# Why is the melting point of BaCl2 > BeCl2 while CsCl<NaCl

I'd think that increasing ionic character by increasing electronegativity difference would result in strong bonds but in the case of NaCl and CsCl(and the other chloride of the group) the case is different.

• Sep 17 '17 at 9:09
• Ionic compounds have no bonds. It's a question of efficient packing and electrostatics.
– Karl
Sep 17 '17 at 9:34
• @Karl Ionic compounds have bonds, just constructed differently from those th things like water and methane. Sep 17 '17 at 9:46
• @OscarLanzi A "bond" implies directional connection. No such thing in sodium chloride. The term is simply not helpful in explaining the properties of ionic compounds, as can be see by the above question, where it has mislead the OP.
– Karl
Sep 17 '17 at 10:49
• @Karl A bond does not imply directionality. An ionic bond is a perfectly valid bond whether you are discussing the 'real' ionic bond (with non-zero covalent/metallic character), or the ideal 'pure' ionic bond. Since this is an issue of chemical definitions, I refer you to the IUPAC Gold Book. Sep 17 '17 at 11:45

When comparing barium chloride and beryllium chloride, you are essentially comparing apples and oranges since beryllium chloride is a primarily molecular compound. In its gas phase, it forms $\ce{BeCl2}$ monomers and $\ce{Be2Cl4}$ dimers. The intramolecular attractions in molecular compounds are typically rather strong with the intermolecular ones are weaker. For ionic compounds such as barium chloride, we cannot distinguish between the two since we cannot define molecular entities.