In this paper we consider some concepts that are part of standard chemistry from a formal point of view. Usually, concepts and theories of chemistry are presented in an informal way (not in an axiomatic way), and this move may present some philosophical diffculties (although chemistry itself - so as the other disciplines of applied science - does not seem to suffer with these diffculties). Here, we shall concentrate in the indiscernibility of some basic objects dealt with in chemistry, such as atoms, molecules, and their components, and we shall deal with their formal counterparts too. We begin with a general view about the identity of such elements and of their components, and then we show why the notion of identity of chemical objects is problematic with respect to the notion of identity of standard logic and mathematics (which by hypothesis underlies chemical theories). We suggest that, on the other hand, chemistry seems to suppose that some of these basic objects must be 'identical' (indistinguishable) from one another (as emphasized long time ago by John Dalton, as we shall see). On the other hand, from a formal point of view, if the underlying logic of atomic theory is classical logic (which is also the background for standard mathematics), identical things must be one and the same thing and, therefore, must collapse in just one thing. This apparent contradiction can be dealt with from different perspectives, and here we propose the use of a non-standard set theory (namely, quasi-set theory) to ground an axiomatic formulation of certain chemical theories, showing that such a move may lead us to a view closer to what says. Since this theory is not well known, a brief revision is necessary. Finally, we show how is it possible to consider mathematical models for atoms and molecules by using quasi-set theory, thus avoiding the logical problem mentioned above, and we discuss a little a mereological approach to chemical compounds by considering this quasi-set theoretical view.
indiscernibility; non-individuals; quasi-sets; chemical elements
