Chapter 11, Problem 141RQ

Melting point is sometimes used as an indication of the extent of ionic bonding in a compound—the higher the melting point, the more ionic the substance. On this basis, oxides of metals seem to become less ionic as the charge on the metal ion increases. Thus, ${\text{Cr}}_{\text{2}}{\text{O}}_{\text{3}}$ has a melting point of $\text{2266 °C}$ while ${\text{CrO}}_{\text{3}}$ has a melting point of only $\text{196 °C}$. The explanation often given is similar in some respects to explanations of the variations in the strengths of certain intermolecular attractions given in this chapter. Provide an explanation for the greater degree of electron sharing in ${\text{CrO}}_{\text{3}}$ as compared with ${\text{Cr}}_{\text{2}}{\text{O}}_{\text{3}}$.