Final answer:
The quantum mechanical model of an atom focuses on the behavior and characteristics of electrons, using four quantum numbers to describe their probable locations and spins.
Step-by-step explanation:
The quantum mechanical model of an atom focuses on the behavior and characteristics of electrons. In this model, the electrons are not simply revolving around the nucleus in fixed orbits. Instead, their positions are described using four quantum numbers that approximate their locations and spin directions within an atom. This approach is more concerned with the probabilities of where an electron might be found at any given time, based on the electron's energy level and sublevels.