March is one of the main theoreticians in the field of quantum physics. His initial contributions were related to the understanding of the structure of the electrons of solids, liquid metals and processes relating to transition phases. At the conference organized by the BBV Foundation in 1993, which is transcribed in this book, the speaker presents an assessment of the form in which two useful chemical concepts, links and atomic or molecular fragments, understood as blocks that allow the construction of larger and solid molecules, and electronegativity, can be founded on quantum mechanics. He then argues that both recent progress in theoretical chemistry and the current requirements of this discipline are leading to a fruitful feedback process in the field of physics.