Class 12 Chemistry D and F Block Elements Magnetic Properties

Magnetic Properties

Substances, depending on their behaviour in an external magnetic field, are classified into 2 types:


  • They are weakly attracted on application of magnetic field due to presence of one or more unpaired electrons that gets attracted by the magnetic field.
  • Application of a magnetic field magnetizes the paramagnetic substances in the same direction but lose their magnetism in the absence of magnetic field.
  • O2, Cu2+, Fe3+, Cr3+ are some examples of such substances.

Fig. A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetism.



  • They are weakly repelled by a magnetic field due to the absence of unpaired electrons.
  • They are weakly magnetized on application of magnetic field in opposite direction.
  • Pairing of electrons cancels out their magnetic moments and they lose their magnetic character.
  • For example, H2O, NaCl and C6H6 are some examples of such substances.

In 3d series the orbital angular momentum of the electrons of the elements is less due to which they exhibit less contribution.

The magnetic moment for these elements is calculated using the spin only formula

μ = √(n(n+2))

Where n = number of unpaired electrons

μ = magnetic moment in units of Bohr Magneton (BM).


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

SOLUTION:  Z = 27 = [Ar] 3d7 4s2

M2+ = [Ar] 3d7

This means that it has 3 unpaired electrons.

n = 3


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