On the basis of behaviour in a magnetic field, substance are classified as paramagnetic, diamagnetic and ferromagnetic. Those substance which are attracted by the applied magnetic field are called paramagnetic where as those which are repelled by the magnetic field are called diamagnetic. Substances which are very strongly attracted by the applied field are called ferromagnetic.
Paramagnetism is a property due to the presence of unpaired electrons. Thus most of the transition metals are paramagnetic. As the number of unpaired electrons increases, the paramagnetic character also increases.
The magnetic moment is calculated from the following formula μ = √n(n+2) BM
where n is the number of unpaired electrons and B. M stands for Bohr magneton.
Illustration 10:Why does Mn(II) show maximum papamagentic character amongst the bivalent ions of the first transition series?
Solution:Mn2+ has maximum number of unpaired electrons i.e. 3d5.
Illustration 11:A substance is found to have a magnetic moment of 3.9 B.M. How many unpaired electrons does it contain?
Solution:Using the formula, μ = √n(n+2), B.M. n = 3
Catalytic Properties
Many transition metals and their compounds have catalytic properties. For e.g. V2O5, Fe, FeCl3, Ni, Pd etc.
This property of transition elements is due to their variable oxidation states. In some cases the transition metals with their variable valency may form variable unstable intermediate compounds. In other cases the transition metal provides a suitable reaction surface.
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