Emission and Absorption Spectra

An element is composed of a specific number of protons, the nuclear core of an atom, and its properties are determined by the number of electrons orbiting the nucleus. These electrons are positioned in specific energy levels called shells or orbitals that surround the nucleus in a pattern that corresponds to their energies. An atom in an element has a central core called a nucleus and a cloud of electrons around the nucleus. According to modern atomic theory, these electrons are arranged in energy levels, specifically called shells or orbitals, where their energies are quantized.

The shell which is closer to the nucleus has the lowest Energy compared to others. When energy is given to an atom externally, it makes the electrons move from one shell to another. This Movement Causes the absorption and emission Spectrum. Spectra may be divided into two classes according to the manner in which light interacts with the atoms of a gas or a liquid. These are emission and absorption spectra. The first one has a prominent feature that is dark lines produced due to absorption between two bright lines. Emission spectra will consist of bright lines formed when the atoms jump from a higher shell to a lower one while they emit energy during the process. This means that there must be an energy source like burning a substance or heating it intensely to generate emission spectra. 

Absorption Spectrum

The highlight of absorption spectra is that it shows dark lines on the spectrum. The light source, such as a light bulb or fluorescent tube, is used to produce electromagnetic radiation of all wavelengths. The beam of light is passed through the vapor of an element. When the element is cold, there will be no absorption of radiation, and so one gets an emission spectrum.

The energy of the given Photon is E = hc / λ

Where, E – the energy of the photon (Jmol-1)

c – Speed of radiation (ms-1)

h – Planck’s constant (Js)

λ – Wavelength (m) 

Absorption and emission spectra are the manifestations of atomic transitions. This is because light can be absorbed only when it makes an electron jump to a higher energy level. Thus, the absorption spectrum is obtained when electrons are made to jump from a lower energy level to higher levels. The reverse is true in the case of emission spectra; light emitted by atoms is produced as electrons drop down from a higher energy level to a lower one. Therefore, given the two types of spectra, absorption spectra correspond to an increase in kinetic energy (of electrons), whereas emission spectra correspond to a decrease in kinetic energy (of electrons).

The absorption spectrum can be defined as a spectrum of the spectral lines resulting from the absorption of electromagnetic radiation. When a material is exposed to the spectrum, some part of it may absorb energy when photons fall on the electrons in various atoms or molecules, raising them to higher energy levels or exciting them. The electrons return to their original states, releasing their energy. These energies are released as photons. Absorption lines are usually close together to their corresponding emitters and are broadened due to the thermal motion of the emitting species. They may also be shifted slightly from their corresponding emission wavelengths due to factors such as Doppler-shift.

Emission Spectrum

The emission spectrum of an atom or molecule is the set of wavelengths emitted by the atom as it transitions electron(s) from an excited state to a lower energy level.

The emission spectrum, on the other hand, is a spectrum of the amount of electromagnetic radiation emitted from a certain object. The intensity or brightness of an emission line depends on the transition rate between unstable and stable states, which in turn depends on the type of change in energy.

The emission spectrum consists of a continuous band of colours. The continuous band of colours means that there are no gaps in the spectrum. Each colour, as well as each wavelength, is emitted by an atom. The absorption spectra can be defined as the spectrum of electromagnetic radiation which passes through a medium after being absorbed. In order to absorb energy, the medium must have electrons which can move to higher energy levels when they become excited by absorbing a photon.

Emission and Absorption Spectrum: Difference

Here we are going to discuss the important feature of both the spectrum below

1. Emission spectra are produced when excited electrons are returned to a lower energy level. It is essentially a form of light. Absorption spectra, on the other hand, occur when energy is absorbed by an atom, and the electrons are raised to a higher energy level. The atom absorbs a photon of specific energy, and that photon’s light is then emitted at that same frequency.
2. Emission spectra are different from absorption spectra in several ways. Emission spectra show the wavelengths that are emitted by an atom, gas, or molecule. In contrast, absorption spectra result when a substance absorbs some wavelengths and emits others. Absorption is the opposite process to emission, wherein emission energy is released, while in absorption, energy is absorbed. When an object’s temperature rises above absolute zero (-273 degrees C), atoms and molecules have more energy to move around, vibrate and spin faster.

This extra energy excites electrons into higher orbitals, so they are no longer in the lowest energy state (known as the ground state). This can happen in many atoms and molecules because there are often multiple possible lowest energy states (electronic levels). When an electron loses its extra energy, it falls down to its original orbital around the nucleus, releasing a photon of electromagnetic radiation (light). Emission spectra always use photons of light as the source of excitation for leaving an excited state. Excitation can also occur by applying a voltage across a gas-filled tube or applying heat to a solid sample.

Conclusion

To draw the difference between emission and absorption spectra, first of all, we should know what both spectra are. The emission spectrum is a collection of different wavelengths of electromagnetic radiation emitted by a substance. While absorption is the opposite of emission, the electromagnetic radiation absorbed by the substance determines the absorption spectrum. The simple difference between emission and absorption spectra is to do with the creation or destruction of photons, respectively.