The bonding of a model dimer is analyzed and the physical meaning of the VB-CI responsible for binding is interpreted. Then the electronic structure of transition metal dimers is analyzed and it is concluded that these are held together by ns-gas pairs which interact with the (n-1) d-groove pairs or electrons in a way determined by the electronic nature of the constituent atoms. Next a transition is made to the solid, which is envisioned as an aggregate of dimers where the electric field of all the atomic cores causes breakage of a fraction of the gas pairs. The next step is the interpretation of resistivity: high resistivity is associated with gas pairs which interact strongly with groove pairs and the core, while good conductors have the gas pairs disengaged from them. The final conclusion is that superconductivity is a phenomenon expected from metals with gas pairs which are neither too tightly bound to the core and to groove pairs (poor conductors) nor disengaged from them (good conductors). This sets the stage for an interpretation of high T c superconductivity in ceramics, presented in a following paper.