Hydrogen Spectrum Definition

Hydrogen is the very first element of Henry Moseley’s modern periodic table. It is non-metal and consists of one electron and one proton. Every element in the periodic table has its properties, one of them being the emission of electromagnetic radiation. Whenever the electron of a hydrogen atom absorbs energy or radiation, it is called the excited electron, and the state is known as the excited state. Due to natural reasons, this electron is bound to lose energy and come back to its normal state, which is a stable state. During this process, the hydrogen atom’s electron emits EM radiation called the spectrum, which is a line spectrum. Let’s understand why and how it radiates energy.

Hydrogen spectrum and its explanation

In an experiment in which an electric discharge of high voltage is made to pass through a gaseous hydrogen molecule, the hydrogen molecules dissociate. The H atoms get excited by this high power and possess an energy that emits electromagnetic radiation of discrete frequencies. The spectrum of hydrogen thus consists of several series of lines named after the scientists who discovered them; for example, the Lyman series, the Pfund series, and many more. The quantised electronic structure of an atom is perfectly illustrated by the hydrogen spectrum and helps us understand it better. 

Hydrogen spectrum wavelength

The electrons transit from lower energy levels to higher energy levels when the hydrogen atom absorbs photons say n = 1 to n = 2. The electron loses the photon and jumps back to lower energy levels to stabilise the atom again, say n = 2 to n = 1. This photon belongs to some wavelength, and the amount of energy radiated depends on the energy levels, which makes the wavelength different for different transitions. For example: when the electron jumps from n = 4 to n = 1, the wavelength corresponding to it is 97 nm. This is known as hydrogen spectrum wavelength. 

In his observation, Rydberg concluded that the series of lines in the hydrogen spectrum could be described as an equation determining the wavenumber. The first five of these series are named Lyman, Balmer, Paschen, Brackett, and Pfund, out of which only Balmer belongs to the visible region in the electromagnetic spectrum. Lyman belongs to UV. Paschen, Brackett and Pfund belong to the IR region.

All this all comes from the Bohr’s model of the hydrogen atom, which provided two postulates:

1. There are circular paths called the orbits around the nucleus in which the electron moves.
2. Time is not the factor determining the energy of an electron that revolves in these orbits.

So the explanation of the line spectrum comes from Bohr’s model of the hydrogen atom, which states that the energy is absorbed when an electron moves from the orbit of a lower quantum number to a higher quantum number, and energy is emitted when an electron moves from orbit of a higher quantum number to lower quantum number. And this energy gap between the two orbits is Efinal – Einitial. This study of emission and absorption spectra is called spectroscopy.

Experiment with the hydrogen spectrum

Start with a glass tube with hydrogen gas and connect it with a high power supply. By turning on the power, we supply the energy to the atom, thus making the electron excited—the electron moves to the outer energy level, which can be measured by spectroscopy. We will also require a collimator, and the telescope and the axis of both should intersect the vertical axis through the spectroscope. Using the equation that Rydberg gave for the wavenumber and the equation 𝒅𝒔𝒊𝒏𝜽 = 𝒎 and by observing the experiment, we can find that the Rydberg constant is 1,09,73,731.568160 per metre.

Another experiment can also be performed: take a hydrogen discharge tube; a hydrogen-containing slim tube at low pressure with an electrode at each end. When a high voltage is supplied, the tube lights up bright pink. If this light is passed through a prism, it splits into various colours.

Excitation of the electron

When the electron absorbs energy, it is excited to higher quantum numbers. Still, there are two possibilities: either it completely leaves the atom if the energy is way too much, or it can come back to its normal state after some time. This electron jumping from a high level to a lower level can be achieved in two ways: either it can jump directly to n = 1, or it can be done in steps. If the electron is excited to a level above 2, first it can come to n = 2 and then n = 1.

Conclusion

In this article, we learned about hydrogen and the hydrogen spectrum. Bohr’s contribution to the structure of an atom helped to understand the absorption and emission spectrum. Excitation of electrons to higher state and then the emission of energy while jumping back to lower state and this energy has a series of a line which correspond to different orbits and the name of spectra according to the scientists who discovered them(Lyman, Balmer, Paschen, Brackett and Pfund). Wavelength was also discussed, and also the wavenumber equation by observation of Rydberg. Experiment which proves Rydberg constant and fun experiment demonstrating the emission spectrum. The primary importance of the hydrogen spectrum is that it shows the quantised electronic structure of an atom.