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ChemistryEdu Logo d-block Elements | Magnetic, Catalytic and Other Properties#

Magnetic Properties of d-block Elements#

  • Diamagnetic Substances: Diamagnetic substances are repelled by the applied magnetic field.

  • Paramagnetic Substances: Paramagnetic substances are weakly attracted by the applied magnetic field.

  • Ferromagnetic Substances: Ferromagnetic substances are strongly attracted by the applied magnetic field.

  • In d-block elements , paramagnetism arises due to presence of unpaired electrons, each electron having a dipole moment.

  • Magnetic moment is calculated by "spin only" formula:

\[μ = \sqrt{n(n+2)}\]

where, n = Number of unpaired electrons

  • The unit of spin only magnetic moment is Bohr Magneton (B.M).

Formation of Coloured Compounds by d-block Elements#

  • When an electron from a lower energy d-orbital is excited to a higher energy d-orbital, the energy of excitation corresponds to the frequency of light absorbed. This frequency generally lies in the visible region.
  • The colour observed corresponds to the complimentary colour of the light absorbed.
  • The frequency of light absorbed is determined by the nature of ligand.
Ion Sc+3 Ti+4 Ti+3 V+4 V+3 V+2 Cr+3 Cr+2 Mn+3 Mn+2 Fe+3 Fe+2 Co+3 Co+2 Ni+2 Cu+2 Zn+2
Colour Colourless Colourless Purple Blue Green Violet Violet Blue Violet Pink Yellow Green Blue Pink Green Blue Colourless

Formation of Complex Compounds by d-block Elements#

Complex Compounds

Complex compounds are those in which the metal ions bind a number of anions or neutral molecules giving complex species.

Transition elements form a large number of coordination compounds due to:

  • Smaller sizes of metal ions.
  • Availability of d-orbitals for bond formation.
  • High ionic charges.

Examples

  1. \({[Fe(CN)_6]^{3-}}\)
  2. \([Cu(NH_3)_4]^{2+}\)

Catalytic Properties of d-block Elements#

Transition elements are effective as catalysts due to their ability to:

  • adopt multiple oxidation states.
  • form complexes.
Reaction Catalyst
Contact Process Vanadium(V) Oxide
Haber Process Finely divided iron
Catalytic hydrogenation Nickel

Example

Iron(III) catalyzes reaction between iodide and persulphate ion.

\[2I^- + S_2O_8^{2-} → I_2 + 2SO_4^{2-}\]

Step 1.

\[2Fe^{3+} + 2I^- → 2Fe^{2+} + I_2\]

Step 2.

\[2Fe^{2+} + S_2O_8^{2-} → 2Fe^{3+} + 2SO_4^{2-}\]

Formation of Interstitial Compounds by d-block Elements#

  • Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. They are usually non-stoichiometric and are neither typically ionic or covalent.
  • Examples: TiC, Mn4N, Fe3H, VH0.56, TiH1.7
  • Interstitial compounds are very hard and have high melting points than pure metals.
  • Interstitial compounds are chemically inert and have metallic conductivity.

Alloy Formation by d-block Elements#

  • An alloy is a blend of metals prepared by mixing the components.
  • Alloys are formed by atoms with metallic radii that are within about 15% of each other.
  • Because of similar radii and other characteristics of transition metals, alloys are readily formed by these metals. The alloys so formed are hard and have high melting points. Example: Stainless steel
  • Alloys of transition metals with non transition metals are also made. Example: Brass (Copper + Zinc) and Bronze (Copper + Tin).

Questions#

Calculate the magnetic moment of a divalent ion in aqueous solution if its atomic number is 25.

Electronic Configuration of divalent ion with Z = 25 is: 1s22s22p63s23p63d5.

Number of unpaired electrons, n = 5

\[μ = \sqrt{n(n+2)}\]
\[μ = \sqrt{5(5+2)} = 5.92\ BM\]

Calculate the spin only magnetic moment of M2+(aq) ion (Z = 27).

Electronic configuration of M2+(aq): 1s22s22p63s23p63d7.

Number of unpaired electrons, n = 3

\[μ = \sqrt{n(n+2)}\]
\[μ = \sqrt{3(3+2)} = 3.87\ BM\]

Hence, spin only magnetic moment obtained for the given ion is 3.87 BM.