Strontium, atomic spectrum

Each element s atomic emission spectrum is unique and can be used to determine if that element is part of an unknown compound. For example, when a platinum wire is dipped into a strontium nitrate solution and then inserted into a burner flame, the strontium atoms emit a characteristic red color. You can perform a series of flame tests yourself by doing the miniLAB below. 

In general, excited atoms emit spectral lines, i.e. the radiation lies in very narrow wavelength ranges of width 10 to 10 nm. In practice, atomic resonance lines from species, such as strontium in a red star, contribute little to the visual effect since the emission falls in the short wavelength part of the spectrum (this line may be observed in a Bunsen burner flame at 461 nm). 

The best flame emission in the red region of the visible spectrum is produced by molecular strontium monochloride, SrCl. This species - unstable at room temperature - is generated in the pyrotechnic flame by a reaction between strontium and chlorine atoms. Strontium dichloride, SrCl 2, would appear to be a logical precursor to SrCl, and it is readily available commercially, but it is much too hygroscopic to use in pyrotechnic mixtures. 

Line spectra occur when the radiating species are individual atomic particles that are well separated, as in a gas. The individual particles in a gaseous medium behave independently of one another, and the spectrum in most media consists of a series of sharp fines with widths of 10 to 10 - A (10 to 10 nm). In Figure 24-19, fines for sodium, potassium, strontium, calcium, and magnesium are identified. 

Figure 7.7 The line spectra of several elements. A, A sample of gaseous H2 is dissociated into atoms and excited by an electric discharge. The emitted light passes through a slit and a prism, which disperses the light into individual wavelengths. The line spectrum of atomic H is shown (top). B, The continuous spectrum of white light is compared with the line spectra of mercury and strontium. Note that each line spectrum is different from the others.

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