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Chapter 8: Problem 12

Based on the number of peaks (one), the intensity of the peak, and your understanding of the shell model: a) Explain why it is not possible to determine if the "unknown" atom is \(\mathrm{H}\) or \(\mathrm{He}\) ? b) Explain why the "unknown" atom cannot be Li.

Short Answer

Expert verified
The 'unknown' atom could be either hydrogen or helium because both elements could produce one spectral line indicating a single electron transition. Since lithium should exhibit multiple spectral lines due to having more potential electron transitions, the 'unknown' atom cannot be lithium.

Step by step solution

01

Understanding Atomic Spectra and Shell Model

Atomic spectra are unique to each element. When an atom absorbs energy, its electrons move to a higher energy level. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a light wave which forms a line of a certain color in the spectrum. Therefore, each line in an atomic spectrum corresponds to one electronic transition. The Shell Model of atom suggests that electrons inhabit energy levels, or shells, around the atomic nucleus.
02

Reason why it's not possible to determine if the 'unknown' atom is H or He

Both hydrogen and helium have one spectral line or peak in their atomic spectra, which means both elements have one possible electron transition. Hydrogen has one electron and helium has two, but helium's electrons both inhabit the lowest energy level (n=1), thus they have only one transition that corresponds to a photon being emitted or absorbed. Therefore, based on the given information, it's impossible to discern whether the atom is hydrogen or helium. The peak intensity could depend on factors other than the atom's identity such as temperature or pressure.
03

Explaining why the 'unknown' atom cannot be Li

Lithium atoms, in their ground state, have three electrons: two in the first energy level (n=1) and one in the second level (n=2). This means that lithium's electron has multiple possible transitions (from 2 to 1, and vice versa), thus should exhibit at least two spectral lines or peaks. Therefore, the atom in question cannot be lithium as it only has one peak as per the information given.

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Most popular questions from this chapter

What determines the height (or intensity) of each peak in a photoelectron spectrum?

What determines the position of each peak (where along the horizontal axis the peak is positioned) in a photoelectron spectrum?

The peak due to the \(n=1\) shell is predicted to be at a much higher ionization energy than the \(n=2\) peak because the \(n=1\) shell is "significantly closer to the nucleus.' Why is the distance of the shell from the nucleus important in determining the corresponding peak position in the photoelectron spectrum?
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