The shape and charge distribution in a water molecule cause it to have a permanent dipole moment which consist of a positive electric charge and a negative charge separated by a distance in space.There are three dipoles in a water molecule. Since O is more electronegative than H the O-H bond is polar. The negative end is at the O atom and the positive end is at the H atom. There are two O-H bonds so there are two bond dipoles. These two bond dipoles are vectors. They combine to form a vector sum with the resultant pointing from the mid-point between the H atoms to the O atom. This resultant is the A dipole moment is a vector quantity and is therefore represented by a small arrow with a tail at the positive center and head pointing towards a negative center. In the case of a Water molecule
If a molecule is completely symmetric then the dipole moment vectors on each molecule will cancel each other out making the molecule nonpolar. A molecule can only be polar if the structure of that molecule is not symmetric.Thus a molecule such as H 2 O has a net dipole moment. We expect the concentration of negative charge to be on the oxygen the more electronegative atom and positive charge on the two hydrogens. This charge polarization allows H 2 O to hydrogen-bond to other polarized or charged species including other water molecules.For molecules there are three types of dipoles Permanent dipoles These occur when two atoms in a molecule have substantially different electronegativity One atom attracts electrons more than another becoming more negative while the other atom becomes more positive. A molecule with a permanent dipole moment is called a polar molecule.
Lets suppose we put water on the xy-plane like so The dipole moment is calculated by looking up the dipole moment contributions from each O-H bond which are polar and summing them to get the net dipole. Each contribution is 1.5 D (debyes). The net dipole points through oxygen down the y-axis in the negative direction.19.08.2011 All these models are point charges and they all have the dipole value of 1.86 D which is the experimental gas phase cluster for water. But I dont understand how Using a water molecule (H 2 O) its possible to calculate the magnitude and direction of the dipole moment. By comparing the electronegativity values of hydrogen and oxygen there is a difference of 1.2e for each hydrogen-oxygen chemical bond.