How do polar molecules differ from nonpolar molecules?
Polar molecules differ from nonpolar molecules by having positive and negative ends and stronger intermolecular forces of attraction.
A polar molecule such as water has a negative end and two positive ends. The charged end of one molecule is attracted to the oppositely charged end in a neighbouring molecule.
Polar molecules have strong intermolecular forces of attraction. It takes more energy to separate the molecules from each other, so polar substances have relatively high melting points and boiling points.
A nonpolar molecule such as BF₃ is symmetrical about the centre of the molecule, so the molecule has no positive or negative end. Each charge around the central atom is balanced, and there is no overall polarity to one side of the molecule. The molecule is nonpolar.
Nonpolar molecules have only weak attractive forces for each other, so nonpolar substances tend to have low melting points and boiling points.