Ch.8 - The Quantum-Mechanical Model of the Atom

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.8 - The Quantum-Mechanical Model of the Atom

Problem 74

Chapter 8, Problem 74

According to the quantum-mechanical model for the hydrogen atom, which electron transition produces light with the longer wavelength: 3p → 2s or 4p → 3p?

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Understand that the wavelength of light emitted during an electron transition is inversely proportional to the energy difference between the two levels. This means that a smaller energy difference results in a longer wavelength.

Recall the formula for the energy difference between two levels in a hydrogen atom: \( \Delta E = -13.6 \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right) \) eV, where \( n_i \) and \( n_f \) are the initial and final principal quantum numbers, respectively.

For the transition 3p \( \rightarrow \) 2s, identify the principal quantum numbers: \( n_i = 3 \) and \( n_f = 2 \).

For the transition 4p \( \rightarrow \) 3p, identify the principal quantum numbers: \( n_i = 4 \) and \( n_f = 3 \).

Compare the energy differences for both transitions using the formula, and determine which transition has the smaller energy difference, indicating the longer wavelength of emitted light.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron Transitions

Electron transitions refer to the movement of electrons between different energy levels or orbitals in an atom. When an electron moves from a higher energy level to a lower one, it releases energy in the form of light. The energy of the emitted light corresponds to the difference in energy between the two levels, influencing the wavelength of the light produced.

Wavelength and Energy Relationship

The wavelength of light is inversely related to its energy, as described by the equation E = hc/λ, where E is energy, h is Planck's constant, c is the speed of light, and λ is wavelength. This means that transitions resulting in lower energy emissions will produce longer wavelengths of light. Understanding this relationship is crucial for determining which electron transition produces light of a longer wavelength.

Quantum Numbers and Energy Levels

Quantum numbers describe the properties of atomic orbitals and the electrons in those orbitals. The principal quantum number (n) indicates the energy level, while the angular momentum quantum number (l) indicates the shape of the orbital. In the hydrogen atom, transitions between different principal quantum levels (like 2s to 3p or 3p to 4p) determine the energy and wavelength of the emitted light, with higher n values generally corresponding to higher energy levels.

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Principal Quantum Number

Related Practice

Textbook Question

Determine whether each transition in the hydrogen atom corresponds to absorption or emission of energy. a. n = 3 → n = 1 b. n = 2 → n = 4 c. n = 4 → n = 3

The human eye contains a molecule called 11-cis-retinal that changes shape when struck with light of sufficient energy. The change in shape triggers a series of events that results in an electrical signal being sent to the brain that results in vision. The minimum energy required to change the conformation of 11-cis-retinal within the eye is about 164 kJ/mol. Calculate the longest wavelength visible to the human eye.

An electron in the n = 7 level of the hydrogen atom relaxes to a lower-energy level, emitting light of 397 nm. What is the value of n for the level to which the electron relaxed?

Calculate the frequency of the light emitted when an electron in a hydrogen atom makes each transition: a. n = 4 → n = 3 b. n = 5 → n = 1 c. n = 5 → n = 4 d. n = 6 → n = 5

Sketch the 1s and 2p orbitals. How do the 2s and 3p orbitals differ from the 1s and 2p orbitals?

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