Electronic Spectroscopy: UV and Visible Absorption
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Questions and Answers

Which of the following events occurs when a molecule transitions from a higher energy level to a lower energy level?

  • Emission of radiation (correct)
  • Excitation
  • Absorption of radiation
  • Nonradiative decay
  • What is the primary cause of electronic excitation in a molecule?

  • Absorption of radio waves
  • Absorption of UV-vis photons (correct)
  • Absorption of microwave radiation
  • Absorption of infrared radiation
  • What is the name of the molecular orbital that an electron is typically promoted from during electronic excitation?

  • Pi antibonding orbital
  • LUMO
  • HOMO (correct)
  • Sigma bonding orbital
  • What is the name of the group of atoms in a molecule that absorbs light, whether or not a color is produced?

    <p>Chromophore (C)</p> Signup and view all the answers

    What is the term used to describe a transition from a higher energy level to a lower energy level without the emission of radiation?

    <p>Nonradiative decay (C)</p> Signup and view all the answers

    Which region of the electromagnetic spectrum is associated with electronic excitation of molecules?

    <p>Ultraviolet and visible (A)</p> Signup and view all the answers

    What is the primary requirement for a molecule to exhibit an electronic spectrum?

    <p>The molecule must have a chromophore (A)</p> Signup and view all the answers

    Which type of molecular orbital transition is typically involved in electronic excitation?

    <p>HOMO to LUMO (D)</p> Signup and view all the answers

    What is the primary energy range (in kJ/mol) associated with electronic excitation in molecules?

    <p>10^14 to 10^16 kJ/mol (B)</p> Signup and view all the answers

    What is the term used to describe the process of a molecule absorbing a photon of UV-visible light?

    <p>Absorption (A)</p> Signup and view all the answers

    What is the primary cause of the observed color in a molecule that absorbs visible light?

    <p>The molecule absorbs light of a specific wavelength (A)</p> Signup and view all the answers

    Which of the following transitions is not considered an electronic transition?

    <p>Vibrational transitions (D)</p> Signup and view all the answers

    Which of the following statements about electronic transitions is incorrect?

    <p>Electronic transitions are always accompanied by the emission of light (D)</p> Signup and view all the answers

    Which region of the electromagnetic spectrum has the highest energy associated with it?

    <p>Cosmic rays (A)</p> Signup and view all the answers

    Flashcards

    Emission of radiation

    The process where a molecule releases energy by transitioning from a higher energy level to a lower energy level, often resulting in the emission of light.

    UV-vis photon absorption

    The absorption of photons in the ultraviolet-visible (UV-Vis) region of the electromagnetic spectrum is the primary cause of electronic excitation in molecules.

    HOMO

    The highest occupied molecular orbital (HOMO) is the molecular orbital from which an electron is promoted during electronic excitation.

    Chromophore

    A chromophore is a group of atoms in a molecule that absorbs light, regardless of whether it produces a visible color.

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    Nonradiative decay

    Nonradiative decay refers to the transition of a molecule from a higher energy level to a lower energy level without the emission of radiation.

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    UV-Vis region

    Electronic excitation of molecules predominantly occurs in the ultraviolet and visible regions of the electromagnetic spectrum.

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    Chromophore requirement

    The presence of a chromophore is a prerequisite for a molecule to exhibit an electronic spectrum, as it is the chromophore that absorbs light.

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    HOMO-LUMO transition

    Electronic excitation typically involves the transition of an electron from the HOMO to the LUMO (lowest unoccupied molecular orbital).

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    Electronic excitation energy range

    Electronic excitation in molecules typically occurs in the energy range of 10^14 to 10^16 kJ/mol.

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    Absorption

    Absorption refers to the process where a molecule absorbs a photon of UV-visible light, causing an electron to transition to a higher energy level.

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    Color from light absorption

    The color observed in a molecule that absorbs visible light arises from the specific wavelength of light that it absorbs.

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    Vibrational transitions

    Vibrational transitions are not considered electronic transitions, as they involve changes in the vibrational energy levels of a molecule, not the electronic energy levels.

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    Electronic transitions and light emission

    Electronic transitions are not always accompanied by the emission of light. Nonradiative decay is an example of an electronic transition that doesn't produce light.

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    Highest energy radiation

    Cosmic rays, with the highest energy levels in the electromagnetic spectrum, carry the most energy out of all forms of radiation.

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