By contrast, a bright emission line is produced when photons from a hot material are detected in the presence of a broad spectrum from a cold source. As the electrons move closer to or farther from the nucleus of an atom (or of an ion), energy in the form of light (or other radiation) is emitted or absorbed.… In this way, the absorption lines in a spectrum give astronomers information about the temperature of the regions where the lines originate. Which photons are emitted depends on whether the electron is captured at once to the lowest energy level of the atom or stops at one or more intermediate levels on its way to the lowest available level. Atoms in a hot gas are moving at high speeds and continually colliding with one another and with any loose electrons. For example, hydrogen has one electron, but its emission spectrum shows many lines. 14. Certain types of broadening are the result of conditions over a large region of space rather than simply upon conditions that are local to the emitting particle. For each element, the following table shows the spectral lines which appear in the visible spectrum at about 400-700 nm. Generally, an atom remains excited for only a very brief time. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Energy levels are designated with the variable \(n\). During the electron-capture process, the atom emits one or more photons. Absorption lines are seen when electrons absorb photons and move to higher energy levels. “The spectral lines for atoms are like fingerprints for humans.” How do the spectral lines for hydrogen and boron support this statement? The presence of nearby particles will affect the radiation emitted by an individual particle. However, the newly populated energy levels, such as n = 4 may also emit a photons and produce spectral; lines, so there may be a 4 -> 3 transition, 4->2, and so on. Still-greater amounts of energy must be absorbed by the now-ionized atom (called an ion) to remove an additional electron deeper in the structure of the atom. Since the energy levels are discrete, only photons of certain frequencies are absorbed. The speed of atoms in a gas depends on the temperature. Broadening due to local conditions is due to effects which hold in a small region around the emitting element, usually small enough to assure local thermodynamic equilibrium. Emission spectra can have a large number of lines. Spectral lines also depend on the physical conditions of the gas, so they are widely used to determine the chemical composition of stars and other celestial bodies that cannot be analyzed by other means, as well as their physical conditions. Science. Spectral lines are often used to identify atoms and molecules. At the much shorter wavelengths of x-rays, these are known as characteristic X-rays. Then they can use this knowledge to identify the elements in celestial bodies. Which type of line is observed depends on the type of material and its temperature relative to another emission source. Let’s look at the hydrogen atom from the perspective of the Bohr model. A hot, diffuse gas produces bright spectral lines ( emission lines ) A cool, diffuse gas in front of a source of continuous radiation produces dark spectral lines ( absorption lines ) in the continuous spectrum. In the Bohr model of the hydrogen atom, the ground state corresponds to the electron being in the innermost orbit. The atom is then said to be ionized. At the temperature in the gas discharge tube, more atoms are in the n = 3 than the n ≥ 4 levels. By the end of this section, you will be able to: We can use Bohr’s model of the atom to understand how spectral lines are formed. We have described how certain discrete amounts of energy can be absorbed by an atom, raising it to an excited state and moving one of its electrons farther from its nucleus. An incandescent lightbulb produces a continuous spectrum. This process explains how line spectra are produced. When we turn off the light source, these electrons “fall” back down from larger to smaller orbits and emit photons of light—but, again, only light of those energies or wavelengths that correspond to the energy difference between permissible orbits. € 1 Explain how line spectra are produced. The intensity of a line is determined by how frequent a particular transition is, so fewer that ten lines … Thus, hydrogen atoms absorb light at only certain wavelengths and produce dark lines at those wavelengths in the spectrum we see. View Answer. The greater the rate of rotation, the broader the line. Suppose we have a container of hydrogen gas through which a whole series of photons is passing, allowing many electrons to move up to higher levels. Studying the line spectra produced by hot gases and absorbed by cooler gases allows us to identify the elements in stars. The intensity of light, over a narrow frequency range, is reduced due to absorption by the material and re-emission in random directions. In this simplified model of a hydrogen atom, the concentric circles shown represent permitted orbits or energy levels. Each photon emitted will be "red"- or "blue"-shifted by the Doppler effect depending on the velocity of the atom relative to the observer. If the transition involved an electron dropping from a higher level into the n = 2 state, the photon was visible. Since the spectral line is a combination of all of the emitted radiation, the higher the temperature of the gas, the broader the spectral line emitted from that gas. Strong spectral lines in the visible part of the spectrum often have a unique Fraunhofer line designation, such as K for a line at 393.366 nm emerging from singly-ionized Ca+, though some of the Fraunhofer "lines" are blends of multiple lines from several different species. Other photons will have the right energies to raise electrons from the second to the fourth orbit, or from the first to the fifth orbit, and so on. This can be done, for instance, by causing the atoms to undergo collisions.