f-block elements Class 12th Notes

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In two series of f-block element, i.e. 4f– and 5f– series known as lanthanides and actinides. These have 14-14 elements are present respectively.

Lanthanides- The 14 elements after lanthanum are called lanthanides in which 4 f-orbitals are progressively filled. General configuration of lanthanoids is 4f1-14 5d0-1 6s2.

All lanthanide shine like silver and are soft metals. Many of the lanthanides are coloured in solid or in liquid state. Lanthanides generally combine with chelate ligands to form ring compounds.

Oxidation state– The most common oxidation state of lanthanoid is +3. However, Ce shows +4, Eu shows +2 and Yb shows +2 oxidation state because they acquire stable configuration.

Lanthanide contraction– As the nuclear force increases from La to Lu the radii of atom and ion decreases, this property is known as lanthanide contraction. It is a unique feature in the chemistry of the lanthanoids. This contraction occurs due to poor shielding by f-electrons.

Characteristics of Lanthanides

  • All lanthanides are silvery white, and soft metals.
  • Their melting point ranges between 1000 to 1200K.
  • These metals combine with hydrogen, when heated.
  • They tarnish rapidly in air.
  • Earlier members if this series are quite reactive, similar to calcium.

Actinides– The elements after actinium are called actinides in which 5f-orbitals are progressively filled. General configuration of actinides is 5f1-14 6d0-1 7s2.

Oxidation state– Partially the gnergies  of 5f, 6d and 7s are comparactive. Actinides generally show +3 oxidation state. The elements in the first half of the series show higher oxidation state.

Characteristics of Actinides

  • All actinides are strong reductant.
  • Actinides have greater tendency to form complex ions as compered to lanthanides.
  • Actinides can react with O2, H and S like lanthanides.

Some Application of d– and f-block Elements

  • Cr, Mn and Zn etc. also form many important alloys.
  • Alloys of iron are most important materials for various constructions.
  • Cu, Au and Ag are called coinage metals.
  • Some metals and their compounds are used as catalyst e.g. Fe/V2O5 etc.

 

 

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