Light as a Wave

Second Type of Radiation: Emission Line Radiation

• The nucleus of an atom contains its protons and neutrons. Circling around the nucleus (in orbitals) are electrons. Since electrons are attracted to the protons, they normally orbit in their lowest energy state (i.e., closest to the nucleus), called the ground state.

• Electrons can only orbit at very specific radii from the nucleus, and these are different for different elements.

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Suppose something collided into an electron orbiting in the lowest energy level. Some of the energy of the collision could kick the electron up to a higher level, or an excited state.

• Suppose something collided into an electron orbiting in the lowest energy level. Some of the energy of the collision could kick the electron up to a higher level, or an excited state.

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• Eventually, when the electron falls back down, it has to give this energy back. It does so by giving off a photon of light.

• Since each orbital has a very specific level, electron transitions between the orbitals emit very specific amounts of energy. The spectrum from this process would not be continuous but discrete

• Ephoton = E2-E1

• E2

• E1

• E3

Ionization and Emission

• Suppose a very high energy photon passes near an atom. If the photon has enough energy, it can kick the electron completely out of the atom, and create an ion. Eventually, the electron will recombine into (some level of) the ion, and cascade its way down to the lowest energy level. Each downward transition will produce a photon with the exact energy of the transition. This is not a continuous spectrum!

• There is light only at very specific energies (i.e., colors) which correspond to the different possible transitions.

• Iron

• Hydrogen