1. GEOMETRY AND POLARITY OF MOLECULES

2. GEOMETRY – arrangement in space of atoms in a molecule

3. VALENCE SHELL ELECTRON-PAIR REPULSION (VSEPR) model
Accounts for the geometrical arrangement of shared and unshared pairs around a central atom in terms of repulsions between electron pairs.

4. Number of groups Molecular structure Bond angles 2 linear 180o 3
In determining the geometry of the molecule, bonds and unshared electron pairs are considered as groups. Single bonds, double bonds and triple bonds are basically treated as if they are all the same.
Number of groups
Molecular structure
Bond angles 2
linear
180o 3
Trigonal planar
120o 4
tetrahedral
109.3o 5
Trigonal bipyramid
90o, 120o, 180o 6
octahedral
90o

5. H2O
Shape = bent or v-shaped
Bond angle = o

6. NH3
Shape = trigonal pyramid
Bond angle = 107o

7. CCl4
Shape = tetrahedral
Bond angle = 109.3o

8. SF6
Shape = octahedral
Bond angle = 90o

9. # regions of high electron density
molecule
Lewis structure
# regions of high electron density
BeCl2
                                2
BF3 3
HCN
SO3
                                
CO2
                              
NO2
                             
CH4 4
NH3
           
PCl5 5
SF6 6

10. BOND POLARITY
Due to the differences in the electronegativity of the elements bonded covalently.
the electrons are concentrated at the more electronegative end of the bond, thus giving it a partial negative charge (δ-) and the less electronegative element, a partial positive charge (δ+).
Non polar since electronegativity is the same H H δ+ δ-
Polar since Cl is more electronegative than H H Cl C H
C-H bond is considered as non-polar

11. POLARITY OF THE MOLECULE
- Considers the net dipole moment (net polarity) of all the bonds present in the molecule.
NET DIPOLE MOMENT = 0 = = O C O δ- δ- δ+ δ-
NET DIPOLE MOMENT = O H H δ+ δ+

12. H C H H H H H C Cl H CH4 CH3Cl NET DIPOLE MOMENT = 0 δ- δ+

13. Cl Cl C H H H Cl C Cl H CH2Cl2 CH2Cl2 δ- δ+ δ- δ+ NET DIPOLE MOMENT =