<P> Polar molecules must contain polar bonds due to a difference in electronegativity between the bonded atoms . A polar molecule with two or more polar bonds must have a geometry which is asymmetric in at least one direction, so that the bond dipoles do not cancel each other . </P> <P> Polar molecules interact through dipole--dipole intermolecular forces and hydrogen bonds . Polarity underlies a number of physical properties including surface tension, solubility, and melting and boiling points . </P> <P> Not all atoms attract electrons with the same force . The amount of "pull" an atom exerts on its electrons is called its electronegativity . Atoms with high electronegativities--such as fluorine, oxygen, and nitrogen--exert a greater pull on electrons than atoms with lower electronegativities such as alkali metals and alkaline earth metals . In a bond, this leads to unequal sharing of electrons between the atoms, as electrons will be drawn closer to the atom with the higher electronegativity . </P> <P> Because electrons have a negative charge, the unequal sharing of electrons within a bond leads to the formation of an electric dipole: a separation of positive and negative electric charge . Because the amount of charge separated in such dipoles is usually smaller than a fundamental charge, they are called partial charges, denoted as δ + (delta plus) and δ − (delta minus). These symbols were introduced by Christopher Kelk Ingold and Edith Hilda Ingold in 1926 . The bond dipole moment is calculated by multiplying the amount of charge separated and the distance between the charges . </P>

How does oxygen play a role in polarity