Go to the following site and see resonance structures and bond length http://www2.gasou.edu/chemdept/general/molecule/lewis.htm

The VSEPR theory or model The Valence Shell Electron Pair Repulsion (VSEPR) model: is based on the number of regions of high electron density around a central atom (effective pairs). can be used to predict structures of molecules or ions that contain only non-metals by minimizing the electrostatic repulsion between the regions of high electron density. Effective pairs must be as far as possible from each other. can also be used to predict structures of molecules or ions that contain multiple bonds or unpaired electrons. does fail in some cases, that is there are exceptions. http://www.chem.purdue.edu/gchelp/vsepr/

The VSEPR rules Draw the Lewis structure for the molecule or ion. Count the effective pairs or total number of regions of high electron density (bonding and unshared electron pairs) around the central atom. Double and triple bonds count as one effective pair (ONE REGION OF HIGH ELECTRON DENSITY). An unpaired electron counts as one effective pair (ONE REGION OF HIGH ELECTRON DENSITY). For molecules or ions that have resonance structures, you may use any one of the resonance structures. http://www.chem.purdue.edu/gchelp/vsepr/

# regions of high electron density Molecule Lewis Structure # regions of high electron density (EFFECTIVE PAIRS) BeCl2 BF3 SHAPE Linear 2 Trigonal Planar 3 http://henson1.ssu.edu/~dfrieck/212/vsepr.htm

# regions of high electron density Molecule Lewis Structure # regions of high electron density (EFFECTIVE PAIRS) CH4 NH3 SHAPE 4 Tetrahedral Trigonal Pyramidal 4 (3 bonded 1 lone pair)

# regions of high electron density Molecule Lewis Structure # regions of high electron density (EFFECTIVE PAIRS) H2O PF5 SHAPE Bent or angular 4 (2 bonded 2 lone pairs) 5 Trigonal Bipyramidal

# regions of high electron density Molecule Lewis Structure # regions of high electron density (EFFECTIVE PAIRS) SF6 CO2 SHAPE Octahedral 6 Linear 180° 2

ABE NOTATION Since the molecular geometry is determined by how many bonding and non-bonding electron groups surround the central atom, the first thing one needs to do is count how many of each there are. There is a notation that simplifies this bookkeeping: ABxEy The A represents the central atom, B represents the electron groups that form bonds to other atoms, and E represents the non-bonding electron groups. The subscripts, x and y, indicate how many of each kind are present. http://chemlabs.uoregon.edu/GeneralResources/models/vsepr.html

An incidental benefit of using the ABE notation is that it provides a convenient way of remembering the hybridization at the central atom. The total number of substituents (bonding plus non-bonding groups) is equal to the number of atomic orbitals that participate in the hybrid orbital. Molecule ABE representation # of substituents Hybridization CH4 AB4 4 sp3 NH3 AB3E H2O AB2E2 CO2 AB2 2 sp SF6 AB6 6 sp3d2 I3- ion AB2E3 5 sp3d http://chemlabs.uoregon.edu/GeneralResources/models/vsepr.html

AB4 bonding groups: 4 non-bonding groups: 0 AB3E bonding groups: 3 non-bonding groups: 1 AB2E2 bonding groups: 2 non-bonding groups: 2                                CH4 methane               NH3 ammonia               H2O water AB2 bonding groups: 2 non-bonding groups: 0                                       CO2 Carbon Dioxide Note that bonding "electron groups" does not necessarily imply single bonds; it can mean double or triple bonds as well: http://chemlabs.uoregon.edu/GeneralResources/models/vsepr.html

Displayed in the following table are the five most important electronic symmetries. Each row in the table is linked to a page that shows the different molecular symmetries possible for that electronic symmetry. Class Hybridization Electronic Symmetry AB2 sp linear AB3 sp2 trigonal planar AB4 sp3 tetrahedral AB5 sp3d trigonal bipyramidal AB6 sp3d2 octahedral http://chemlabs.uoregon.edu/GeneralResources/models/vsepr.html

Go to the following site and see VSEPR to visualize orbitals and shapes http://www2.gasou.edu/chemdept/general/molecule/lewis.htm http://gaia.fc.peachnet.edu/tutor/Three-to-Six-Domains.html http://www.chem.purdue.edu/gchelp/vsepr/structur2.html Note: These sites have also been used in the pervious notes together with the sources cited in specific slides

Polar and non polar molecules A molecule like HF is said to be dipolar or to have a dipole moment + - H F Any diatomic molecule that has a polar bond will show a dipole moment

Polyatomic molecules with polar bonds Polar: if the dipoles of the bonds don’t cancel out. Polyatomic molecules with polar bonds cab be Non Polar: if the dipoles of the bonds cancel out because of the symmetric shape.

Example of Polar Polyatomic Molecules NH3 H2O + - - + The dipoles of the bonds don’t cancel out so the molecule has a dipole moment. These molecules are dipoles.

Example of Non-Polar Polyatomic Molecules BF3 CO2 CCl4 Cl Cl Cl Cl The dipoles of the bonds cancel out because of the symmetric shape. These molecules are non-polar molecules