U) and Thorium)Th) alone occur nature in the form

of ores and traces of actinium.Protactinium(Pr),Neptunium(Np), Plutonium(Pu) have beenisolated from uranium ores. All the actinides elements areproduced synthetically.

• Physico-Chemical properties of 5f-block (actnide) elements

• Electronic Configuration- G.E.C.[Rn]865f1-146d0-17s2

Actinium (Ac89 ) [Rn]86 5f0 6d1 7 s2 6d1 7 s2

(2,8,18,32,19,9,2)

Thorium, (Th90 ) [Rn]86 5f0 6d2 7 s2 6d2 7 s2

(2,8,18,32,18,10,2)

Protactinium, (Pa91 ) [Rn]86 5f2 6d2 7 s2 5f2 6d1 7 s2

(2,8,18,32,20,9,2)

Uranium, (U92 ) [Rn]86 5f3 6d2 7 s2 5f3 6d1 7 s2

(2,8,18,32,21,9,2)

Neptunium, (Np93 ) [Rn]86 5f4 6d1 7 s2 5f4 6d1 7 s2

(2,8,18,32,22,9,2)

Plutonium (Pu94 ) [Rn]86 5f6 6d0 7 s2 5f6 7 s2

(2,8,18,32,24,8,2)

Americium (Am95 ) [Rn]86 5f7 6d07 s2 5f7 7 s2

(2,8,18,32,25,8,2)

Curium ( Cm96 ) [Rn]86 5f7 6d17 s2 5f7 6d1 7 s2

(2,8,18,32,25,9,2)

Berkelium (Bk97) [Rn]86 5f9 6d07 s2 5f97 s2

(2,8,18,32,27,8,2)

Califormium (Cf97) [Rn]86 5f10 6d07s2 5f107 s2

(2,8,18,32,28,8,2)

Einsteinium, (Es99 ) [Rn]86 5f11 6d0 7 s2 5f11 7 s2

(2,8,18,32,29,8,2)

Fermium (Fm100 ) [Rn]86 5f12 6d0 7 s2 5f12 7 s2

(2,8,18,32,30,8,2)

Mendelevium (Fm101 ) [Rn]86 5f13 6d0 7 s2 5f13 7 s2

(2,8,18,32,31,8,2)

Nobelium (Fm102 ) [Rn]86 5f14 6d0 7 s2 5f14 7 s2

(2,8,18,32,32,8,2)

Lawrencium (Lw103) [Rn]86 5f14 6d1 7 s2 5f14 6d17 s2

(2,8,18,32,32,9,2)

Oxidation State:

The actinide elements exhibit variable valencies similar

to the transition metals.The oxidation state vary from +2 to +7. however post

Americium actinides are similar to lanthanides, in that +3 oxidation state is the

most stable and common one.

Actinides Oxidation statesAc89 +2, +3, +4

Th90 +2, (+3), +4 , +5

Pa91 (+3), +4, +5

U92 +3, +4, +5, +6

Np93 +3, +4, +5,+6,+7

Pu94 +3, +4, +5,+6,+7

Am95 +2,+3,+4,+5,+6

Cm96 +3,+4

Bk97 +3

Cf98 +3

Es99 +3

Fm99 +3

Md101 +3

No102 +3

Lw102 +3

The actinides shows actinide contraction (very much like lanthanide contraction) due to poor

Actinide Contraction (atomic and ionic radii M3+

ion)-The actinides

shows actinide contraction (very much like lanthanide contraction) due to poor shielding effect of 5f-electrons. As a result, the radii of the atoms or ions of these metals decrease regularly across the period. The contraction is greater from element to element in this series due to poorer shielding by 5f-electron. This is because 5f orbitals extend in space beyond 6s and 6p orbitals whereas 4f orbitals are inter deep inside the atom.

Colour-

Most of the tripositive and tetra positive actinide cation (M3+

and M4+cations) are coloured.

• The colour show that M3+ and M4+ cation having 5f0 (no 5f

subshell),5f7 (hal-filled 5f-orbital)and 5f14 (full filled 5f-

orbital)are colourless. While those containing 5f2 , 5f3 ,5f4 and

5f5,5f6 configuration are coloured.In other words we can say

that the cation having n=0,7, or 14 are colour less and the

cations containing n=2,3,4,5 or 6 are coloured.The colours

arise out due to electronic transition between various states

within the 5f subshell (f-f transition).

Magnetic Behaviour-Like lanthanoids the actinoid elements are

strongly paramagnetic.The magnetic properties of the actinide are quite

complex.The effects of ligand field on the compounds of actinide elements is

much more than the lanthanide elements.The 5f electron of the actinides

interact much more with the ligands than do the 4f electrons of lanthenides.

The spin orbit coupling and the ligand field effects both contribute appreciably

to the magnetic properties of the actinide and thus none of the two formoula

discussed earlier i.e 𝝁eff = ⎷n(n+2)(spin only formoula) and μ = g⎷J(J+1)

(spin-orbit coupling involved) is adequate for the calculation of magnetic

moment of actinides.

Transuranic Elements

A number of elements beyond Uranium i.e. 92U238 have been prepared in

the laboratory by nuclear reactions. These elements are known as

transuranic elements.

Preparation of Transuranic Elements

It was found by Seaborg at the university of california that

when 92U238 is bombarded with 0n

1give rise to an element of a

higher mass number

• 92U238 + 0n

1 ⇨ 92U239 + γ rays

• This is new isotope of U is much more radiactive than the natural uranium. It emits a beta particle and gives a new element of atomic 93 which does not occur in nature.This element is named neptunium.

