Well I do know that a coordinate number is the number of atoms surrounding an atom in a solid state lattice
And for the second bit, I assume LiCl would have a larger lattice energy due to the greater difference in electronegativity of both consituents, similar with the next one. Not sure...
How would I go about deriving the cooridinate numbers of both ions in rock salt, and,
how could I account for the differences in lattice enthalpy between the following;
LiCl (861 kJ/mole) - NaCl (787)
LiCl - LiF (1046)
LiCl - MgO (3850)
Cheers.