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• Propanal has (permanent) dipole-dipole forces • Butane has van der Waals’ forces • Strength of intermolecular forces: hydrogen bonds > dipole-dipole > van der Waals (Note - actual values for reference are prop-2-en-1-ol 97°C, propanal 46°C and butane ?1°C) [10] Q3 (a) (i) shared pair of electrons
Van der Waals (VDW) interactions are probably the most basic type of interaction imaginable Any two molecules experience Van der Waals interactions Even macroscopic surfaces experience VDW interactions, but more of this later The physical process that leads to Van der Waals interactions is clear, but it is difficult to
forces can exist for two materials immersed in a fluid a, The interaction between material 1 and material 2 immersed in a fluid (material 3) is repulsive when b, The optical properties of gold (1), bromobenzene (3) and Silica (2) are such that this inequality is satisfied
attractive forces are called van der Waals forces In fact, we must distinguish three types of van der Waals forces: the ori-entation force, the induction force, and the dispersion force, to be described below Orientation forces occur between two molecules with permanent electric dipoles Taking a thermal average of the
van der Waals (vdW) forces exist between any pair of bodies if their material polarizability di?ers from the background 1 ,3–6 41 Additionally, a vdW torque can appear if these bodies display either an anisotropic shape or are birefringent,27 i e , their dielectric properties are di?erent alongdi?erentprincipaldielectricaxes