Activity #10.5: Polarity of Molecules
AP Chemistry
What effect does the shape or geometry of the molecule have on molecular polarity?
Why?
Why are oil and water mixtures immiscible? What causes sugar to dissolve in water? The
geometry of a molecule has an effect on physical properties such as solubility. How can the
molecular geometry be used to predict properties?
Model 1
Non Polar Molecule
CH4
Polar Molecules
NH3
H2O
# Bonding
electron pairs
# Lone pairs
of electrons
on central
atom
AB
designation
E
1. Complete the table in Model 1. Determine the # of Bonding electron pairs and # of lone pairs
of electrons for each species. Compare your answers with your team members.
E
2. Identify the AB type for each molecule and check with your team members.
E
3. a
b.
I
What is the number of lone pairs of e- in the non polar molecule.
What is the number of lone pairs of e- in the polar molecules
4. Write a cohesive sentence that explains the relationship between lone pairs and polarity of a
molecule.
5. Draw and picture of CH2H2. Determine the number of bonding electron pairs and lone pairs of
electrons. Is this a polar molecule? Explain.
Model 2
Non Polar Molecules
Polar Molecules
Key
= Carbon ( EN =2.5)
= Chlorine (EN= 2.7)
= Hydrogen (EN = 2.3)
E
6. Write the formulas and names for the non-polar molecules.
E
7. Write the formulas and names for the polar molecules.
E
8. What do the non-polar molecules have in common?
E
9. What do the polar molecules have in common?
I
10. By observing Model 2, what is the main reason a non-polar molecule to exhibit polarity?
Be specific. Compare your answer to your team members and reach a consensus.
E
11. Determine the ΔEN for each of the bonds and write the results on the model.
12. Look at Model 2 and write down any trends in polar and non-polar molecules and ΔEN
E
I
13. Using Models 1 and 2. What are THREE factors that determine if a molecule is polar.
a.
b.
c.
I
14. Using Models 1 and 2. What are THREE key characteristics of a non-polar molecule?
a.
b.
c.
15. Using the concepts developed on whether a molecule is polar or non-polar, fill in the table
below.
A
Geometry
ABE Form
Non-Polar or Polar
Extension Questions:
1. Write the Lewis Dot Structure for the following compounds. Predict the molecular
geometry, AB form, and molecular polarity.
a. NO3-
b. SO2
c. SF4
d. XeF4
e. PCl5
HSPI Activity #10.5: Polarity of Molecules Teacher Guide
AP Chemistry
 Objectives
o Students will distinguish between polar bonds and polar molecules.
o Students will be able to compare and contrast polar and non polar molecules by
o
utilizing EN differences of bonds in conjunction with molecular shape and
symmetry.
Students will be able to discover that lone pairs of electrons can have an effect on
molecular polarity
 Prerequisites
o
o
o
o
Students should be proficient in drawing Lewis dot structures for molecules. .
Students should be able to predict molecular shape, AB form and bond angles.
Students should be able to define polar and nonpolar bonds.
Students need to determine EN differences of bonds and use the calculated value to
predict the type of bonding.
 Assessment Questions
1. Which of the following is the correct Lewis structure for SOCl2?
a)
d)
b)
e)
c)
2. Which one of the following molecules is a polar molecule?
a)
c)
b)
d)
3. If a molecule has an AB3 form, draw the possible Lewis structures, identify the AB format,
molecular shape and explain molecular polarities ( if all bonded atoms are the same species)
 Teacher Tips
1.
Molecular model kits should be available for student use. The models aid in
determining polarity of the molecule
2. It is recommended that students be given opportunities to practice a variety of
molecules.
 Targeted Responses
Activity #10.5: Polarity of Molecules
AP Chemistry
What effect does the shape or geometry of the molecule have on molecular polarity?
Why?
Why are oil and water mixtures immiscible? What causes sugar to dissolve in water? The
geometry of a molecule has an effect on physical properties such as solubility. How can the
molecular geometry be used to predict properties?
Model 1
Non Polar Molecule
# Bonding
electron pairs
# Lone pairs
of electrons
on central
atom
AB
designation
Polar Molecules
CH4
4
NH3
3
H2O
2
0
1
2
AB4
AB3E
AB2E2
E
1. Complete the table in Model 1. Determine the # of Bonding electron pairs and # of lone pairs
of electrons for each species. Compare your answers with your team members.
E
2. Identify the AB type for each molecule and check with your team members.
E
3. a. What is the number of lone pairs of e- in the non polar molecule. 0
b.