•

• 92U239 ⇨ 93Np239 + -1e

0 (β-particle)•

• (Np was discover by Mcmillan and Abelson in 1940) .

•

• Plutonium (Pu94)- It was discoverd by Seaberg,Mcmillan, Kennedy and

Wahi in 1941.

• 92U239 ⇨ 94Pu239 + -1e

0 (β-particle)

• 92U238 + 1H

2 ⇨ 93Np239 + 0n1 ⇨ 94Pu239 +-1e

0 (β-particle)•

•

• Americium (Am95)- It was discovered by

Seaberg,James, Morgan and Ghiorsoin 1945.

• 92U238 + 2He4 ⇨ 94Pu241 + 0n

1 ⇨ 95Am241 +-1e0(β-particle)

• Curium (Cm95)-• It was discovered by seaborg,James and

Ghiorso in 1949 prepared by bombarding helium particle on

uranium-239.

• 92U239 + 2He4 ⇨ 96 Cm 242 + 0n

1 (neutron)

• Berkelium (Bk97)- It was discovered by Thomson,Ghiorso, Seaborg in

1950. It was prepared by helium bombarded on Am-241.

• 95Am241 + 2He4 ⇨ 95Bk241 + 2 0n1

• Californium (Cr98)- It was discovered by Thomson, Ghiorso Seaborg and

Street in 1950 and prepared by helium ions bombarded on Cm-242.

• 96 Cm242 + 2He4 ⇨ 98 Cf 242 + 5 0n1

•

Einsteinium- It was discovered by ghiorso and co-workers in 1952

and prepared by irradiation of U-238 with N-14.

92U238 + 7N

14 ⇨ 99 Es247 + 5 0n1

Fermium – It was discovered by ghiorso and co-workers in 1953 and

prepared by bombarding Es-254 with neutrons.

99 Es254 + 0n1 ⇨ 99 Es255 + γ (gama )

⨽ 100Fm255 + -1e0

• Mendelevium- It was discovered by Ghioso and coworkers in 1955

and prepared by bombardment of Es-253 with helium .

99Es253 + 2 He4 ⇨ 101Md256 + 0n1

Nobelium - It was discovered by Ghioso and coworkers in 1958 and

prepared by bombardment of Cm-246 with carbon atom.

96Cm246 + 6C12 ⇨ 102No254 + 4 0n

1

• Lawrencium- It was discovered by Ghioso and coworkers in 1961 and

prepared by bombardment of Cf-245 with Boran atom.

• 98 Cf245 + 5B10 ⇨ 103Lw254 + 0n

1

• Seperation of Actinide Elements• Transuranic elements produced as a result of nuclear reactions are isolated

by followind methods.

• Precipitation Methods- Only M3+ and M4+ can be precipitated as fluorides

or phosphates from solution of HF or H3PO4. There is no precipitation in

higher oxidation states or precipitation can be prevented by complexation

with addition of sulphate or other ions. This method is particularly useful

for the separation of U, Np, Pu and Am. When the quantity of the actinide

ion is insufficient to precipitate by itself,co-precipitation with a carrier like

LaF3 (used for the seperation of Np and Pu from U and fission products) or

• BiPo4 (used for the seperation of Pu from U and fission products ) is

adopted.

2- Solvent extraction method- This method is based on the

distribution of a metal between the aq. Solution and an organic solvent. Thus with methyl isobutyl ketone (hexone) Np4+ , Np5+ ,Pu 6+ and U6+ are extracted while Pu 3+ is not extracted. The actinide ions are extracted from nitrate solution in to ethers. The actinide +4 ions are extracted in to tributyl phosphate (TBP) in kerosene from 6M Nitric acid. The actinides +3 ions are similarly extracted from 10-16 M HNO3 .

3- Ion exchange method- This is the best method for the seperation of the trans uranic element(post americium elements) and also for tracer quantities of Np ,Pu and Am. This method invoves the following two types.

(a)- Lanthanide –Actinide Seperation- The actnide as a group may be seperated from lanthanides by using Conc. HCl or 10 M LiCl. This is because the actinide ion more readily from chloro complex anions than lanthanides, Hence actinides can be removed from cation exchange resin or conversely adsorbed on anion exchange resin.

(b)- Seperation of individual actinide elements- The actinide ions,in general can be seperated from each other by removing from the cation exchange resin by elution with ammonium citrate, lactate, α-hydroxy isobutyrate and EDTA. Lw(103) leaves the calumn first followed by No(102) and so on down the scale of atomic numbers.

Comparison of 4f and 5f-block elements-

➢ In both the series the last electron goes to f-orbital.

➢ Both lanthanide and actinides show variable oxidation state but the common oxidation state for the both series is +3.

➢ The elements of both the series are paramagnetic in nature.

➢ Both show adsorption spectra bands due to f-f transition.

➢ Both have a tendency to form complex compounds.

➢ In both the series there is a contraction in size as the atomic increase, called Lanthanide and Actinide contraction.

➢Dissimilarties between 4f and 5f-block

elements-➢ In lanthanide electrons enter to the 4f-orbital while in actinide enter 5f-orbital

➢ In lanthanide the highest oxidation state is +4 while in actinides +6 and +7.

➢ Binding energies of 4f-orbital are higher than 5f-orbital.

➢ 4f-electrons have greater screening effect. While 5f-electrons have poor

screening effect.➢ All lanthanides are non radio active except Pr (promethium). While all actinides are

radio active.

➢ Lanthanides have less tendency to form complex while actinides have greater

tendency to form complex.