Explain what ideas led Bohr to suggest a new atomic model; and state Bohr postulates. Explain also, in words, what the correspondence principle is in atomic physics.
Niels Bohr suggested a new atomic model based on a combination of experimental evidence and theoretical considerations. One idea that led Bohr to propose his model was the observation of distinct line spectra emitted from excited atoms. These line spectra indicated that energy is quantized in specific, discrete amounts. Another important idea was the understanding that electrons could only occupy certain energy levels around the atomic nucleus.
Bohr's model of the atom consisted of the following postulates:
1. Electrons orbit the nucleus in specific energy levels or shells, each with a fixed energy value. Electrons are not allowed to have intermediate energies.
2. Electrons can jump from one energy level to another by absorbing or emitting energy in discrete amounts. When an electron moves to a lower energy level, it emits energy in the form of light or electromagnetic radiation. Conversely, when an electron absorbs energy, it jumps to a higher energy level.
3. The angular momentum of an electron in a particular orbit is quantized. This means that the electron's momentum is restricted to specific values, not continuously variable.
The correspondence principle in atomic physics states that the predictions of a new theory should match the results obtained from established theories in the appropriate limit. In other words, if a new theory is more accurate or comprehensive than the existing theory, it should reduce to the predictions of the existing theory when applied to situations where the existing theory is known to be correct.
In the context of Bohr's atomic model, the correspondence principle meant that his model should reproduce the well-established results of classical physics when applied to macroscopic systems. For example, when the energy levels of atoms are large and the motions of electrons are similar to the motions of planets in the solar system, Bohr's model should reduce to the classical laws of motion and electromagnetism.
The correspondence principle helped ensure that Bohr's model did not contradict the existing body of knowledge while still providing an explanation for the observed phenomena at the atomic level.