Geometry of Molecules

1
Geometry of Molecules

• VSEPR Theory

2
Valence Shell Electron Pair Repulsion Theory
(VSEPR)

• The geometry of the molecule at any given
  central atom is determined by the repulsions of
  both bonding and nonbonding (lone pair) electrons
  in the valence shell.

3
Hybridization

• When atoms join to form molecules, the electron
  density regions change.

4
Hybridization

• The process of mixing different orbitals of
  the same atom to form a new set of equivalent
  orbitals is termed hybridization.
• The shape of the molecule depends of the
  number of electron pairs on the central atom and
  the orientation of the hybrid orbitals.

5
VSEPR

• Shapes expected for different numbers of electron
  pairs

6
Two Pairs of Electrons

• BeH2
• Linear molecule

sp hybrid
There are two pairs of electrons on the central
atom, beryllium.
7
Linear Molecule
8
Three Pairs of Electrons

• BCl3
• Planar triangular, 120o

There are three pairs of electrons on the central
atom, boron.
sp2 hybrid
9
Planar Triangular Molecule
10
Hybrid Orbitals
11
Four Pairs of Electrons
CH4 Tetrahedral, 109.5o There are four pairs of
electrons on the central atom, carbon.
sp3 hybrid
12
Tetrahedral Molecule
13
Organic Compounds

• A huge number of the compounds that exist on
  Earth are carbon-containing compounds that have
  the tetrahedral shape around each carbon atom.

14
Four Pairs of Electrons
15
Five Pairs of Electrons
PCl5 Trigonal bipyramidal 90o and 120o
sp3d hybrid
16
sp3d and sp3d2 Hybrid Orbitals
17
Six Pairs of Electrons
SF6 Octahedral, 90o sp3d2 hybrid
18
VSEPR Theory

• Molecular geometry affects the characteristics
  of all compounds.
• Learn more with the
• VESPR Molecular Model Kit