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.