And of course the same thing holds true for the emission spectra of any other elements, including these ones that we’re also given in this question. That is, if we see an emission spectrum anywhere that looks exactly like this one, then we know that we’re looking at an emission spectrum of helium. What this means is that if we take this helium spectrum, for example, then we know that any helium gas anywhere in the world will produce this exact same emission spectrum with the exact same emission lines at the exact same wavelengths. The important thing to realize is that an emission spectrum kind of acts like a fingerprint for a particular element. Now, since we can see that there’s a whole load of lines in this emission spectrum, we’re not going to individually read off the wavelength of every single one. Meanwhile, the wavelength of this line is about 565 nanometers. So, for example, we can see that this emission line here from the spectrum of the unknown gas has a wavelength of about 454 nanometers. At the top of this figure, we’ve got a wavelength scale, which allows us to read off the wavelength of each of these emission lines. If we look at our unknown gas spectrum, we can see a load of these bright lines, which are emission lines of this particular gas. What we need to do then is to identify a match between this emission spectrum of the unknown gas and one of these five known emission spectra. But rather it’s entirely one of these five elements whose emission spectra were shown here. That is, it’s not a mixture of some number of different elements. Since we’re asked which one of these five elements the unknown gas is, this means we know that the unknown gas must be a pure sample. We’re being asked to identify which of these five elements is the unknown gas. Then, below this, we’ve got the emission spectra of helium, oxygen, neon, argon, and xenon, each of which is a pure gaseous element. Up at the top, we’ve got the spectrum of the unknown gas that the scientist wants to identify. Taking a look at this figure that we’ve been given, we can see that we’ve got a series of emission spectra. Which of the five elements is the unknown gas? Also shown in the figure are the emission spectra of five pure gaseous elements. In order to identify the gas, he looks at the spectrum of visible light emitted from it when it is heated. Fortunately, computer modeling allows researchers to tell many different elements and compounds apart even in a crowded spectrum, and to identify lines that appear shifted due to motion.A scientist has a sample of an unknown gas. Other factors, such as motion, can affect the positions of spectral lines, though not the spacing between the lines from a given element. The more elements an object contains, the more complicated its spectrum can become. The amount of light that is absorbed can also provide information about how much of each element is present. Therefore, a dark line appears in the spectrum at that particular wavelength.īecause the wavelengths at which absorption lines occur are unique for each element, astronomers can measure the position of the lines to determine which elements are present in a target. An electron can release this light in any direction, so most of the light is emitted in directions away from our line of sight. When they emit the energy, they release photons with exactly the same wavelengths of light that were absorbed in the first place. But the electrons want to return to their original levels, so they don’t hold onto the energy for long. This is absorption, and each element’s electrons absorb light at specific wavelengths (i.e., energies) related to the difference between energy levels in that atom. But when photons carrying energy hit an electron, they can boost it to higher energy levels. Every atom has electrons, and these electrons like to stay in their lowest-energy configuration. That fingerprint often appears as the absorption of light. Identifying those fingerprints allows researchers to determine what it is made of. Every element - and combination of elements - has a unique fingerprint that astronomers can look for in the spectrum of a given object. This spread-out light is called a spectrum. Today, this process uses instruments with a grating that spreads out the light from an object by wavelength. The most common method astronomers use to determine the composition of stars, planets, and other objects is spectroscopy. How do scientists determine the chemical compositions of the planets and stars?
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