How does density affect melting point?
Short answer: It isn't a major factor in determining melting point.
Here is a table of compounds with their densities and melting points.
Compound; Density/g·mL⁻¹; mp/°C
hexane; 0.65; -95
ethanol; 0.79; -114
water; 1.00; 0
chloroform; 1.48; -64
dimethyl ether; 1.97; -141
sodium chloride; 2.16; 801
methyl iodide; 2.28; -66
mercury; 13.59; -39
The density increases as we go down the list, but the melting points vary all over the map.
The intermolecular attractions are much more important factors in determining the melting point.