Understanding Spectra
A spectrum (plural: spectra) could be a range of bands of colours that appear when light passes through a prism or water drops. The simplest example of a spectrum could be a rainbow. There are 3 kinds of atomic spectra and they are emission spectra, absorption spectra, and continuous spectra. Each spectrum holds a large variety of data. For example, there are many alternative mechanisms by which an object, such as a star, can produce light. Features of those mechanisms incorporate a characteristic spectrum.
Spectroscopy is very useful in helping scientists understand how an object like a black hole, star, or active galaxy produces light, how fast it's moving, and what components it's composed of.
What is Spectrum?
The distinctive electromagnetic radiation wavelengths that are released or absorbed by an object or substance, atom, or molecule are known as the spectrum.
Nature makes a stunning spectrum we tend to call rainbows. Sunlight passing through raindrops is spread out to display its varied colours, the different colours are simply the way our eyes perceive radiation with slightly different energies.
A spectrum is just a chart or a graph that shows the intensity of light being emitted over a range of energies. It ranges from the longest radio waves to the shortest X-rays and gamma rays. These invisible waves enable us to make calls from our mobile devices, use the internet, call a cab, pull up directions to a destination, and do everything on our mobile devices. Thus, the frequencies we tend to use for wireless communication are also a part of the electromagnetic spectrum.
Emission Spectra
Types of Spectrum
An instrument designed for visual observation of spectra is named a spectroscope and the photographs are a spectrograph. Spectra are also classified according to the character of their origin—i.e., emission or absorption.
Some of the spectra are listed below :
Electromagnetic spectrum
Emission spectrum
Continuous spectra
Discontinuous spectra
Absorption spectrum
Electromagnetic Spectrum: The electromagnetic (EM) spectrum is the range of all kinds of EM radiation. The visible radiation from a lamp to the rays used to figure out a fractured bone, all are electromagnetic radiation. Also, the series of these totally different radiations is named the electromagnetic spectrum.
Electromagnetic Spectrum
Emission Spectra: The spectrum obtained by the radiation emitted by a substance that has absorbed energy is named emission spectra. There are 2 kinds of emission spectrum: continuous spectrum and discontinuous spectrum.
Continuous Spectrum: This spectrum contains all wavelengths of light in a bound range. Hot, dense light sources like stars, as an example, emit an almost continuous spectrum of light that travels out in all directions and interacts with different materials in space. The broad range of colours that a star emits depends on its temperature.
Discontinuous Spectrum: A discontinuous spectrum may be a type that contains gaps, holes, or breaks in terms of the wavelengths that it contains. Depending on the type of lines obtained, a discontinuous spectrum will be categorised into the following:
Line spectra or atomic spectra
Band spectra or molecular spectra
Continuous Spectrum
Absorption Spectrum: It is formed by electromagnetic radiation that has passed through a medium in which radiation of specific frequencies is absorbed. In an absorption spectrum, parts of a continuous spectrum seem like dark lines or gaps. These dark lines indicate that the wavelengths are absorbed by the medium through which the light has passed. An absorption spectrum shows us which wavelengths of light were absorbed by a specific gas. It's like a continuous spectrum, or rainbow, with some black lines.
Line Spectrum
An electron in the excited state when making the transition to lower energy states, the light of fixed wavelengths is emitted. These emitted wavelengths seem as sharp bright lines within the dark background forming a spectrum. This is often called the line emission or discontinuous spectrum. As electrons responsible for producing such a spectrum are a part of the atom, line spectra are also known as atomic spectra. Inert gases, metal vapours, and atomised non-metals form this type of spectra. The spectrum of the elements may be a “characteristic property” of the elements and is commonly termed as “fingerprints” of the elements.
Band Spectrum
This spectrum is given by hot metals and molecular non-metals. In this form of spectra discontinuity or gaps are seen between the bands or closely spaced bright lines. It's a characteristic property shown by molecules.
The key difference between continuous and line spectra is that the continuous spectrum contains all the wavelengths in a very given range whereas the line spectrum contains only a couple of wavelengths.
Uses of Spectrum
Electromagnetic Spectrum
Gamma Rays: These rays are used to sanitise medical instrumentation and inhibit the growth of microorganisms.
X-rays: These rays are used to visualise the inside of a body while not creating an incision. These rays are used for scanning functions.
Ultraviolet Light: These rays kill microbes, therefore are used extensively to disinfect instrumentation.
Visible Light: These rays facilitate us to visualise things around us.
Infrared ays: As these rays will simply penetrate the skin, they are used widely in cosmetic applications. It's used in remote controls, electrical hearts, and thermal cameras.
Microwave: It is widely used in microwave ovens to transmit the thermal energy required to cook food. Additionally used to guide aeroplanes.
