The interatomic or intermolecular forces are usually represented in terms of a potential energy function V(r) such that F(r) = −dV(r)/dr. For neutral particles, at large internuclear distances, there is a slight attractive potential between the particles called the van der Waals potential (which is the long-range part of the Lennard-Jones potential). For like atoms or molecules in like states the van der Waals interaction potential can be represented by

where C is a constant (which depends on the type of particle), a_o is the Bohr radius (0.0529 nm), and Ry denotes the Rydberg energy unit (13.605 eV). Calculate the van der Waals force of attraction between two hydrogen molecules (for which C = 24.0), and compare with the coulomb force between a proton and an electron at a distance r = Na_o, where N ≫1.

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V(r) = -C(ao/r)6 Ry