Ch. 4: “The Structure of Matter”
Section 1: “Compounds & Molecules”
SR 4.1, pg. 114, #1-8
1. Classify the following substances as
mixtures or compounds.
a. air
b. CO
c. SnF2
d. pure water
a. mixture
b. compound
c. compound
d. compound
2. Explain why silver iodide, AgI, a compound used in
photography, has a much higher melting point than vanillin,
C8H8O3, a sweet smelling compound used in flavorings.
• Silver iodide has a network
structure of positive & negative
ions. Vanillin consists of molecules.
The attraction between particles of
silver iodide is stronger than the
attraction between particles of
vanillin.
3. Draw a ball-&-stick model of boron trifluoride, BF3, molecule. In
this molecule, a boron atom is attached to the 3 fluorine atoms.
Each F-B-F bond angle is 120⁰, & all B-F bonds are the same length.
4. Predict which molecules have a greater attraction for each
other, C3H8O molecules in liquid rubbing alcohol or CH4
molecules in methane gas.
• Molecules in a liquid, such as
C3H8O, have a greater attraction
for each other because they are
closer together & are moving
more slowly than the molecules
in a gas, such as CH4.
5. Explain why glass, which is made mainly of SiO2, is often used
to make cookware. (Hint: What properties does SiO2 have
because of its structure?)
• SiO2 has a network structure,
resulting in a high melting point.
Therefore, it does not melt when
heated to high cooking
temperatures.
6. Predict whether a compound is made of molecules
that melt at -77.7⁰C is a solid, liquid, or gas at room
temperature.
• Because of its low melting point,
it is probably a gas at room
temperature.
7. Creative Thinking
• A picometer (pm) is equal to 1 x 10-12 m. O-H
bond lengths in water are 95.8 pm, while S-H
bond lengths in dihydrogen sulfide are 135 pm.
Why are S-H bond lengths longer than O-H bond
lengths? (Hint: Which is larger, a sulfur atom or
oxygen atom?)
• Sulfur atoms are larger than oxygen atoms by one
electron energy level. Their valence electrons are
farther from the nucleus, so the nucleus-tonucleus distance is greater.