Chemistry VSEPR Theory Quiz

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)

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.