f block element

F – BLOCK ELEMENT

(n-2)f

Introduction

• Penultimate (n -1)d • prepenultimate (n -2)f• Inner transition element- e- use is both shell.• Intermediate behavior like d- block element.• 2 series of f- block element-• Lanthanide series – our main topic.• actinide series- radioactive.

Lanthanide series

• La(57) Ce(58) Pr(59)• Nd(60) Pm(61)

Sm(62)• Eu(63) Gd(64) Tb(65)• Dy(66) Ho(67) Er(68)• Tm(69) Yb(70) Lu(71)• 14 element is called lanthanide series.• General electronic configuration 4f1-14 5d0-1 6s2

Ln Greek hidden

Lanthanum, a “rare earth” is used in camera lenses amongst other things. Lanthanum is found in uranium minerals

Cerium

Sparking light. Also used in permanent magnet.

Praseodymium

Neodymium

Neodymium- strong magnet

Neodymium

Europeium

• Europium is used to produce blue, red and white radiances in computer monitors and television screens. It is also used in energy efficient light bulbs.

Position of lanthanoids

13

67

57 -7189-103

Total= 14 elementSame no. of valency 5d1 and 6s2.

Same chemical & physical property.Fill orbital 4f5f

Electronic configuration of lanthanoids

• E.C Based on aufbau principle .La (57) 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 5d1 6s2

[Xe] – 541s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 The electronic configuration of Ln is[Xe] 4f0 5d1 6s2 or [Xe] 4f0

Similarly Ce- 4f1, Pr- 4f2,……… Lu-4f14.(expected)but observed E.C is not true for all element.

Electronic configuration of lanthanoids

Oxidation state

• Common oxidation state is +3 more stable.• Loses of two 6s electron and one 5d or 4f

electron.• Some either show +2 or +4 Oxidation state.• Ln [Xe] 4f0 5d1 6s2 and Ln+3 [Xe]4f0 5d0 6s0

Ln, Pm, Ho, Eb, Lu +3Ce, Pr, Tb, Dy +3, +4Sm, Eu, Tm, Yb +2, +3Nd, +2, +3, +3

Chemical reactivity of Lanthanids

1. Carbides-C2. Hydrides- H2

3. Oxides- O2

4. Reaction with nitrogen5. Reaction with mineral acids6. Reaction with water7. Reaction with sulphure

• The first few members of the lanthanoids are quite reactive and show chemical behaviour similar to that of calcium. The standard electrode potentials of the Ln+3/Ln couple indicate that all the lanthanides are more reactive than aluminium.

• These metals combine with hydrogen when heated gently in the gas, and form hydrides of the type LnH2 and LnH3.


• lanthanoids (Ln)Ln + 3H2 → 2LnH3

lanthanoid Hydrogen Lanthanoid hydride

2Ln + 3O2 → 2Ln2O3

lanthanoid Oxygen Lanthanoid Oxide• The oxide Ln2O3 react with water to form insoluble hydroxides.

Ln2O3 + 3H2O → 2Ln(OH)3

Ln2O3 + 3CO2 → Ln2(CO3)3


• On being heated, these elements combine directly with non-metals, and form carbides with carbon, nitrides with nitrogen, sulphides with sulphur, and halides with halogens.

• 2773KLn + 2C → 2LnC2

lanthanoid carbon Carbide• Δ

2Ln + N2 → 2LnNlanthanoid Nitrogen Nitride Δ2Ln + 3S → 2Ln2S3

lanthanoid Sulphur Sulphide


• 2Ln + 3H2O → 2Ln(OH)3 + 3H2

lanthanoid water Halide

• They liberate hydrogen from dilute acids. Δ 2Ln + 6HX → 2LnX3 + 3H2↑lanthanoid Nitrogen Halide hydrogen


Lanthanoid contraction and its consequences

Lanthanoid contraction

• The gradual decrease in atomic and ionic size of lanthanoides with increase in atomic number is called lanthanoide contraction.

• Causes of Lanthanoid contraction-• As atomic no. increase the positive charge also

increase.• As atomic no. increase other thing decreases• Atomic radius= ionic radius > screen effect.

Effects of Lanthanoid contraction

a) Decrease in basicity-(fajan’s principle)Larger the size of cation, greater is the tendency of such hydroxides to dissociate(weak bond) and stronger will be the base(Covalent nature).

• b) Ionic radii of post lanthanoids• The element which follow the lanthanoids in the

third transition series are known as post lanthanoids.

• The ionic radii of the element which follow lanthanium(Hf, Ta, W, etc) are similar to that of the element of previous period.

• There is normal increase in size Sc to Y to La.


Group Series ↓ 4 5 6 7

1st transition Ti(132pm) V(122pm) Cr(106pm) Mn(94pm)

2nd transition Zr(145pm) Nb(134pm) Mo(129pm) Tc(114pm)

3rd transition Hf(144pm) Ta(134pm) W(130pm) Re(114pm)


This are similar no. of valency and property is called chemical twins.

Actinoids

• 7 period and actinide series.• Electron enter in 5f orbital.• Many physical and chemical property are

similar to actinium(actinoids).• Second inner transition element.• Outermost and penultimate shell remain the

same.• General E.C 5f1-10 6d0-1 7s2

Actinide

• Np(93)- Neptune Pu(94)

Trans-uranic element

• Manmade element atomic no. higher then uranium-92.

Electronic configuration• Ac (89)-

1s22s22p63s23p63d104s24p64d105s25p64f145d106s26p6

6d17s2.• [Rn]- 86• 1s22s22p63s23p63d104s24p64d105s25p64f145d106s26p6

• Ac electronic configuration is• [Rn] 6d17s2 or [Rn] 5f0 6d1 7s2

• 6d and 7s electron is same only 5f electron change by increasing order. Th(90)- [Rn] 5f1,…….. 5f10.

Electronic configuration

Oxidation state of actinoids• Common oxidation state is +3.• Np+3, Pu+3 get oxidised Np+4,Pu+4 in aqs

soln. some become stable some unstable.Ac Th Pa U Np Am Cm Bk Cf Es Fm Md No Lr2 2 23 3 3 3 3 3 3 3 3 3 3 3 3 34 4 4 4 4 4 4 4

5 5 5 5 56 6 6 6

7 7

Comparison between lanthanoids and actinoids

f block element

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