 A further issue is the detailed understanding of the cause of chemical bonding. For many years, the dominant view, based on the Hellman-Feynman theorem, has been that it is essentially an electrostatic attraction between positive nuclei and negative electron clouds (Feynman 1939). But an alternative, originally suggested by Hellman and developed by Rüdenberg, has recently come into prominence. This emphasizes the quantum mechanical analogue of the kinetic energy (Needham 2014). Contemporary accounts may draw on a number of subtle quantum mechanical features. But these details shouldn’t obscure the overriding thermodynamic principle governing the formation of stable compounds by chemical reaction. As Atkins puts it,