Atomic model for emission and absorption of radiation

An atom is made of a nucleus and one or more electrons. The electrons move in some way around the nucleus. The electrons (and therefore the atoms) may be excited, or given more energy than they usually have, for example by shining light on them. This absorption of energy from light is the cause of absorption spectra. When the excited electrons give up their extra energy, and return to their normal non-excited state, light may be given off. That is the cause of the emission spectrum. The wavelength of light emitted or absorbed depends on the energy emitted or absorbed by the atom. The fact that only definite wavelengths are emitted or absorbed implies that the atom has only definite energy states available to it. The atom's energy is said to be "quantized". Atoms of different elements have different quantized energies, therefore, emit and absorb different characteristic wavelengths.