Hydrogen, Atom and Spectrum: Emission & Absorption Explained

The fundamental understanding of the behavior of light and matter behavior depends on studying spectral lines. The spectral lines found in the spectrum reveal important details about the composition and temperature characteristics as well as other physical properties of the substances.  In physics and chemistry, spectral lines are vital tools for studying the atomic and molecular structure of matter. This article explores spectral lines and their process of formation and scientific importance.

What Are Spectral Lines?

Spectral lines are dark or bright lines that appear in the spectrum of light emitted or absorbed by substances. Light passing through materials including gases or exposed to heat causes atoms and molecules to absorb or emit light energy at specific wavelengths. These wavelengths correspond to distinct energies of light and form a series of lines, each representing a transition between energy levels within an atom or molecule.

There are two primary types of spectral lines:

1. Absorption Lines: These are dark lines that appear in the spectrum of light after it has passed through a gas or another substance. When light of specific wavelengths interacts with the atoms in the substance, it is absorbed. These wavelengths are then missing from the spectrum, creating the absorption lines.
    
2. Emission Lines: These are bright lines emitted by atoms or molecules when electrons jump from a higher to a lower energy state. The energy difference between these states corresponds to a specific wavelength of light, resulting in a line on the emission spectrum.

Types of Spectra

Spectral lines can be observed in three primary types of spectra:

1. Continuous Spectrum: This is a spectrum that contains all the wavelengths of light in a given range, with no gaps. It is produced by solid, liquid, or densely packed gases, like the spectrum of sunlight. A continuous spectrum does not contain spectral lines.
    
2. Emission Spectrum: This spectrum consists of bright lines at specific wavelengths corresponding to the light emitted by excited atoms or molecules. Each line represents a particular transition between energy levels in the atom.
    
3. Absorption Spectrum: When light passes through a cooler gas or substance, it creates an absorption spectrum, which contains dark lines at specific wavelengths where light has been absorbed by atoms in the substance.

Let's have a look at the most important sure-shot question from spectral lines for NEET 2025

Question 1:

The wave number of the spectral line in the emission spectrum of hydrogen will be equal to 8/9 times the Rydberg constant if the electron jumps from

1. n=3 to n=1
2. n=10 to n=1
3. n=9 to n=1
4. n=2 to n=1

Correct answer is A.

Question 2:

How many spectral lines will be possible?

1. 1
2. 2
3. 3
4. 4

Correct answer is: C

NOTE: Questions of these types should be practiced a lot by the NEET 2025 aspirants. Students should solve problems focusing on the number of spectral lines, number of spectrums, wave number, rydberg’s equation, the initial and final level from which the electron jumps. 
 

FAQs 

1. What is the difference between emission and absorption spectral lines?

Emission spectral lines are bright lines in the spectrum emitted when electrons fall to lower energy levels within an atom. Absorption spectral lines are dark lines that appear when atoms absorb specific wavelengths of light, preventing those wavelengths from reaching the observer.

2. Can spectral lines tell us about the speed of an object?

Yes, spectral lines can be used to measure the speed of an object. If the lines are shifted toward the red end of the spectrum, the object is moving away. If the lines are shifted toward the blue end, the object is moving toward the observer.

3. Why do different elements have different spectral lines?

Each element has a unique arrangement of electrons and energy levels. When electrons transition between these levels, they emit or absorb light at specific wavelengths. These wavelengths are unique to each element, creating distinct spectral lines for each one.

Conclusion

Spectral lines provide a window into the microscopic world of atoms and molecules. From identifying elements to measuring the temperature and motion of celestial bodies, they play a crucial role in modern science. Their study, whether in a laboratory or through a telescope, helps scientists unlock the secrets of the universe, making them one of the most valuable tools in physics and chemistry.