Final answer:
The strength of the attractive forces between particles in a crystal determines its melting point. Molecules with weak attractive forces have low melting points, while those with strong attractive forces have high melting points.
Step-by-step explanation:
The melting point is a metric of the energy required to transform the solid phase of a substance into a liquid. Generally, the stronger the bond between the atoms of an element, the more energy required to break that bond. The melting points exhibit comparable, albeit more complex, periodic trends as observed in the atomic radii. Molecules with weak attractive forces form crystals with low melting points. Crystals consisting of particles with stronger attractive forces melt at higher temperatures.