Textbook Question
Determine the kinds of intermolecular forces that are present in each element or compound. c. CH3OH
Ch.11 - Liquids, Solids & Intermolecular Forces
Chapter 11, Problem 41a,b
In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. a. CH3OH or CH3SH b. CH3OCH3 or CH3CH2OH
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Identify the types of intermolecular forces present in each compound. For example, CH3OH has hydrogen bonding, while CH3SH has dipole-dipole interactions and London dispersion forces.
Recall that hydrogen bonding is generally stronger than dipole-dipole interactions and London dispersion forces, leading to higher boiling points.
Compare the molecular structures of CH3OH and CH3SH. Note that CH3OH can form hydrogen bonds due to the presence of an -OH group, whereas CH3SH cannot form hydrogen bonds as effectively because it has an -SH group.
For the second pair, CH3OCH3 (dimethyl ether) has dipole-dipole interactions and London dispersion forces, while CH3CH2OH (ethanol) can form hydrogen bonds due to its -OH group.
Conclude that compounds with hydrogen bonding, such as CH3OH and CH3CH2OH, typically have higher boiling points than those with only dipole-dipole interactions and London dispersion forces.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrogen Bonding
Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine. This interaction significantly increases the boiling point of compounds because more energy is required to break these bonds during the phase transition from liquid to gas.
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Hydrogenation Reactions
Molecular Polarity
Molecular polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have an uneven distribution of charge, tend to have higher boiling points than nonpolar molecules due to stronger intermolecular forces, such as dipole-dipole interactions and hydrogen bonding.
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Molecular Weight
Molecular weight, or molar mass, is the mass of a molecule calculated by adding the atomic masses of its constituent atoms. Generally, compounds with higher molecular weights have higher boiling points due to increased van der Waals forces, which are the weak attractions between molecules that become more significant as the size of the molecules increases.
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