Polar

Polar molecules (such as water) carry dipole charges (slight positives and negatives) meaning that they tend to be very good solvents and have higher than predicted boiling points. The polar ends of the molecule are created because the electrons floating around the molecule tend to move toward a certain element of the molecule (in order to complete its outer shell and bonding requirements) leaving for example the hydrogens of water lacking in electrons (delta +ve) and the oxygen of the water slightly gaining in electrons (delta -ve).

Polarity is determined by the electronegativity of the elements within the molecule. For example in water, Oxygen has a higher electronegativity than Hydrogen so the shared electrons within the molecule are drawn to the oxygen atom more than two hydrogen atoms. Since the negatively charged electrons have moved towards the oxygen it becomes slightly negative and the hydrogen slighlty positive.