Valence Shell Electron Pair Repulsion Theory VSEPR Theory Valence Shell Electron Pair Repulsion Theory “Atomium Building”, Andre Waterkeyn (architect), 1958

VSEPR Theory A method for predicting the shape of a molecule from the knowledge of the groups of electrons around a central atom. The shape of a molecule is very important for its physical and chemical properties.

Demo: Water and a Balloon

Electron pairs (bonding and nonbonding electrons) repel one another Electron pairs (bonding and nonbonding electrons) repel one another. As a result, the electron pairs remain as far apart as possible from another as possible to minimize the repulsion.

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 linear

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4 Tetrahedral

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4 Tetrahedral 5

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4 Tetrahedral 5 Trigonal bipyramidal

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4 Tetrahedral 5 Trigonal bipyramidal 6

Electron Pairs Around a Central Atom (bonding or nonbonding Arrangement Diagram 2 Linear 3 Trigonal planer 4 Tetrahedral 5 Trigonal bipyramidal 6 Octahedral

Lone Pairs The shapes on the previous slides are the general arrangements for electron domains. Whether the domain is a lone pair or a bonding pair affects the geometry of the molecule. Repulsion Strength lone pair-lone pair  lone pair-bond pair  bond pair-bond pair

Geometries 2 Linear 180 # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 2 Linear 180

Geometries 3 120 Trigonal Planer # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 3 Trigonal Planer 120

Geometries 3 120 2 1 Bent <120 Trigonal Planer # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 3 Trigonal Planer 120 2 1 Bent <120

Geometries 4 109.5 Tetra-hedral # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 4 Tetra-hedral 109.5

Geometries 4 109.5 3 1 Tetra-hedral Trigonal Pyrami-dal <109.5 # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 4 Tetra-hedral 109.5 3 1 Trigonal Pyrami-dal <109.5

Geometries 4 109.5 3 1 2 Bent Tetra-hedral Trigonal Pyrami-dal # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 4 Tetra-hedral 109.5 3 1 Trigonal Pyrami-dal <109.5 2 Bent

Geometries 5 90 & 120 Trigonal Bipyramidal # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 5 Trigonal Bipyramidal 90 & 120

Geometries 5 4 1 90 & 120 <90 & See-saw <120 # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 5 Trigonal Bipyramidal 90 & 120 4 1 See-saw <90 & <120

Geometries 5 4 1 3 2 90 90 & 120 <90 & See-saw <120 T-shape # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 5 Trigonal Bipyramidal 90 & 120 4 1 See-saw <90 & <120 3 2 T-shape 90

Geometries 5 4 1 3 2 90 90 & 120 See-saw <90 & <120 T-shape # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 5 Trigonal Bipyramidal 90 & 120 4 1 See-saw <90 & <120 3 2 T-shape 90 Linear 180

Geometries 6 90 Octahedral # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 6 Octahedral 90

Geometries 6 5 1 90 Square Pyramidal <90 Octahedral # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 6 Octahedral 90 5 1 Square Pyramidal <90

Geometries 6 5 1 4 2 90 Square Pyramidal <90 Square Planer # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 6 Octahedral 90 5 1 Square Pyramidal <90 4 2 Square Planer

Geometries 6 5 1 4 2 3 90 Square Pyramidal <90 Square Planer # of Electron Domains # of Bonds # of Lone Pairs Molecular Geometry Name Model Approx. Bond Angle 6 Octahedral 90 5 1 Square Pyramidal <90 4 2 Square Planer 3 T-Shape

Seesaw

Molecular Polarity Molecules can be polar or nonpolar. Molecular polarity depends on the symmetry of the molecule. (Remember, polar means “having two sides”)

Nonpolar Molecules Nonpolar molecules are symmetrical and have dipoles that cancel out.

Polar Molecules Polar molecules are asymmetrical and have dipoles that do not cancel out.

Practice Determine whether each of the following molecules is polar or nonpolar. Polar

Practice Determine whether each of the following molecules is polar or nonpolar. Nonpolar

Practice Determine whether each of the following molecules is polar or nonpolar. Nonpolar

Practice Determine whether each of the following molecules is polar or nonpolar. Polar