Binding energy of quarkonium systems and the mass spectra

We show that if a quark (or antiquark) with mass $m_a$ is replaced by a heavier quark (or antiquark) with mass $m_b$ in a quarkonium state, the increase of the mass of the quarkonium system is substantially less than $m_b-m_a$ due to the increase of the binding energy (in some cases it is only $\frac{1}{6}$ of $m_b-m_a$). It is shown that for the heavy quarkonia the $F$-family mesons get close to the $D$-family mesons for a large class of potentials. The spectrum of all known mesons is explained if the change of the binding energy is taken into account.