### - Lewis structures and bonds

```- LEWIS STRUCTURES AND BONDS
- BONDING THEORIES
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)
 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.
 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
2O
 O═C═O or O::C::O
 Carbon monoxide has a triple covalent bond.
C O  C≡O
OR
C⋮⋮O
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.
 The shape of a molecule of CO2 is linear.
 The shape of a molecule of HCN is linear.
 The shape of a molecule of CH4 is
tetrahedral.
 The shape of a molecule of NH3 is trigonal
pyramidal.
 The shape of a molecule of H2O is bent.
 According to VSEPR theory repulsive forces
between unshared pairs of electrons causes
water molecules to have their shape.
Bond angle =
109.5 degrees
Example: CH4
Bond angle =
106.5 degrees
Example: NH3
Bond angle =
104.5 degrees
Example: H2O
Bond angle =
120 degrees
Example: CO32-
Bond angle =
118.6 degrees
Example: O3
Bond angle =
180 degrees
Example: CO2
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
 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
```