The electronegativity of an atom is its ability to attract additional electron density. If an atom has a high electronegativity value, it easily attracts additional electrons. An atom with low electronegativity easily releases electrons. Ionic bonds are formed between atoms with a large difference in electronegativity. Atoms that have similar electronegativities tend to form covalent bonds. If the difference in electronegativity is neither small nor large, the bond formed is covalent with ionic properties. The electrons are shared as in a covalent bond, but they also tend to be located closer to the atom with the higher electronegativity, as in an ionic bond. Thus one of the atoms appears to be slightly negative and the other appears to be slightly positive. The existence of these opposite partial charges at a small distance from each other creates a dipole. Where q is the magnitude of the charge and d is the distance between the charges, the dipole moment m is defined as
Since the atoms were originally electrically neutral, any positive charge created in the dipole must be equally balanced by a negative charge in the dipole. Thus the quantity q is the magnitude of either the positive or the negative charge. The dipole
moment is actually a vector with magnitude q and direction d. By convention, the