What is the number of lone pairs of e- in the polar molecules. >0 1 and 2
4. Write a cohesive sentence that explains the relationship between lone pairs and polarity of a
molecule. When a molecule has 1 or more lone pairs, the molecule is polar.
I
5. Draw and picture of CH2H2. Determine the number of bonding electron pairs and lone pairs of
electrons. Is this a polar molecule? Explain.
Model 2
Non Polar Molecules
Polar Molecules
ΔEN = 0.4
C-H: ΔEN = 0.4
C-Cl: ΔEN = 0.5
ΔEN = 0.5
C-H: ΔEN = 0.4
C-Cl: ΔEN = 0.5
C-H: ΔEN = 0.4
C-Cl: ΔEN = 0.5
Key
= Carbon ( EN =2.5)
= Chlorine (EN= 3.0)
= Hydrogen (EN = 2.1)
E
6. Write the formulas and names for the non-polar molecules.CH4
CCl4
E
7. Write the formulas and names for the polar molecules.
CH3Cl
CH2Cl2
CHCl3
E
8. What do the non-polar molecules have in common? Same type of atoms attached to
the central atom (carbon)
E
9. What do the polar molecules have in common? Different types of atoms attached to
the central carbon ( Cl, H)
I
10. By observing Model 2, what is the main reason a non-polar molecule to exhibit polarity?
Be specific. Compare your answer to your team members and reach a consensus.
The main reason a non-polar molecule exhibits polarity is due to different types of
atoms ( with different EN values) attached to the central atom.
E
11. Determine the ΔEN for each of the bonds and write the results on the model.
12. Look at Model 2 and write down any trends in polar and non-polar molecules and ΔEN
As the ΔEN increases between the central atom and the surrounding atoms, the
greater the possibility the molecule is polar.
E
I
13. Using Models 1 and 2. What are THREE factors that determine if a molecule is polar.
a. If the central atom is surrounded by different types of atoms that may have
different EN values
b. If the molecule is symmetrical around the central atoms
c. If there are lone electron pairs
I
14. Using Models 1 and 2. What are THREE key characteristics of a non-polar molecule?
a. Atoms attached to the central atom are the same with the same EN values.
b.The molecule is symmetrical
c. There are no lone electron pairs.
15. Using the concepts developed on whether a molecule is polar or non-polar, fill in the table
below.
A
Geometry
ABE Form
Non-Polar or Polar
AB5
Non- Polar
AB4 E
Polar
AB3 E2
Polar
AB5 E
Polar
AB4 E2
Non- Polar
AB2 E3
Non- Polar
Extension Questions:
1. Write the Lewis Dot Structure for the following compounds. Predict the molecular
geometry, AB form, and molecular polarity.
a. NO3-
Trigonal planar
AB3
Ion
Resonance
Bent
AB2E
Polar
Resonance
See Saw
AB4E
Polar
ABrE2
Non-Polar
b. SO2
c. SF4
d. XeF4
Square Planar
e. PCl5
Trigonal Bipyramidal
AB5
Non-Polar
HSPI Activity #10.5: Polarity of Molecules Teacher Guide
AP Chemistry
 Objectives
o Students will distinguish between polar bonds and polar molecules.
o Students will be able to compare and contrast polar and non polar molecules by
o
utilizing EN differences of bonds in conjunction with molecular shape and
symmetry.
Students will be able to discover that lone pairs of electrons can have an effect on
molecular polarity
 Prerequisites
o
o
o
o
Students should be proficient in drawing Lewis dot structures for molecules. .
Students should be able to predict molecular shape, AB form and bond angles.
Students should be able to define polar and nonpolar bonds.
Students need to determine EN differences of bonds and use the calculated value to
predict the type of bonding.
 Assessment Questions
1. Which of the following is the correct Lewis structure for SOCl2? B
a)
d)
b)
e)
c)
2. Which one of the following molecules is a polar molecule? B
a)
c)
b)
d)
3. If a molecule has an AB3 form, draw the possible Lewis structures, identify the AB format,
molecular shape and explain molecular polarities ( if all bonded atoms are the same species)
Possible AB Forms:
AB3 ( Trigonal Planar – Non-Polar- no lone pairs, symmetrical )
AB3E ( Trigonal Pyramidal – Polar- 1 lone pair, asymmetrical)
AB3E2 (T-Shape- Polar- 2 lone pairs, asymmetrical)
AB3E3 (T-Shape- Polar- 3 lone pairs, asymmetrical)