2.4.1 - VSEPR Theory 

Introduction

• ^^VSEPR^^ - Valence Shell Electron Pair Repulsion.
• VSEPR is only for covalent bonds
• Refers to the distribution of electrons so that they have the least amount of repulsion.
  • This means that bonding regions will be as far away from each other as possible (repulsion)
• VSEPR results in the creation of five different shapes, depending on the number of bonding regions and lone pairs.
  • Linear
  • V-Shaped
  • Trigonal planar
  • Trigonal pyramidal
  • Tetrahedral
• ^^Bonding regions^^ - electrons shared between two atoms
• ^^Lone pairs^^ - electrons that are not bonded to any other atom
• Central atoms have the lowest electronegativity of the entire molecule.
• Molecular shape (VSEPR) can be determined from number of electron regions and lone pairs.
• Structure affects polarity.

VSEPR Shapes

Linear Molecules

• Have either one or two bonding regions that are around a central atom.

• e.g - Cl2, CO2, HCl

  

• Note that it refers to bonding regions, specifically - double and triple bonds (see above: CO2) can still be linear molecules.

V-Shaped Molecules

• Have two bonding regions and one/two lone pairs around a central atom.

• Will always be polar.

• e.g H2O, SO2, H2S

  

Trigonal Planar

• Have three bonding regions around the central atom.

• Molecule itself is flat.

• Can be polar or nonpolar - if molecule is symmetrical, it is nonpolar. Else, polar.

• e.g SO3, BF3, H2CO

  

Trigonal Pyramidal

• Have three bonding regions and one lone pair of electrons.

• Will always be polar.

  

• e.g PH3, NH3, H3O+

Tetrahedral

• Have four bonding regions.

• Can be polar or nonpolar - if molecule is symmetrical, it is nonpolar. Else, polar.

  

• e.g CH4, PO4(3-), SO4(2-)