Laporte Selection Rule in Quantum Mechanics
38 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What does the Laporte selection rule state?

Only allowed transitions are those occurring with a change in parity or a change in the azimuthal quantum number by ±1.

Which of the following transitions is allowed according to the Laporte selection rule?

  • gerade to ungerade
  • ungerade to gerade
  • gerade to gerade
  • Both A and B (correct)

    • The Laporte selection rule applies to tetrahedral complexes.

    False

    What does the Spin Selection rule state?

    <p>Transitions that involve a change in spin multiplicity are forbidden, and any transition for which ∆S = 0 is allowed.</p> Signup and view all the answers

    Which of the following mechanisms can allow 'forbidden' transitions to become somewhat 'allowed'?

    <p>All of the above</p> Signup and view all the answers

    What happens to the center of symmetry during Vibronic Coupling?

    <p>There can be a temporary/transient loss of the center of symmetry.</p> Signup and view all the answers

    How do tetrahedral complexes affect color transitions?

    <p>They tend to be more intense in color due to the lack of a center of symmetry, which largely overcomes the Laporte selection rules.</p> Signup and view all the answers

    [Co(H2O)6]2+ is a type of _____ complex.

    <p>octahedral</p> Signup and view all the answers

    [CoCl4]2- exhibits a _____ color.

    <p>intense blue</p> Signup and view all the answers

    What is a characteristic of transitions that are allowed according to the Laporte selection rule?

    <p>They involve a change from gerade to ungerade orbitals.</p> Signup and view all the answers

    In terms of the azimuthal quantum number, what does the Laporte selection rule permit?

    <p>A change of ±1 only.</p> Signup and view all the answers

    Which type of complexes does the Laporte selection rule not apply to?

    <p>Tetrahedral complexes</p> Signup and view all the answers

    What is the restriction described by the Spin Selection rule?

    <p>Transitions that involve a change in spin multiplicity are forbidden.</p> Signup and view all the answers

    During an electronic transition, what must happen for the Laporte selection rule to apply?

    <p>There has to be a change in dipole moment.</p> Signup and view all the answers

    What is the resulting color of the tetrahedral complex [CoCl4]2-?

    <p>Intense blue</p> Signup and view all the answers

    What is the effect of the absence of a center of symmetry in tetrahedral complexes?

    <p>It helps overcome the Laporte selection rule.</p> Signup and view all the answers

    Which complex has a significantly higher transition intensity compared to [Co(H2O)6]2+?

    <p>[CoCl4]2-</p> Signup and view all the answers

    In which application has cobalt historically been used prior to 1400 BC?

    <p>Pottery glazes</p> Signup and view all the answers

    What characteristic of [Co(H2O)6]2+ leads to its relatively lower intensity in electronic transitions?

    <p>Presence of a center of symmetry</p> Signup and view all the answers

    Which factor contributes to the visibility of colors in tetrahedral complexes?

    <p>Absorption in visible light range</p> Signup and view all the answers

    What is the typical range of values for transition intensity in the tetrahedral complex [CoCl4]2-?

    <p>50 - 150 m²mol⁻¹</p> Signup and view all the answers

    What occurs if the absorption for an octahedral complex falls in the ultraviolet range?

    <p>Color is perceived differently than in visible light.</p> Signup and view all the answers

    What is fluorescence?

    <p>It is the emission of light with a longer wavelength and lower energy than the absorbed radiation.</p> Signup and view all the answers

    Which theory explains the colors of metal complexes?

    <p>Crystal Field Theory</p> Signup and view all the answers

    What is one major drawback of Crystal Field Theory?

    <p>It neglects covalent bonding in metal complexes.</p> Signup and view all the answers

    How are ligands classified in Crystal Field Theory?

    <p>Strong, intermediate, and weak.</p> Signup and view all the answers

    Which of the following complexes is expected to have the most intense color?

    <p>Fe4[Fe(CN)6]3</p> Signup and view all the answers

    Which selection rule is primarily violated in spin-forbidden transitions?

    <p>Spin selection rule</p> Signup and view all the answers

    Which mechanism is involved in the temporary loss of center of symmetry during molecular vibrations?

    <p>Vibronic coupling</p> Signup and view all the answers

    What characterizes the emission of light by fluorescent complexes when exposed to UV light?

    <p>Emission occurs at a longer wavelength and lower energy.</p> Signup and view all the answers

    What phenomenon is not explained well by Crystal Field Theory?

    <p>Covalent bonding characteristics</p> Signup and view all the answers

    What is a consequence of the mixing of states in electronic transitions?

    <p>It leads to a breakdown of symmetry properties.</p> Signup and view all the answers

    Why do tetrahedral metal complexes tend to be more intense in color?

    <p>They do not follow the Laporte selection rule strictly.</p> Signup and view all the answers

    How is the spin selection rule partially lifted in heavier transition metals?

    <p>Via spin-orbit coupling.</p> Signup and view all the answers

    What must occur for a transition with ΔS ≠ 0 to happen?

    <p>There must be vibronic coupling.</p> Signup and view all the answers

    Which statement about the ΔS value in electronic transitions is correct?

    <p>ΔS = 0 is an allowed transition.</p> Signup and view all the answers

    Which factor primarily impacts the allowedness of electronic transitions in tetrahedral complexes?

    <p>Absence of center of symmetry</p> Signup and view all the answers

    Which of the following orbitals is found in tetrahedral complexes that do not have 'g' symmetry?

