Models of the Atom

The ancient Greeks postulated that matter was made up of invisible units or particles called atoms. We introduce scientific models of the atom in chronological order: Dalton’s model, Thompson’s model, Rutherford’s model, Bohr’s model and the quantum-mechanical model.

Thomson discovered the electron. It was known that electrons were negatively charged, but that matter was electrically neutral. He predicted that electrons are stuck in an equal number of positive charges. Rutherford discovered the atomic nucleus. He created his model in which the electrons orbited the nucleus. Bohr postulated that each orbit has specific energy – the further the orbit is from the nucleus, the more energy its electron has. An electron can gain energy to jump up to energy levels with higher energy. When an electron jumps down, it can lose the energy needed to do this by emitting a photon of the exact energy it needs to shed. 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 ancient Greeks postulated that matter was made up of invisible units or particles called atoms. We introduce scientific models of the atom in chronological order: Dalton’s model, Thompson’s model, Rutherford’s model, Bohr’s model and the quantum-mechanical model.

Thomson discovered the electron. It was known that electrons were negatively charged, but that matter was electrically neutral. He predicted that electrons are stuck in an equal number of positive charges. Rutherford discovered the atomic nucleus. He created his model in which the electrons orbited the nucleus. Bohr postulated that each orbit has specific energy – the further the orbit is from the nucleus, the more energy its electron has. An electron can gain energy to jump up to energy levels with higher energy. When an electron jumps down, it can lose the energy needed to do this by emitting a photon of the exact energy it needs to shed. 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.