1. - Lewis structures and bonds - bonding theories

2. Lewis Structures and Bonding
Use NASB to draw dot diagrams.
N – electrons needed to fill valence (8 or 2)
A- electrons available in atom
S – electrons shared = N – A
B – formed bonds (S divided by 2)

3. In Cl2, the total number of unshared pairs of electrons is 6.
Cl Cl  Cl―Cl or Cl:Cl
The diatomic molecule N2 contains a triple covalent bond.
N N  N≡N or N⋮⋮N
In the N2 molecule, there is only one unshared pair of electrons in each nitrogen atom.

4. The HI molecule contains only one single covalent bond.
H• I  H―I or H:I
There are 2 double covalent bonds in a molecule of CO2.
C O  O═C═O or O::C::O
Carbon monoxide has a triple covalent bond.
C O  C≡O OR C⋮⋮O

5. Bonding Theories
According to VSEPR theory, molecules adjust their shapes to keep pairs of valence electrons as far apart as possible.
VSEPR –
Valence Shell Electron Pair Repulsion
A stereoactive set is a shared pair or an unshared pair of electrons around the central atom.

6. The shape of a molecule of CO2 is linear.

7. The shape of a molecule of HCN is linear.

8. The shape of a molecule of CH4 is tetrahedral.

9. The shape of a molecule of NH3 is trigonal pyramidal.

10. The shape of a molecule of H2O is bent.

11. According to VSEPR theory repulsive forces between unshared pairs of electrons causes water molecules to have their shape.

12. Bond angle =
109.5 degrees
Example: CH4
Bond angle =
106.5 degrees
Example: NH3

13. Bond angle =
104.5 degrees
Example: H2O
Bond angle =
120 degrees
Example: CO32-

14. Bond angle =
118.6 degrees
Example: O3
Bond angle =
180 degrees
Example: CO2

15. Intermolecular Forces
Intermolecular forces – forces between 2 molecules
Van der Waals forces - weakest attractions between molecules
Dipole interactions – polar molecules attracted to one another
Dispersion forces – caused by the motion of electrons

16. Hydrogen bonds – strongest intermolecular forces
Hydrogen covalently bonded to a very electronegative atom is also bonded to an unshared electron pair of another electronegative atom.
H2O is a polar molecule.
2 H• O  H:O:H