The key difference between hydrogen and helium emission spectra is that the helium emission spectrum (plu. spectra) has more lines than that of the hydrogen emission spectrum (plu. spectra).
The emission spectrum of a chemical element or compound is the series of lines that represent the wavelengths of electromagnetic radiation emitted by that chemical element while the transition of an electron from a high energy level to a low energy level.
CONTENTS
1. Overview and Key Difference
2. What is Hydrogen Emission Spectra
3. What is Helium Emission Spectra
4. Side by Side Comparison – Hydrogen vs Helium Emission Spectra in Tabular Form
5. Summary
What is Hydrogen Emission Spectra?
The hydrogen emission spectrum is a spectrum produced by the emission of light by hydrogen atoms in excited states. There, when we pass a beam of white light through a sample of hydrogen gas, then the atoms absorb energy. After that, the electron in the hydrogen atom gets excited to a higher energy level. However, since residing in a high energy level is unstable, these electrons tend to come back to the ground level (energy level at which they existed previously) emitting a photon as electromagnetic radiation that has an energy equal to the energy difference between these higher and lower energy levels.
Figure 01: Hydrogen Emission Spectrum
Moreover, the amount of energy at each energy level is a fixed value. Therefore, the transition will always produce a photon with the same energy. We can observe the emission spectrum as coloured light on a black background. However, the number of lines we can observe here is less than that of the helium emission spectrum.
What is Helium Emission Spectra?
The helium emission spectrum is a spectrum produced by the emission of light by helium atoms in excited states. It has more lines in it compared to hydrogen emission spectrum. It is mainly because the helium atom has more electrons than a hydrogen atom. Therefore, more electrons get excited when we pass a white light beam through a helium sample, and it causes the emission of more spectral lines.
Figure 02: Helium Emission Spectrum
Unlike in hydrogen, there are electron-electron repulsions and different nuclei-electron attractions in the helium atom. Therefore, different spectra (different from hydrogen) comes out with different wavelengths for the helium atom.
What is the Difference Between Hydrogen and Helium Emission Spectra?
The hydrogen emission spectrum is a spectrum produced by the emission of light by hydrogen atoms in excited states. On the other hand, the helium emission spectrum is a spectrum produced by the emission of light by helium atoms in excited states. And, the key difference between hydrogen and helium emission spectra is that the helium emission spectrum has more lines than that of the hydrogen emission spectrum. It is mainly because hydrogen has one electron per atom while helium has two electrons per atom.
Furthermore, a significant difference between hydrogen and helium emission spectra is that there is no effect from electron-electron repulsions on hydrogen emission spectra due to the presence of a single electron in hydrogen atom whereas electron-electron repulsions affect the helium emission spectra due to the presence of two electrons.
Summary – Hydrogen vs Helium Emission Spectra
The emission spectrum is a spectrum that shows a series of lines on a black background. Here, the emission of light by hydrogen atoms in excited states produces the hydrogen emission spectrum. Whereas, the emission of light by helium atoms in excited states produces the helium emission spectrum. The key difference between hydrogen and helium emission spectra is that the helium emission spectrum has more lines than that of the hydrogen emission spectrum.
Reference:
1. Libretexts. “6.3: Line Spectra and the Bohr Model.” Chemistry LibreTexts, National Science Foundation, 26 Nov. 2018. Available here
2. “Hydrogen Spectral Series.” Wikipedia, Wikimedia Foundation, 4 Nov. 2018. Available here
Image Courtesy:
1.”Bright-line Spectrum-Hydrogen”By Patrick Edwin Moran – Own work, (CC BY-SA 3.0) via Commons Wikimedia
2.”Helium Emission Spectrum”By Jkasd – Own work using data from NIST., (CC BY 3.0) via Commons Wikimedia