Paramagnetic: atoms/ions with unpaired electrons — attracted by magnetic field. Diamagnetic: all electrons paired — weakly repelled. Magnetic moment mu = sqrt(n(n+2)) BM, where n = number of unpaired electrons. Examples: $Fe^{2+}$ = [Ar]3$d^6$ has 4 unpaired e-, mu = sqrt(24) = 4.9 BM. $Zn^{2+}$ = [Ar]3$d^{10}$ has 0 unpaired e-, diamagnetic. $Ti^{3+}$ = [Ar]3$d^1$ has 1 unpaired e-, mu = sqrt(3) = 1.73 BM. To find unpaired electrons: write the electronic configuration of the ion (remove 4s before 3d), count electrons in the partially filled subshell, apply Hund's rule.