We present a mean-field model for the description of transition or noble metal nano-objects interacting with an environment. It includes a potential given by the second-moment approximation to the tight-binding Hamiltonian for metal-metal interactions, and an additional many-body potential that depends on the local atomic coordination for the metal-environment interaction. The model does not refer to a specific type of chemical conditions, but rather provides trends as a function of a limited number of parameters. The capabilities of the model are highlighted by studying the relative stability of semi-infinite gold surfaces of various orientations and formation energies of a restricted set of single-faceted gold nanoparticles. It is shown that, with only two parameters and in a very efficient way, it is able to generate a great variety of stable structures and shapes, as the nature of the environment varies. It is thus expected to account for formation energies of nano-objects of various dimensionalities (surfaces, thin films, nano-rods, nano-wires, nanoparticles, nanoribbons, etc.) according to the environment.