2. Invar effect

A number of physico-chemical and mechanical properties can be explained by considering the forces of interaction between atoms. A simplistic approach to illustrate this is to consider just two atoms, i and j, whether they are the same or different; far apart and brought together. The interaction energy between metallic atoms (metallic bond) can be estimated by analogy with the case of covalent bonds. In the case of covalent bonds, the forces are central, i.e. oriented in the direction of the bond between the two atoms. Given the spatial distribution of electric charges (electrons and protons) specific to each atom, when the two atoms come together, there is an electrostatic attractive force resulting from charges of opposite sign, and a repulsive force occurring at short distances between charges of the same sign. The energies of attraction U _a ...