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Valence Shell Electron Pair Repulsion Model

Tags
Chem/Molecule
Cegep/2
Word count
262 words
Reading time
2 minutes

Molecular geometry model
Abbr. VSEPR model

Rules:

  • Can be applied to any resonance model
  • Only consider the central atom
    • A = central atom
    • B = bonding electron pairs
    • E = lone electron pairs
  • Electron pairs:
    • Determine shape of molecule
    • Double and triple bonds considered as single bonds
    • Repel each other to be as far apart as possible
      • Lone pairs repel more strongly than bonding pairs

Steps:

  1. Draw Lewis structure
  2. Recognize the VSEPR model
Class of molecule# electron pairs# bonding pairs# lone pairsArrangementMolecular geometry
ABA2220LinearLinear
ABA3330Trigonal planarTrigonal planar
ABA2E321Trigonal planarBent
ABA4440TetrahedralTetrahedral
ABA3E431TetrahedralTrigonal pyramidal
ABA2EA2422TetrahedralBent
ABA5550Trigonal bipyramidalTrigonal bipyramidal
ABA4E541Trigonal bipyramidalDistorted tetrahedron
ABA3EA2532Trigonal bipyramidalT-shaped
ABA2EA3523Trigonal bipyramidalLinear
ABA6660OctahedralOctahedral
ABA5E651OctahedralSquare pyramidal
ABA4EA2642OctahedralSquare planar

Examples

Predict the arrangement of electron pairs, the geometry and polarity of:

IA3A

e=37+1=22

  • Arrangement: trigonal bipyramidal
  • Molecular geometry: linear
  • Non-polar because it has rotational symmetry

HNOA3

e=1+5+36=24

  • Arrangement: trigonal planar
  • Molecular geometry: trigonal planar
  • Polar because hydrogen breaks rotational symmetry

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