Hydrogen bonds are found between fluorine, oxygen and nitrogen atoms when each try to bind with a hydrogen bond. Because of the size difference between the atoms, the attraction of electrons becomes unequal. In the case of water, since the oxygen atom has a heavier and greater nucleus, the pull on the electron from the oxygen nucleus is greater compared to that of the hydrogen. Therefore the shared electrons between the two atoms are located a bit closer to the oxygen nucleus, creating a dipole moment. Hydrogen bonding in water is why water has a relatively high heat of vaporization and specific heat capacity.