Emission spectrum: what it is and how it is produced

In general, all objects that contain energy emit electromagnetic radiation. If we order this radiation by wavelength, we obtain the emission spectrum of this object.

In chemistry, the emission spectrum refers to the electromagnetic radiation emitted by an atom or a molecule when it passes from an excited energy state to a lower energy state.

Let’s see what exactly is the emission spectrum and how it is produced.

Emission spectrum: definition

Iron emission spectrum

o Emission spectrum It is defined as the set of wavelengths emitted by an atom found in state of excitation. By emitting electromagnetic radiation, the excited atom passes to a lower energy state.

Each element in the periodic table has a unique emission spectrum known as a spectral signature so that by analyzing the emission spectrum of a substance we can identify the elements that compose it.

This procedure is called emission spectroscopy and it is a very useful tool in many fields of science. For example, it is used in chemical analysis and in astronomy to study the elements a star contains.

How the emission spectrum is produced

By absorbing energy, the atom passes from the ground state to the excited state.

The electrons of an atom tend to be distributed in such a way that the energy of the atom is as low as possible. This state is the baseline state.

When an atom is given energy, for example heat, electrons absorb energy and rise to higher energy levels. The atom is in an excited state.

The different energy levels are quantified. The electron’s energy cannot go up or down continuously, but in jumps between quantum levels.

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The excited state is not a stable state for the atom. It will always tend towards the baseline state. When an electron returns to a lower energy level, a photon is released, that is, electromagnetic radiation is emitted that will form the emission spectrum.

The energy of the emitted photon is equal to the energy difference between the excited state and the ground state and is related to electromagnetic radiation by the following equation:

Where E is the energy of the photon, v the frequency is Planck’s constant.

Each electron in an atom can be in several excited states as it can move up one, two or more energy levels. For this reason, an atomic emission spectrum is composed of an infinity of wavelengths, but always determined by the quantum states through which the electrons pass.

As each element has its own emission spectrum and different from the other elements, by studying the emission spectrum of an object it is possible to know the elements that compose it.

Relationship with the absorption spectrum

Just as each element emits certain wavelengths, each element only absorbs certain wavelengths. The absorbed wavelengths form the absorption spectrum.

The absorption spectrum and the emission spectrum are complementary. The wavelengths that are absorbed when going up to the excited state are the same wavelengths that are emitted when going back to the ground state.

Hydrogen absorption and emission spectrum

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