    <p>eg</p> Signup and view all the answers

    Study Notes

    Laporte Selection Rule

    • Allowed transitions require a change in parity, indicative of a dipole moment change.
    • Azimuthal quantum number (l) can change by ±1 during electronic transitions (Δl = ±1).
    • Applies to transitions between gerade (g) and ungerade (u) orbitals; transitions within the same parity (g-g or u-u) are forbidden.
    • Affects octahedral and square planar complexes due to their center of symmetry; but not applicable to tetrahedral complexes as they lack this symmetry.
    • d→d transitions are forbidden according to Laporte's rule.

    Spin Selection Rule

    • States that transitions involving a change in spin multiplicity (ΔS) are forbidden; ΔS = 0 is allowed, while ΔS ≠ 0 is forbidden.
    • Prohibits an electron from changing its spin state during electronic transitions, thus maintaining the integrity of spin configurations.

    Relaxation of Selection Rules

    • Forbidden electronic transitions can gain intensity through three mechanisms:
      • Vibronic Coupling: Temporary loss of molecular symmetry during asymmetric vibrations can relax the Laporte rule.
      • Mixing of States: Orbitals of different symmetry can mix, allowing transitions that were initially forbidden to occur.
      • Spin-Orbit Coupling: The interaction between spin and orbital angular momentum can allow partial lifting of the spin selection rule, particularly in heavier transition metals.

    Spectra of Tetrahedral Metal Ions

    • Tetrahedral complexes lack a center of symmetry; thus, d-levels are represented as e and t2 without ‘g’ designations.
    • This absence of symmetry enables greater intensity of color, making tetrahedral complexes more vibrant.
    • Example: Cobalt(II) chloride [Co(H2O)6]2+ appears pale pink in solution, while [CoCl4]2- is intensely blue, demonstrating significant color differences.
    • Cobalt blue, used historically in pottery, remains a valuable pigment for various applications today.

    Spectra of Octahedral vs. Tetrahedral Complexes

    • The intense d-d bands observed in tetrahedral complexes like [CoCl4]2- are contrasted with octahedral configurations like [Co(H2O)6]2+, emphasizing the strong influence of geometry on electronic transitions and overall color intensity.

    Laporte Selection Rule

    • Only allowed transitions involve a change in parity or a variation in the azimuthal quantum number (Δl = ±1).
    • Allowed transitions: gerade (g) to ungerade (u) or vice versa.
    • Transitions that maintain symmetry or are the same (g to g or u to u) are forbidden.
    • Applies to octahedral and square planar complexes due to their center of symmetry; not applicable to tetrahedral complexes.
    • d→d transitions are generally forbidden by the Laporte selection rule, reflecting the need for a change in dipole moment.

    Spin Selection Rule

    • Transitions that change spin multiplicity are forbidden; ΔS = 0 is allowed, ΔS ≠ 0 is forbidden.
    • Electron spins must remain unchanged during electronic transitions.
    • Example: In d5 high spin complexes, ΔS = 0 (allowed) and ΔS = 1 (forbidden).

    Relaxation of Selection Rules

    • Mechanisms that enable ‘forbidden’ transitions to occur include:
      • Vibronic Coupling: Temporary loss of center of symmetry during unsymmetrical vibrations.
      • Mixing of States: Symmetry properties of neighboring states may mix, affecting transitions.
      • Spin-Orbit Coupling: Interaction between spin and orbital angular momentum allows some relaxation of spin rules.

    Tetrahedral vs Octahedral Complexes

    • Tetrahedral complexes lack a center of symmetry, so the Laporte rule is less restrictive, resulting in brighter colors.
    • Example: [Co(H2O)6]²⁺ is pale pink, while [CoCl4]²⁻ is intense blue.
    • Cobalt blue, with historical significance in pottery, increases color intensity in tetrahedral complexes.

    Electronic Transition Intensities

    • Classification of transition types includes:
      • Spin forbidden, Laporte forbidden: e.g., [Mn(H2O)6]²⁺ shows low intensity (0.1).
      • Spin allowed, Laporte forbidden: e.g., [Co(H2O)6]²⁺ shows moderate intensity (1-10).
      • Spin allowed, Laporte allowed: e.g., KMnO4 shows high intensity (1000-10^6).

    Charge Transfer Spectra

    • Charge transfer spectra require a molecular orbital framework, involving σ and π bonding.
    • Complexes can have varied absorption characteristics, especially in ultraviolet range.

    Fluorescence

    • Fluorescence occurs when a substance emits light post absorption of electromagnetic radiation, often with lower energy than absorbed.
    • Fluorescent behavior can be observed in UV-irradiated complexes leading to visible light emission.

    Crystal Field Theory (CFT)

    • Advantages:

      • Explains colors and magnetic properties of metal complexes.
      • Classifies ligands as strong or weak.
      • Accounts for shape distortion in some complexes.

    • Disadvantages:

      • Overlooks covalent bonding aspects and orbital overlap.
      • Cannot predict shapes of complexes without hybridization context.
      • Charge transfer spectra are inadequately explained within CFT.

    Problem Solving: Color Intensity Order

    • Arrange complexes by color intensity: Fe4[Fe(CN)6]3, [CoBr4]²⁻, [MnF6]⁴⁻.
    • Order reasoning:
      • Fe4[Fe(CN)6]3 - Spin Forbidden, Laporte Forbidden.
      • [CoBr4]²⁻ - Spin Allowed, Laporte Allowed (Tetrahedral).
      • [MnF6]⁴⁻ - Spin Allowed, Charge Transfer transition (high intensity).

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Laporte and Spin Selection Rules PDF
    Laporte and Spin Selection Rules (PDF)

    Description

    Explore the Laporte selection rule and its significance in electronic transitions. This quiz will cover the conditions under which allowed transitions occur, specifically focusing on changes in parity and the azimuthal quantum number. Test your knowledge on the interaction of light with molecules.

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser