Question

Which is more important in determining a compound’s melting points, polarity or molar mass? Why?

Answer 1

in determining a compound's melting points, polarity is more important

Every compound is contained by molecules.

Polarity determine how much energy is needed to break these molecules, meanwhile molar mass only determine the weight of the molecules. Even though molar mass do affecting the boiling point, it's not as much as the basic resistance of the separation of inter molecular forces does.

Answer 2

Both polarity and molar mass affect the melting points of a compounds. However, polarity is more prioritized for compounds of similar molar mass. The order of increasing melting point follows: non-polar < polar < ionic.

Ionic compounds have the strongest forces holding them which is why it requires higher temperature to overcome those forces. Next, polar substances have weaker electrostatic forces than ionic compounds, but have stronger forces than non-polar compounds due to the presence of dipole-dipole interaction. The force present in non-polar compounds is Van Der Waals forces.