question_answer

  The ions of NaF and MgO have the same number of electrons and inter nuclear distances are about the same (235 pm and 215 pm). Why are then the melting points of NaF and MgO so different (992°C and 2642°C)?

Answer:

                  In MgO, both the ions are divalent in nature (\[M{{g}^{2+}}\] and \[{{O}^{2-}}\]) while in NaF, these are of monovalent nature (\[N{{a}^{+}}\] and\[{{F}^{-}}\]).The electrostatic forces among the ions in the crystal lattice of MgO are stronger than in case of NaF. Therefore, the melting point of MgO is higher (2642°C) as compared to NaF (992°C).