Section 12.4
Structure of Molecules
Warm-up
• Draw the Lewis Structure for the following covalent
bonds.
• CH
4
• NH3
• H2O
Section 12.4
Structure of Molecules
Objectives
1. SWBAT understand molecular structure, be able to
predict molecular geometry from the number of electron
pairs and to apply the VSEPR model to molecules with
double bonds in a virtual laboratory.
Section 12.4
Structure of Molecules
Polar Covalent Bonds – 2a.3
• When atoms of different electronegativities bond, they
don’t share electrons equally.
• This unequal sharing of electrons results in a polar
covalent bond.
How are polar covalent bonds
different from regular (nonpolar)
covalent bonds?
Section 12.4
Structure of Molecules
Nonpolar Covalent Bond
Section 12.4
Structure of Molecules
Slightly Polar Covalent Bond
Section 12.4
Structure of Molecules
Polar Covalent Bond
Section 12.4
Structure of Molecules
A. Molecular Structure
• Three dimensional arrangement of the atoms in a
molecule
– Water - bent
LQHS
Section 12.4
Structure of Molecules
A. Molecular Structure
• Linear structure – atoms in a line
– Carbon dioxide
Section 12.4
Structure of Molecules
A. Molecular Structure
• Trigonal planar – atoms in a triangle
– BF3
Section 12.4
Structure of Molecules
A. Molecular Structure
• Tetrahedral structure
– methane
Section 12.4
Structure of Molecules
B. The VSEPR Model
• Valence shell electron pair repulsion (VSEPR) model
– Molecular structure is determined by minimizing
repulsions between electron pairs
Section 12.4
Structure of Molecules
B. The VSEPR Model
Two Pairs of Electrons
• BeCl2
– 180o - linear
Section 12.4
Structure of Molecules
B. The VSEPR Model
Three Pairs of Electrons
• BF3
– 120o – trigonal planar
Section 12.4
Structure of Molecules
B. The VSEPR Model
Four Pairs of Electrons
• CH4
– 120o – tetrahedral
Section 12.4
Structure of Molecules
The VSEPR Model
Section 12.4
The VSEPR Model
Structure of Molecules
Section 12.4
Structure of Molecules
C. Molecules with Double Bonds
When using VSEPR model to predict molecular
geometry of a molecule
• a double bond is counted the same as a single electron pair
Section 12.4
Structure of Molecules
Practice – Draw the Lewis Dot and Determine the Shape
• CL2
Virtual Lab
LQHS
Section 12.4
Structure of Molecules
Practice – Draw the Lewis Dot and Determine the Shape
• SiCl4
Section 12.4
Structure of Molecules
Practice – Draw the Lewis Dot and Determine the Shape
• H2S
Section 12.4
Structure of Molecules
Practice – Draw the Lewis Dot and Determine the Shape
• AsH3
Section 12.4
Structure of Molecules
Practice – Draw the Lewis Dot and Determine the Shape
• BF3