The main difference between the Bohr model of an atom and the quantum mechanical model iBohr model considers an electron to be a particle, quantum mechanics considers it to be a wave. Reason: Though electron has properties of both particles and waves. Bohr considers electron as a particle and in quantum mechanics, it is considered as wave only.

The Bohr model basically described the hydrogen atom with a small positive nucleus and a single electron orbiting like a planet around the sun. The electron could be "excited" by adding energy to the atom, causing the electron to move outward from the nucleus to higher energy levels, then fall back through a series of energy "steps", giving off specific frequencies of radiation on its way back to its original radius called the "ground state.

Two models of atomic structure are in use today: the Bohr model and the quantum mechanical model. The quantum mechanical model is based on mathematics. Although it is more difficult to understand than the Bohr model, it can be used to explain observations made on complex atoms.

A model is useful because it helps you understand what’s observed in nature. It’s not unusual to have more than one model represent and help people understand a particular topic.

The quantum mechanical model is based on quantum theory, which says matter also has properties associated with waves. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle.

The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds), volumes of space in which there is likely to be an electron. So, this model is based on probability rather than certainty.

Four numbers, called quantum numbers, were introduced to describe the characteristics of electrons and their orbitals: