# 19.5B: Paramagnetism

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## Magnetism

In CHEM1902 (C10K) we introduced the formula used to relate the magnetic moment to the number of unpaired spins in a transition metal complex.

μs.o. = √{4S(S+1)} B.M.

During the laboratory session you will carry out a measurement of the magnetic susceptibility which is a measure of the force exerted by the magnetic field on a unit mass of the sample under investigation. This is related to the number of unpaired electrons per unit weight and hence per mole and in the simplest picture we consider that this is solely dependent on the presence of unpaired electrons.

For a Ti(III) complex with 1 unpaired electron this corresponds to:

μs.o. = 2 √ (1/2 (1/2 + 1)) B.M
μs.o. = √ (3) B.M.
μs.o. = 1.73 Bohr Magneton

We will see later that while the spin-only approximation works in many cases, for a more complete analysis it is necessary to consider the contribution made by the orbital motion of the electron as well.