What is the quantum mechanical model

The quantum mechanical model is based on quantum theory, which illustrates that matter also exhibit characteristics related to waves. On the basis of quantum theory, it is impossible to determine the accurate momentum and position of an electron at a similar time. This is called the uncertainty principle.  

The quantum mechanical model of the atom utilizes composite configurations of orbitals, also known as electron clouds, the volumes of space in which there is a probability to be an electron. Thus, in spite of certainty, this model is based on probability.