1 Stronger intermolecular forces â higher melting and boiling points. 2  Viscosity is a measure of how well substances flow. 3  Stronger intermolecular forces â higher viscosity. 4  Surface tension is a measure of the toughness of the surface of a liquid.5  Stronger intermolecular forces â higher surface tension. Viscosity is a measure of how well substances flow. 2  Stronger intermolecular forces â higher viscosity. 3  Surface tension is a measure of the toughness of the surface of a liquid. 4  Stronger intermolecular forces â higher surface tension. 5  This is a small amount of gas that is found above all liquids.