There are two main types of electron configurations: the spdf notation and the numerical representation like 2 8 8 2. The spdf notation refers to the symbols of orbitals, while the numerical format indicates the total number of electrons in each shell. The Bohr model outlines electron configurations based on major energy levels, with a maximum capacity for electrons determined by the formula 2n². For instance, calcium (element #20) has a configuration of 2, 8, 8, 2, reflecting the filling of these energy levels. In contrast, the spdf configurations are derived from the Schrödinger Quantum Model and follow the Aufbau Principle, which dictates that electrons fill the lowest available energy levels first. Understanding these configurations requires knowledge of atomic models and their historical development, which can provide deeper insights into the evolution of electron configurations.