Chemistry Practice
Intermolecular Forces
Spring 2017
A. Define the following terms: 1. Dipole-dipole interactions
2. Hydrogen bonding:
3. London dispersion forces:
B. For each of the following compounds, draw the Lewis structures, indicate the type of bonds in each, draw any dipoles, and identify the main intermolecular force. Nitrogen Gas IMF:_______________
Carbon Tetrachloride IMF:_______________
Hydrogen Sulfide IMF:_______________
Sulfur Monoxide IMF:_______________
Dinitrogen dihydride IMF:_______________
Boron Trihydride IMF:_______________
Chemistry Practice
Methanal IMF:_______________
Intermolecular Forces Ethene IMF:_______________
Spring 2017 Fluoromethane IMF:_______________
C. Answer each questions with complete sentences. 1. Explain why ethyl alcohol (C2H5OH) has a higher boiling point (78.40 C) than methyl alcohol (CH3OH and 64.70 C).
2. Rank the following by from lowest to highest anticipated boiling point: C2H4, CH4, Ne, H3COCH3.
3. Motor oil largely consists of molecules containing long chains of carbon atoms with hydrogen atoms attached to them. Using your knowledge of intermolecular forces, why wouldn’t it be better to use a compound like glycerol. The formula of glycerol is CHOH(CH2OH)2. (Hint: the purpose of motor oil is to coat an engine at high temperatures)
Chemistry Practice
Intermolecular Forces
Spring 2017
Intermolecular Forces Worksheet Answers For each of the following compounds, determine the main intermolecular force. You may find it useful to draw Lewis structures for some of these molecules: 1) 2) 3) 4) 5) 6) 7) 8) 9)
nitrogen – dispersion carbon tetrachloride – dispersion H2S – dipole-dipole forces sulfur monoxide – dipole-dipole forces N2H2 – hydrogen bonding boron trihydride – dispersion CH4O – hydrogen bonding SiH2O – dipole-dipole forces Explain why ethyl alcohol (C2H5OH) has a higher boiling point (78.40 C) than methyl alcohol (CH3OH; 64.70 C). Both molecules contain one O-H bond, which means that they do the same amount of hydrogen bonding. However, ethyl alcohol is a larger molecule, which means that Van der Waals forces are stronger in it, giving it a slightly higher boiling point.
10)
Rank the following by from lowest to highest anticipated boiling point: C2H4, CH4, Ne, H3COCH3. The highest is clearly H3COCH3, as it’s the only polar molecule. The three lowest all experience Van der Waals forces, meaning that the biggest one will have the highest boiling point. Overall, the ranking is Ne (-246.10 C) < CH4 (-161.50 C) < C2H2 (-103.70 C) < H3COCH3 (-23.70 C).
11)
Motor oil largely consists of molecules that consist of long chains of carbon atoms with hydrogen atoms attached to them. Using your knowledge of intermolecular forces, why wouldn’t it be better to use a compound like glycerol. The formula of glycerol is CHOH(CH2OH)2. A casual glance at the structure of glycerol shows that it contains at least one hydrogen bond (and in fact, it contains several) – as a result, we would expect it to have high viscosity. Motor oil, on the other hand, contains only Van der Waals forces, which gives it relatively low viscosity. Because the purpose of motor oil is to quickly coat all surfaces of an engine to keep it from getting too hot, a low viscosity material is better than a high viscosity material.
