Why does emission not appear to be continuous

Consider another spectrum as shown below: Emission spectrum of carbon Clearly, this is not a continuous spectrum; however, it still represents visible radiation that has been separated into its constituent colors. In the image above, the horizontal axis shows the energy or color of the light, the same as the spectrum above, the light is emitted only at particular "discrete" energies corresponding to the bright lines.

It turns out that each chemical element emits its own characteristic pattern. The one shown above characteristic of carbon. These type of spectra can be generated for many elements by vaporizing the element in a flame.

While the colors in the above representations of spectra are pretty, their usefulness is limited. On top of that, they would convey no information at all if it the observed radiation was outside the limits of the human eye. Scientists, then, tend to use a different representation which permits a more rigorous analysis. Consider the spectrum as shown below. The top spectrum shows a narrow segment of Sun's spectrum of ultraviolet UV light. This representation has been modeled after the visible spectra.

Remember that our eyes can't see ultraviolet light; however, as with the visible spectra shown above, the horizontal axis the x-axis shows the energy or "color" of the observed light. Because each element has characteristic emission and absorption spectra, scientists can use such spectra to analyze the composition of matter.

When an atom emits light, it decays to a lower energy state; when an atom absorbs light, it is excited to a higher energy state. If the light that emerges is passed through a prism, it forms a continuous spectrum with black lines corresponding to no light passing through the sample at , , , and nm. Any given element therefore has both a characteristic emission spectrum and a characteristic absorption spectrum, which are essentially complementary images. Emission and absorption spectra form the basis of spectroscopy , which uses spectra to provide information about the structure and the composition of a substance or an object.

In particular, astronomers use emission and absorption spectra to determine the composition of stars and interstellar matter. Superimposed on it, however, is a series of dark lines due primarily to the absorption of specific frequencies of light by cooler atoms in the outer atmosphere of the sun.

By comparing these lines with the spectra of elements measured on Earth, we now know that the sun contains large amounts of hydrogen, iron, and carbon, along with smaller amounts of other elements. During the solar eclipse of , the French astronomer Pierre Janssen — observed a set of lines that did not match those of any known element.

Alpha particles are helium nuclei. Alpha particles emitted by the radioactive uranium, pick up electrons from the rocks to form helium atoms. Similarly, the blue and yellow colors of certain street lights are caused, respectively, by mercury and sodium discharges.

In all these cases, an electrical discharge excites neutral atoms to a higher energy state, and light is emitted when the atoms decay to the ground state. In the case of sodium, the most intense emission lines are at nm, which produces an intense yellow light.

There is an intimate connection between the atomic structure of an atom and its spectral characteristics. Most light is polychromatic and contains light of many wavelengths.

Light that has only a single wavelength is monochromatic and is produced by devices called lasers, which use transitions between two atomic energy levels to produce light in a very narrow range of wavelengths. Atoms can also absorb light of certain energies, resulting in a transition from the ground state or a lower-energy excited state to a higher-energy excited state.

This produces an absorption spectrum , which has dark lines in the same position as the bright lines in the emission spectrum of an element. Atoms of individual elements emit light at only specific wavelengths, producing a line spectrum rather than the continuous spectrum of all wavelengths produced by a hot object. Niels Bohr explained the line spectrum of the hydrogen atom by assuming that the electron moved in circular orbits and that orbits with only certain radii were allowed.

Lines in the spectrum were due to transitions in which an electron moved from a higher-energy orbit with a larger radius to a lower-energy orbit with smaller radius. The orbit closest to the nucleus represented the ground state of the atom and was most stable; orbits farther away were higher-energy excited states.

Transitions from an excited state to a lower-energy state resulted in the emission of light with only a limited number of wavelengths. Modified by Joshua Halpern Howard University. A gas cloud on its own, without a light source behind it, produces a line emission spectrum. When a gas is cool, it absorbs the same wavelengths of light as it would emit when it is hot. This is called a line absorption spectrum.

Therefore, when this light passes through a gas, the gas atoms may absorb certain wavelengths to produce a line absorption spectrum. Due to the nature of quantum physics, electrons can absorb and emit only specific, discrete energies. Every element has a characteristic arrangement of electron orbitals and energies that dictates what color the emission lines will be.

While many of the things we perceive are dictated by classical, continuous mechanics, the atomic world is dictated by discontinuity and probability. The electrons in an atom exist at discrete energy levels with no middle ground.

If an electron is excited to a new energy level, it jumps up to that level instantaneously. When electrons return to lower energy levels, they release energy in quantized packets. You can contrast this with a fire that slowly burns out.

A burning fire emits energy continuously as it cools and eventually burns out. An electron, on the other hand, emits all of its energy instantaneously and jumps to a lower energy level without passing through a transitional state. Energy from light exists in packets called photons.