1. MOLECULAR GEOMETRY
Bonding Unit

2. Molecule adopts the shape that minimizes the electron pair repulsions.
MOLECULAR GEOMETRY
VSEPR
Valence Shell Electron Pair Repulsion theory.
Molecule adopts the shape that minimizes the electron pair repulsions.

3. Some Common Geometries
Linear
Trigonal Planar
Tetrahedral

4. Steps for Predicting Molecular structure using the VSEPR Model
Draw the Lewis structure.
Count the electron pairs and arrange them in a way to reduce repulsion.
Determine the positions of the atoms from the way the electrons pairs are shared.
Determine the name of the molecular structure from the position of the atoms.

5. Rules for Predicting Molecular Structure using the VSEPR Model
2 pairs of electrons on a central atom in a molecule are always placed 180o apart (linear).
Three pairs of electrons on a central atom in a molecule are always placed 120o apart on the same plane as the central atom (Trigonal Planar).
Four pairs of electrons on a central atom in a molecule are always placed 109.5o apart (tetrahedral).

6. Rules for Predicting Molecular Structure using the VSEPR Model
When every pair of electrons on the central atom is shared with another atom, the molecular structure has the same name as the arrangement of the electron pairs.
Number of Pairs
Name of Arrangement 2
Linear 3
Trigonal Planar 4
tetrahedral

7. Rules for Predicting Molecular Structure using the VSEPR Model
When one or more of the electron pairs around a central atom are lone pairs, the name for the molecular geometry is different from the arrangement of electron pairs.

8. Structure Determination
by VSEPR
Water, H2O
The electron pair geometry is TETRAHEDRAL
2 bond pairs
2 lone pairs
The molecular geometry is BENT.

9. Water, H2O
Electron Arrangement= Tetrahedral
Molecular Geometry= Bent

10. Methane, CH4 Electron Arrangement= Tetrahedral
Molecular Geometry= Tetrahedral

11. Ammonia, NH3 Electron Arrangement= Tetrahedral
Molecular Geometry= Trigonal Pyramid