A spectral line is prefer a fingerprint that have the right to be used to identify the atoms, elements or molecules present in a star, galaxy or cloud of interstellar gas. If we separate the incoming light from a celestial source using a prism, we will certainly often check out a spectrum of colours crossed via discrete lines. Keep in mind that spectral lines deserve to also happen in various other areas of the electromagnetic spectrum, although we can no much longer use a prism to assist recognize them.

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There are 2 forms of spectral lines in the visible part of the electromagnetic spectrum:


Emission lines are viewed as coloured lines on a black background.

Absorption lines are seen as black lines on a coloured background.

The visibility of spectral lines is described by quantum mechanics in terms of the power levels of atoms, ions and molecules. These energy levels depend on the numbers of protons, electrons and neutrons in an atom, and the restricted set of configurations in which these elepsychological particles have the right to exist (the collection of quantum numbers). Atoms prefer to be in their ground state, wright here every one of the electrons are situated as cshed to the nucleus as possible. Absorption lines take place as soon as an atom, facet or molecule absorbs a photon through an energy equal to the distinction in between two energy levels. This causes an electron to be advocated into a higher energy level, and also the atom, aspect or molecule is said to be in an excited state. Emission lines happen once the electrons of an excited atom, aspect or molecule relocate between power levels, returning in the direction of the ground state.

The spectral lines of a specific element or molecule at remainder in a laboratory constantly take place at the same wavelengths. For this factor, we are able to determine which facet or molecule is causing the spectral lines. If the emitter or absorber is in activity, however, the place of the spectral lines will be Doppler shifted along the spectrum. A redshift (spectral lines move to much longer wavelengths) occurs for an emitter/absorber moving ameans from the observer, while a bluetransition (spectral lines move to shorter wavelengths) corresponds to motion in the direction of the observer.

Spectral lines might likewise be broadended by:

Collisional Broadening: because of interactions through adjoining atoms, ions or moleculesZeeguy Splitting: wright here power levels are split right into sub-levels by a magnetic field.

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The Hesitation Principle also gives a organic broadening of all spectral lines, via a herbal width of Δν = ΔE/h ≈ 1/Δt wright here h is Planck’s continuous, Δν is the width of the line, ΔE is the corresponding spreview in energy, and t is the life time of the power state (frequently ~10-8 seconds).