Chemistry VSEPR Theory Quiz
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Questions and Answers

What does the Steric Number (SN) represent?

  • The sum of atoms bonded to a central atom and lone pairs on that atom. (correct)
  • The number of double bonds present around a central atom.
  • The molecular weight of a compound.
  • The total number of valence electrons in a molecule.

    • Which of the following electron-pair geometries corresponds to a Steric Number of 4?

  • Trigonal planar
  • Tetrahedral (correct)
  • Trigonal bipyramidal
  • Linear

    • How does the presence of lone pairs affect molecular geometry compared to electron-pair geometry?

  • Lone pairs can change angles and overall geometry. (correct)
  • Lone pairs have no effect on molecular geometry.
  • Lone pairs only affect bond angles and not geometry.
  • Molecular geometry is always identical to electron-pair geometry.

    • What bond angle is expected for a molecule with a trigonal planar electron-pair geometry?

    <p>120 degrees</p> Signup and view all the answers

    Which of the following statements about bond angles is true when lone pairs are present?

    <p>Bond angles are typically less than theoretical angles.</p> Signup and view all the answers

    What is the electron-pair geometry for a molecule with a Steric Number of 2?

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

    How does the repulsion between bonding pairs compare to that of lone pairs?

    <p>Lone pairs exert greater repulsion than bonding pairs.</p> Signup and view all the answers

    If a molecule has one lone pair and three bonded pairs, what is its molecular geometry?

    <p>Trigonal pyramidal</p> Signup and view all the answers

    What does the Valence-Shell Electron Pair Repulsion Theory (VSEPR) predict?

    <p>The arrangement of valence electron pairs around a central atom that minimizes their mutual repulsion.</p> Signup and view all the answers

    What is the steric number (SN) for a linear molecular geometry?

    <p>2</p> Signup and view all the answers

    The molecular geometry will be the same as the electron-pair geometry if there are no ______ on the central atom.

    <p>lone pairs</p> Signup and view all the answers

    In a trigonal planar geometry, what is the bond angle?

    <p>120°</p> Signup and view all the answers

    Match the steric number with the corresponding electron-pair geometry:

    <p>2 = Linear 3 = Trigonal Planar 4 = Tetrahedral 5 = Trigonal Bipyramidal 6 = Octahedral</p> Signup and view all the answers

    Repulsion between lone pairs and bonding pairs is less than repulsion between bonding pairs.

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

    Study Notes

    Valence-Shell Electron Pair Repulsion (VSEPR) Theory

    • Predicts the arrangement of valence electron pairs around a central atom.
    • Minimizes mutual repulsion for lowest energy orientations.
    • Electron pair geometry describes the 3D arrangement of bonding and lone electron pairs around a central atom.
    • Molecular geometry describes the 3D arrangement of atoms in a molecule.
    • Electron-pair geometry equals molecular geometry only when no lone pairs are present.

    Steric Number (SN) and Electron-Pair Geometry

    • SN is the sum of atoms bonded to the central atom plus lone pairs on the central atom.
    • SN determines electron-pair geometry:
      • SN = 2: linear
      • SN = 3: trigonal planar
      • SN = 4: tetrahedral
      • SN = 5: trigonal bipyramidal
      • SN = 6: octahedral

    Electron-Pair vs. Molecular Geometry

    • Molecular geometry differs from electron-pair geometry when lone pairs are present on the central atom.
    • Molecular geometry is based on the positions of bonded atoms only.

    Bond Angles and VSEPR

    • Bond angle is the angle between two atoms bonded to a third.
    • Electron-pair geometry provides a theoretical bond angle.
    • Lone pairs influence bond angles due to greater repulsion:
      • Lone pair-lone pair repulsion > lone pair-bonding pair repulsion > bonding pair-bonding pair repulsion.
      • Lone pair repulsion > double bond repulsion > single bond repulsion.
      • Two lone pairs cause greater repulsion than one.
    • In molecules with lone pairs, bond angles are less than theoretical angles.

    Valence-Shell Electron Pair Repulsion (VSEPR) Theory

    • Predicts the arrangement of valence electron pairs around a central atom.
    • Minimizes electron repulsion to achieve lowest energy.
    • Electron-pair geometry describes the 3D arrangement of bonding and lone pairs around a central atom.
    • Molecular geometry describes the 3D arrangement of atoms in a molecule.
    • Electron-pair geometry equals molecular geometry when no lone pairs are present.

    Steric Number (SN) and Electron-Pair Geometry

    • SN is the sum of atoms bonded to a central atom plus lone pairs on that atom.
    • SN determines electron-pair geometry:
      • SN = 2: Linear
      • SN = 3: Trigonal planar
      • SN = 4: Tetrahedral
      • SN = 5: Trigonal bipyramidal
      • SN = 6: Octahedral

    Differences Between Electron-Pair and Molecular Geometry

    • Lone pairs affect molecular geometry.
    • Molecular geometry differs from electron-pair geometry when lone pairs are present. It's defined by the positions of the bonded atoms.

    Bond Angles and Repulsion

    • Bond angle: Angle between two atoms bonded to a central atom.
    • Electron-pair geometry provides theoretical bond angles.
    • Lone pairs cause deviations from theoretical angles due to increased repulsion.
    • Repulsion strength: lone pair > double bond > single bond.
    • Multiple lone pairs increase repulsion compared to a single lone pair.
    • Molecules with lone pairs have bond angles less than the theoretical angles.

    SN = 2 (Linear)

    • Electron-pair geometry: Linear
    • Number of bonded atoms: 2
    • Number of lone pairs: 0
    • Molecular geometry: Linear
    • Bond angle: 180°
    • Example: CO₂
    • Hybridization: sp

    SN = 3 (Trigonal Planar)

    • Electron-pair geometry: Trigonal planar

    • Number of bonded atoms: 3

    • Number of lone pairs: 0

    • Molecular geometry: Trigonal planar

    • Bond angle: 120°

    • Example: CH₂O

    • Hybridization: sp²

    • Electron-pair geometry: Trigonal planar

    • Number of bonded atoms: 2

    • Number of lone pairs: 1

    • Molecular geometry: Bent (angular)

    • Bond angle: less than 120° (due to lone pair repulsion)

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    Description

    Test your understanding of Valence-Shell Electron Pair Repulsion (VSEPR) theory and its applications in predicting molecular geometry. This quiz covers key concepts including steric number and the differences between electron-pair and molecular geometry.

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