Valence shell electron pair repulsion (VSEPR) model:

1. Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. The idea here is that the bonding and nonbonding pairs around a given atom will be positioned as far apart as possible. This chart is NOT provided on the AP exam!

2. # of atoms bonded tocentral atom # lone pairs on central atom Arrangement ofelectron pairs Molecular Geometry Class linear linear B B VSEPR A = central atom B = atoms bonded to central atom E = lone pairs (non-bonding) of electrons on central atom AB2 2 0 Bond angle

3. 0 lone pairs on central atom Cl Be Cl 2 atoms bonded to central atom

4. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar Arrangement ofelectron pairs Molecular Geometry Class VSEPR AB2 2 0 linear linear AB3 3 0

6. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar Arrangement ofelectron pairs Molecular Geometry bent Class VSEPR – Trigonal Planar arrangement trigonal planar trigonal planar AB3 3 0 AB2E 2 1

7. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class tetrahedral tetrahedral VSEPR AB2 2 0 linear linear AB4 4 0

9. # of atoms bonded tocentral atom # lone pairs on central atom trigonal pyramidal tetrahedral Arrangement ofelectron pairs Molecular Geometry Class VSEPR – Tetrahedral Arrangement tetrahedral tetrahedral AB4 4 0 AB3E 3 1

10. # of atoms bonded tocentral atom # lone pairs on central atom trigonal pyramidal Arrangement ofelectron pairs Molecular Geometry AB3E 3 1 tetrahedral Class bent tetrahedral O H H VSEPR – Tetrahedral Arrangement tetrahedral tetrahedral AB4 4 0 AB2E2 2 2

11. In these molecules, the arrangement of the electron pairs predict tetrahedral geometry. Why is the geometry different from predicted? Lone pairs require more room than bonding pairs and tend to compress the angles between the bonding pairs.

12. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class trigonal bipyramidal trigonal bipyramidal VSEPR AB2 2 0 linear linear tetrahedral tetrahedral AB4 4 0 AB5 5 0

14. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal See-Saw (distorted tetrahedron) Arrangement ofelectron pairs Molecular Geometry Class VSEPR – Trigonal Bipyramidal Arrangement trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB4E 4 1

15. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal See-Saw Arrangement ofelectron pairs Molecular Geometry AB4E 4 1 Class trigonal bipyramidal T-shaped F F Cl F VSEPR – Trigonal Bipyramidal Arrangement trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB3E2 3 2

16. # of atoms bonded tocentral atom # lone pairs on central atom trigonal bipyramidal See-Saw Arrangement ofelectron pairs Molecular Geometry AB4E 4 1 Class trigonal bipyramidal T-shaped AB3E2 3 2 trigonal bipyramidal linear I I I VSEPR – Trigonal Bipyramidal Arrangement trigonal bipyramidal trigonal bipyramidal AB5 5 0 AB2E3 2 3

17. # of atoms bonded tocentral atom # lone pairs on central atom trigonal planar trigonal planar AB3 3 0 Arrangement ofelectron pairs Molecular Geometry Class trigonal bipyramidal trigonal bipyramidal AB5 5 0 octahedral octahedral VSEPR AB2 2 0 linear linear tetrahedral tetrahedral AB4 4 0 AB6 6 0

19. octahedral octahedral AB6 6 0 # of atoms bonded tocentral atom # lone pairs on central atom square pyramidal octahedral Arrangement ofelectron pairs Molecular Geometry Class F F F Br F F VSEPR – Octahedral Arrangement AB5E 5 1

20. octahedral octahedral AB6 6 0 # of atoms bonded tocentral atom # lone pairs on central atom square pyramidal octahedral AB5E 5 1 Arrangement ofelectron pairs Molecular Geometry Class square planar octahedral F F Xe F F VSEPR – Octahedral Arrangement AB4E2 4 2

21. O O S What are the molecular geometries of SO2 and SF4? (In SF4, S uses an expanded octet of 10.) F S S F O O F F Predicting Molecular Geometry • Draw Lewis structure for molecule. • Count number of lone pairs on the central atom and number of atoms bonded to the central atom. • Use VSEPR to predict the geometry of the molecule. AB4E See-Saw (distorted Tetrahedron) AB2E bent

22. F H d- d+ Dipole Moments and Polar Molecules electron rich region electron poor region A molecule such as HF that has a center of positive charge and a center of negative charge is said to have a dipole moment. The dipole moment is often represented by an arrow pointing to the negative charge center with the tail of the arrow indicating the positive center of charge.

23. Which of the following molecules have a dipole moment? H2O, CO2, SO2, and CH4 O O S H H H O O O C H H C H dipole moment polar molecule dipole moment polar molecule no dipole moment nonpolar molecule no dipole moment nonpolar molecule