Bond dipole moment

Separation of charge in the HF molecule

Molecules such as hydrogen fluoride, HF, are polar because, as shown in the image, the covalent bond that is formed between the H and F atoms have a separate of charge.

Polar molecules interact with an electric field.

The separation of charge in a polar covalent bond creates an electric dipole which allows the molecule to interact with an electric field. Another way to indicate the polarity of the bond is to draw the bond dipole moment.

A bond dipole moment is a vector. The direction of the vector is represented an arrow, which always points from the positive end of the bond to the negative end of the bond.

A "+" is placed at the tail of the arrow to indicate the positive end of the bond.

The dipole moment for the hydrogen fluoride molecule is drawn over the H-F bond and points in the direction of the fluorine molecule.

H-F