Quantum jumps light comes out of the atom

The electrons in Bohr's model do not spiral inwards continuously, but can only drop from an orbit of higher energy to one of lower energy. Rather than the continuous loss of energy expected from classical physics, the loss is sudden, carried away by a light photon of energy hf, exactly equal to the energy difference between the initial and final orbits. What we see is a spectrum of discrete wavelengths corresponding to transitions between different orbits. Since the allowed orbits differ from atom to atom, we see a spectrum of frequencies characteristic of the element.

Hydrogen has a characteristic 'fingerprint'; so has helium, and so has iron when vaporised to a high temperature. By the light emitted from a sample we can recognise minute traces of elements, even if the source of light is inaccessible, such as a distant star.

12.1.5 The lowest orbit

When n = 1 the atom is in its state of lowest energy, called the ground state. It cannot lose energy, and therefore does not emit light. There is nowhere for the electron to go and therefore it remains in the ground state indefinitely. The quantum condition ensures that we have a stable universe!

The simplest atom is the atom of hydrogen. It has just one electron in orbit around a proton. At a sufficiently high temperature the atom is in an excited state, with the electron in one of the higher orbits. When the electron makes a quantum jump from a higher to a lower orbit, a photon of light is emitted of energy Quantum jump.

hf = El - Ef where Ei = energy of initial state, and Ef = energy of final state.

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