Abstract
The assignment of four quantum numbers to the so called differentiating electron, considered as the last to be “located” in the electronic configuration of an atom, may help to confuse electrons with the spin-orbitals used to obtain a good approximation to the poliatomic atom wave function. But, using those four quantum numbers to deduce which is the atom concerned is an artificial unnecessary problem based in arbitrary rules which, furthermore, leads to failures when the electronic configurations are exceptions to the aufbau, a case very frequent among the transition elements, the lantanides and the actinides. Instead of helping to understand the atomic electronic structure, this problem is very capable of arising severe conceptual errors. Therefore, its inclusion in learning programs of secondary school chemistry should not be encouraged.