Molar heat capacity in metals and ionic solids

  1. I am doing my revision and noticed that metals all have a molar heat capacity ~25 J/mol/K = 3R. Ionic solids such as NaCl and CaF2 however have different molar heat capacities. (~51 and 72 respectively)

    Why is this? there is no explination that my lecturer gave and I cant find it online but it seems like it probably comes from the basic physics.

    I know that the observed values of c are not the theorised ones so not exactly 3R. But the values above are at room temp and so should just be the Dulong-Petit law.

    So why are they different and is there a way to calculate what it could be via equation? Is it to do with the bonds producing different degrees of freedom?

    any hints/help would be appreciated
  2. jcsd
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