IIIIII II. Molecular Geometry Ch. 9 – Molecular Structure

A. VSEPR Theory n Valence Shell Electron Pair Repulsion Theory n Electron pairs orient themselves in order to minimize repulsive forces.

A. VSEPR Theory n Types of e - Pairs  Bonding pairs - form bonds  Lone pairs - nonbonding e - Lone pairs repel more strongly than bonding pairs!!!

A. VSEPR Theory n Lone pairs reduce the bond angle between atoms. Bond Angle

n Draw the Lewis Diagram. n Tally up e - pairs on central atom.  double/triple bonds = ONE pair n Shape is determined by the # of bonding pairs and lone pairs. Know the common shapes & their bond angles! B. Determining Molecular Shape

C. Common Molecular Shapes 2 total 2 bond 0 lone LINEAR 180° BeH 2

3 total 3 bond 0 lone TRIGONAL PLANAR 120° BF 3 C. Common Molecular Shapes

3 total 2 bond 1 lone BENT 104.5° SO 2

4 total 4 bond 0 lone TETRAHEDRAL 109.5° CH 4 C. Common Molecular Shapes

4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107° NH 3 C. Common Molecular Shapes

4 total 2 bond 2 lone BENT 104.5° H2OH2O C. Common Molecular Shapes

5 total 5 bond 0 lone TRIGONAL BIPYRAMIDAL 120°/90° PCl 5 C. Common Molecular Shapes

6 total 6 bond 0 lone OCTAHEDRAL 90° SF 6 C. Common Molecular Shapes

n PF 3 4 total 3 bond 1 lone TRIGONAL PYRAMIDAL 107° F P F F D. Examples

n CO 2 O C O 2 total 2 bond 0 lone LINEAR 180° D. Examples

C. Bond Polarity n Electronegativity Trend  Increases up and to the right.

A. Dipole Moment n Direction of the polar bond in a molecule. n Arrow points toward the more e - neg atom. H Cl ++ --

B. Determining Molecular Polarity n Depends on:  dipole moments  molecular shape

B. Determining Molecular Polarity n Nonpolar Molecules  Dipole moments are symmetrical and cancel out. BF 3 F F F B

B. Determining Molecular Polarity n Polar Molecules  Dipole moments are asymmetrical and don’t cancel. net dipole moment H2OH2O H H O

CHCl 3 H Cl B. Determining Molecular Polarity n Therefore, polar molecules have...  asymmetrical shape (lone pairs) or  asymmetrical atoms net dipole moment

C. Bond Polarity n Most bonds are a blend of ionic and covalent characteristics. n Difference in electronegativity determines bond type.

EN Difference n Nonpolar n Moderately Polar Covalent n Very Polar Covalent n > 2.0 Ionic

C. Bond Polarity Examples: n Cl 2 n HCl n NaCl =0.0 Nonpolar =0.9 Moderately Polar Covalent =2.1 Ionic

C. Bond Polarity n Electronegativity  Attraction an atom has for a shared pair of electrons.  higher e - neg atom   -  lower e - neg atom   + ____

n Nonpolar Covalent Bond  e - are shared equally  symmetrical e - density  usually identical atoms C. Bond Polarity

++ -- n Polar Covalent Bond  e - are shared unequally  asymmetrical e - density  results in partial charges (dipole)

n Nonpolar n Polar n Ionic View Bonding Animations.Bonding Animations C. Bond Polarity