Radio Waves are used in radio and television broadcasts.
Moreover, atomic absorption spectroscopic analysis is used for deciding the atomic structure of a sample, characterization of macromolecules, space exploration, and many more.
Interesting Facts
A human eye can see a wavelength that ranges between 390 to 700 nm.
The wavelength of light varies by its type.
Our eyes acknowledge each wavelength by a distinct colour. Red colour has the longest and violet has the shortest wavelength.
Cones in human eyes work as a receiver for these tiny visible light waves.
Some other creatures can see components of the spectrum that aren't visible to us. For instance, some insects can see UV light.
Important Question
1. Name the objective property of a given colour once it undergoes refraction.
a) Frequency
b) refractive index
c) Wavelength
d) velocity
Ans: (c) Frequency
2. Name electromagnetic waves which will go through a quartz prism.
a) UV rays
b) Gamma rays
c) visible light
d) Infrared rays
Ans: (a) UV rays
Conclusion
From this article, we are able to conclude that we are continuously under the impact of electromagnetic radiation. From warming ourselves under the sun throughout winter to tuning our radio, to watching TV, sending a text message, or popping popcorn in a microwave, we are using electromagnetic energy. We rely on this energy each hour of each day. Without it, the world we all know couldn't exist at all.
FAQs on Spectrum
1. What is a spectrum in the context of Chemistry?
In Chemistry, a spectrum refers to the unique pattern of electromagnetic radiation that is either emitted or absorbed by a substance. When light or any form of energy passes through a substance, atoms or molecules can absorb energy and jump to a higher energy state, or emit energy as they fall to a lower state. This pattern, when plotted as a graph of intensity versus wavelength or frequency, is called a spectrum. A simple example is the rainbow, which is the visible light spectrum of the sun.
2. What is the key difference between an emission spectrum and an absorption spectrum?
The key difference lies in how they are formed and what they look like. An emission spectrum is produced when a substance emits light or radiation after being energised. It appears as a series of bright lines or bands on a dark background. In contrast, an absorption spectrum is formed when continuous radiation passes through a substance, which absorbs specific wavelengths. It appears as a continuous spectrum (like a rainbow) with dark lines or gaps at the wavelengths that were absorbed.
3. How are continuous and line spectra produced?
The origin of these spectra differs based on the source of light:
- A continuous spectrum is produced by a source that emits light of all possible wavelengths in a given range. Hot, dense objects like the filament of an incandescent bulb or a star's core are common sources of continuous spectra.
- A line spectrum, also known as an atomic spectrum, is produced by excited atoms in a gaseous state. When electrons in these atoms transition from a higher energy level to a lower one, they emit light at very specific, discrete wavelengths, creating a pattern of sharp, distinct lines.
4. Why is the line spectrum of an element often called its 'fingerprint'?
A line spectrum is called an element's 'fingerprint' because it is unique to that specific element. Every element has a distinct arrangement of electrons and energy levels. Consequently, when its atoms are excited, they emit light at a set of wavelengths that no other element produces. Just as a fingerprint can uniquely identify a person, this characteristic pattern of spectral lines allows scientists to identify the presence of a specific element in any sample, whether in a lab or a distant star.
5. What is the significance of the different series (Lyman, Balmer, Paschen) in the hydrogen spectrum?
The different series in the hydrogen spectrum correspond to electron transitions ending at different principal energy levels. Their significance lies in categorising the emitted radiation:
- The Lyman series corresponds to transitions ending at the ground state (n=1) and its lines are found in the ultraviolet (UV) region.
- The Balmer series involves transitions ending at the first excited state (n=2). These lines are primarily in the visible region of the electromagnetic spectrum.
- The Paschen series consists of lines from transitions ending at the second excited state (n=3), and these are found in the infrared (IR) region.
6. What are some important real-world applications of spectroscopy?
Spectroscopy has numerous important applications across various fields. For example, in astronomy, it helps determine the chemical composition, temperature, and motion of distant stars and galaxies. In chemistry, it's used for identifying unknown substances and determining molecular structures. In medicine, specific types of spectroscopy like MRI (a form of radio wave spectroscopy) are used for diagnostics. Everyday technology also uses the electromagnetic spectrum, from microwaves in ovens to radio waves for communication.
7. Why does an absorption spectrum appear as dark lines against a continuous background?
An absorption spectrum's dark lines appear because a cool, less dense gas is placed between a source of continuous light (like a star) and the observer. As the continuous spectrum of light passes through the gas, the atoms in the gas absorb photons of very specific energies (and thus specific wavelengths) that match the energy required to excite their electrons to higher levels. These specific wavelengths are removed from the continuous spectrum, so when we view the light, those 'missing' wavelengths appear as dark lines or gaps.
