It does this by giving out light as illustrated in Figure 212. In order to return to lower energy levels, the electron must lose energy. Each element has its own characteristic line spectrum that can be used to identify it.Ĩ Line Spectra When an atom is excited its electrons gain energy and move to a higher energy level. This is known as a line spectrum and is illustrated in Figure211. Instead, it comprises very bright lines of specific colours with black space in between. This is the basis of the ‘flame tests’ for metals.ĥ Flame Tests for Metals For example, the alkali metals all impart a characteristic colour to the flame:lithium - red, sodium - yellow, potassium – lilac, this is the basis of atomic absorption spectroscopy If the light is passed through a spectroscope, containing a prism or diffraction grating, to separate out the different colours,then what is observed is not a continuous spectrum (like a rainbow) as is observed with normal ‘white’ light, which contains all frequencies. For many metals the same effect can be observed when their compounds are heated directly in a Bunsen flame. In the case of gases this can be achieved by passing an electrical discharge through the gas at low pressure. When an element is excited it will often emit light of a characteristic colour (e.g. The best evidence for the fact that electrons in an atom surround the nucleus in certain allowed energy levels, or orbitals comes from a study of the emission spectra of elements. Familiar visible light is just the very small region of this spectrum that our eyes happen to be sensitive to.ĭecreasing frequency Decreasing energy of quantaģ Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom. This covers radiation from gamma rays through to radiowaves, as illustrated in Figure 210 below, that has many properties in common. Here the term “light” is being used rather loosely to indicate electromagnetic radiation. The study of the emission of light by atoms and ions is the most effective technique for deducing the electronic structure of atoms. Presentation on theme: "Atomic Emission Spectra"- Presentation transcript:
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