Light, Photon Energies, and Atomic Spectra

Fireworks displays are fascinating to watch. Neon lights and sodium vapor lamps can transform the skyline of a city with their brilliant colors. The eerie phenomenon of the aurora borealis is an unforgettable experience when you see it for the first time. All of these events relate to the generation of hght and its transmission through space. 

Wavelength (A), the distance between two consecutive crests or troughs, most often measured in meters or nanometers (1 run = 10 m). 

Frequency (i ), the number of wave cycles (successive crests or troughs) that pass a given point in unit time. If 10 cycles pass a particular point in one second, 

The frequency unit hertz (Hz) represents one cycle per second. 

The speed at which a wave moves through space cem be found by multiplying the length of a wave cycle (A) by the number of cycles passing a point in unit time (v). For light, 

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If we accept that light exists as photons, then the presence of specific and sharp frequencies in the emission spectra of atoms must be interpreted as restricting the internal energy of atoms to specific values. For single-electron atoms the frequencies of the observed photons satisfy the simple relationship... 

The lines in the emission and absorption spectra of the atoms correspond to the electronic transitions as electrons move from one orbital to another. The energy of the photon emitted, or absorbed, corresponds to the difference in energies of the electron in the two orbitals involved. The yellow/orange glow of sodium lamps or street lights corresponds to the photons emitted as excited sodium atoms with the outermost electron in the Ap orbital fall down to the ground atomic state in which it is in the 3s orbital. 

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