Study the following emission spectra: (KICA) helium: krypton: What do you notice about the number of lines in both spectra? Account for the difference using concepts from the quantum mechanical model of the atom: 3 marks)
The Correct Answer and Explanation is:
Answer:
The emission spectrum of helium shows fewer lines compared to krypton, which has a much more complex spectrum with many more lines. This difference can be explained using the quantum mechanical model of the atom.
Helium has only two electrons and fewer energy levels available for electronic transitions. Therefore, it produces fewer emission lines. In contrast, krypton is a much larger atom with 36 electrons, which occupy many more energy levels and sublevels. These electrons can undergo numerous possible transitions between energy states, resulting in a dense and complex spectrum with many more emission lines.
According to the quantum mechanical model, electrons exist in quantized energy levels. When an electron in an atom absorbs energy, it moves to a higher energy level (excited state). When it falls back to a lower energy level, it emits energy in the form of light. Each transition corresponds to a specific wavelength, creating an emission line. Since krypton has more electrons and energy level combinations, it has more possible transitions, producing a greater number of spectral lines.
Extended Explanation:
The quantum mechanical model of the atom describes electrons as existing in specific quantized energy levels, with transitions between these levels resulting in the absorption or emission of photons. These transitions are not arbitrary; they are governed by the allowed energy states within the atom, which are determined by the atom’s electron configuration and the principles of quantum mechanics, such as the Pauli exclusion principle and Hund’s rule.
Helium, with just two electrons, has a relatively simple electron configuration: 1s². The number of allowed transitions between energy levels is limited because there are fewer electrons and fewer occupied orbitals. As a result, helium’s emission spectrum consists of fewer spectral lines, mostly in the ultraviolet and visible range.
In contrast, krypton is a noble gas with the electron configuration [Ar] 3d¹⁰ 4s² 4p⁶. With 36 electrons distributed across multiple shells and subshells, there are many more possible electronic transitions. Each of these transitions can result in the emission of a photon with a distinct wavelength, contributing to the densely packed and colorful emission spectrum seen for krypton.
Additionally, in heavier atoms like krypton, electron-electron interactions and sublevel splitting (such as fine and hyperfine structure) further increase the number of possible energy transitions. This complexity leads to a richer and more detailed spectrum.
Therefore, the observed difference in the number of lines between helium and krypton directly reflects the complexity of their atomic structures and supports the predictions of the quantum mechanical model.
