A4: Bond Types and Intermolecular Forces (Goals 7-9)
1. Is the following statement true or false? Covalent bonds differ in the way electrons are shared by the bonded
atoms, depending on the kind and number of atoms joined together.
2. Describe how electrons are shared in each type of bond. Write equally or unequally
a. Nonpolar bond Equally
b. polar bond
Unequally
3. Explain how you can use electronegativity values to classify a bond as non-polar, polar covalent, or ionic.
Nonpolar covalent bonds have very small differences in electronegativity (0.0-0.4). Polar bonds have
differences between 0.4 and 2.0. Differences in electronegativity greater than 2.0.
4. Why does the chlorine atom in hydrogen chloride acquire a slightly negative charge?
Chlorine is more electronegative than hydrogen. The electron spends more time near chlorine,
resulting in a slightly negative charge.
5. Circle the letter of each sentence that is true about polar molecules
a. Some regions of a polar molecule are slightly negative and some are slightly positive.
b. A molecule containing a polar bond is always polar.
c. A molecule that has two poles is called a dipolar molecule.
d. When polar molecules are placed in an electric field, they all line up with the same orientation in
relation to the charged plates.
6. Are the following molecules polar or nonpolar (hint: draw them)?
a. H₂O
polar
b. CO₂
nonpolar
c. NH₃
polar
d. CCl4
nonpolar
7. Describe the three types of weak intermolecular attractive forces that hold groups of molecules together. Rank
these forces form weakest to strongest.Dispersion forces are weak and thought to be caused by electron
motion. Dipole interactions are caused by the attraction of the positive and negative poles in a polar
molecule. H-bonding is a strong attraction between a H atom and nearby nonbonding electron pairs.
Dispersion < Dipole < H-bond
8. Not every molecule with polar bonds is polar. Explain this statement using CCl4 as an example.
CCl4 has polar bonds C-Cl have different electronegativities. The overall molecule is symmetrical and
the polarities cancel out resulting in a nonpolar molecule.
9. Depict the hydrogen bonding between two ammonia molecules and between one ammonia molecule and one
water molecule.
Hydrogen
Bond
Hydrogen
Bond
10. Which compound in each pair exhibits the stronger intermolecular hydrogen bonding?
a. H2S, H2O
b. HCl, HF
c. HBr, HCl
d. NH3, H2O
11. Why do compounds with stronger intermolecular attractive forces have higher boiling points than compounds
with weak intermolecular attractive forces?
The attractive forces must be overcome in order to change states. More attractive forces require
more energy (higher temp) to overcome.
12. What must always be true if a covalent bond is to be polar?
For a covalent bond to be polar there must be a difference in electronegativity and asymmetry
13. Explain the trend in the boiling points for the halogens using dispersion forces and polarizability.
The boiling points for halogens increase down a group. This is due to the increasing number of
electrons from F2
I2. More electrons have a higher probability of being polarizable (unevenly
distributed) resulting in stronger dispersion forces.