Chemistry Reference
In-Depth Information
As you can see, both carbon dioxide (CO
2
) and methane (CH
4
) are
symmetrical and, therefore, must be non-polar molecules. Water (H
2
O)
and hydrogen chloride (HCl) are asymmetrical and therefore might be polar
molecules. In order to be sure that water and hydrochloric acid are polar
molecules, you must check their electronegativities to be sure that they
have polar covalent bonds, which they do. Water, with its asymmetrical
shape and polar covalent bonds, is the classic of a polar molecule. All tet-
rahedral molecules, because of their symmetrical shape, must be non-po-
lar. All of the diatomic molecules, such as O
2
and H
2
, must be non-polar
because the electronegativity difference between the elements involved
will be zero.
The polarity of molecular compounds is an important influence on the
properties of the substance. For example, you may have heard the expres-
sion “likes dissolve likes,” which is meant to remind us that polar solutes
tend to dissolve in polar solvents, and non-polar solutes tend to dissolve in
non-polar solvents. The polarity of a substance will also affect the intermo-
lecular forces between particles, as you will see in the next chapter.
Lesson 4-6 Review
Use Figure 4-1a and your knowledge of molecular geometry and po-
larity to determine whether or not the following substances are ionic com-
pounds, non-polar molecular compounds, or polar molecular compounds.
1. Li
2
O
3. CBr
4
5. CO
2. I
2
4. NO
6. MgS
Look at the shapes of the molecules in the following figure and deter-
mine if they are symmetrical or asymmetrical.
H
HO
H
N
H
H
O CO
7.
9.
11.
H
Cl
H
C
H
H
Cl C
Cl
Cl
O S
O
8.
10.
12.
