This can induce at dipole in a neighbouring molecule, creating a temporary dipole-temporary dipole attraction. At any one instant, the electrons may be unevenly distributed, creating an instantaneous dipole within the molecule: one pole is delta negative, while the other is delta positive. These form more often when the molecule has a large electron cloud (you can predict this from its molar mass). Non-polar molecules can also have temporary dipoles. The attraction between the delta negative pole of one molecule and the delta positive pole of a neighbouring molecule is called a permanent dipole-permanent dipole attraction. This is due to an asymmetrical shape (due to lone pairs of electrons around the central atom) and/or due to the presence of polar-covalent intra-molecular bonds (electronegativity difference between the two atoms of 0.5+), which do not "cancel out" each other.Īs there is an asymmetrical charge distribution, one side ("pole") of the molecule has a slight ("delta") negative charge, while the other pole has a delta positive charge. Polar molecules have an asymmetrical electron cloud/charge distribution. Permanent dipole-permanent dipole interactions These dipoles may be permanent (polar molecules) or temporary (instantaneous or induced dipoles in non-polar molecules). The first thing required for there to be dipole-dipole interactions between molecules is for both molecules to have a dipole.
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