This work describes the concept of bond order. It shows that covalent bond energy is correlated to bond order. Simple expressions which included bond order are introduced to calculate bond energies of homo-nuclear and hetero-nuclear bonds. Calculated values of bond energies are compared with literature values and show there is very good agreement between and calculated and experimental values in the vast majority of cases. Bond order reveals the strength of a bond and shows the number of bonds in both (...) homo-nuclear and hetero-nuclear covalent bonds. (shrink)