Example 4.7

Example . attracted very strongly are said to be ferromagnetic . In fact, ferromagnetism is an extreme form of paramagnetism. Many of the transition metal ions are paramagnetic. Paramagnetism arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is of no significance. For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the ‘spin-only’ formula, i.e.,   n n   where n is the number of unpaired electrons and µ is the magnetic moment in units of Bohr magneton (BM) . A single unpaired electron has a magnetic moment of . Bohr magnetons (BM). The magnetic moment increases with the increasing number of unpaired electrons. Thus, the observed magnetic moment gives a useful indication about the number of unpaired electrons present in the atom, molecule or ion. The magnetic moments calculated from the ‘spin-only’ formula and those derived experimentally for some ions of the first row transition elements are given in Table . . The experimental data are mainly for hydrated ions in solution or in the solid state. Sc Ti . . Tl . . . . . . . . . . – . Co . . – . Ni . . – , Cu . . – . Zn Ion Configuration Unpaired electron(s) Magnetic moment Calculated Observed Table . : Calculated and Observed Magnetic Moments (BM) Calculate the magnetic moment of a divalent ion in aqueous solution if its atomic number is . With atomic number , the divalent ion in aqueous solution will have d configuration (five unpaired electrons). The magnetic moment, µ is   .92BM   