Chapter 6 Section 5 Part 1: Molecular Geometry VSEPR

Chapter 6 Section 5 Part 1: Molecular Geometry-VSEPR Theory

​Introduction

• ​Properties of molecules depend on the arrangement of the molecules

  • ​Molecular Geometry: The three-dimensional arrangement of Atoms in space

    • ​Chemical Formulas reveal little about a molecule's geometry

    • ​Two methods are used to reveal the shapes

      • ​VSEPR

      • ​Hybridization

​VSEPR

• ​Valence-Shell, Electron Pair Repulsion

  • ​The Repulsion between the sets of valence electrons surrounding an atom forces sets of atoms to be oriented as far apart as possible

    • ​Think of a group of magnets, each one moves until they are balanced

• ​VSPER Shows what type of shape the atoms of a molecule form

​How VSEPR Works

• ​Let's look at the molecule BeF₂

  • ​Remember Beryllium is special and does not follow the octet rule

  • ​According to VSEPR, the shared electron pairs will be as far away from each other as possible

    • ​The only way this can happen is if they are in a straight line

​VSPER Theory and unshared Electron Pairs

• ​Some molecules have unshared electron pairs in their structures

  • ​Ammonia (NH₃₎

  • ​Water (H₂O)

• ​VSEPR Treats these unpaired electrons as though they occupy the space around the central atom, but do not affect how we see the shape

• ​In a generic formula unpaired electrons are represented by the letter E

​A & B = atoms

​E= Loose electron Pairs

​Practice

• ​Use VSPER theory to predict the molecular geometry of boron Trichloride BCl₃

  • Start with electron dot notation of BCl₃

  • ​What Type of Molecule is BCl_3?

    • ​AB₃

      • ​This shape Corresponds to Trigonal Planar