Chapter 12: Problem 82
What is the strongest type of intermolecular attraction that exists in each of the following liquids? (a) \(\mathrm{C}_{8} \mathrm{H}_{18}\) (b) \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{Cl}\) (c) HCOOH (d) \(\mathrm{C}_{2} \mathrm{H}_{5}-\mathrm{O}-\mathrm{C}_{2} \mathrm{H}_{5}\)
Short Answer
Expert verified
(a) London dispersion, (b) Dipole-dipole, (c) Hydrogen bonding, (d) Dipole-dipole.
Step by step solution
01
Identify the Molecular Structures
Examine the molecular structures of each compound to determine the types of atoms and bonds present, which will help identify potential dipole moments or hydrogen bonding capabilities.- (a) \( \mathrm{C}_{8} \mathrm{H}_{18} \) is octane, a hydrocarbon with nonpolar characteristics.- (b) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-Cl} \) is ethyl chloride, involves a polar C-Cl bond.- (c) HCOOH, known as formic acid, involves an \(-\mathrm{COOH}\) carboxylic acid group capable of hydrogen bonding.- (d) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-O-}\mathrm{C}_{2} \mathrm{H}_{5} \) is diethyl ether, containing an \(-\mathrm{O}-\) oxygen linking two ethyl groups, able to form dipole-dipole interactions.
02
Determine the Type of Intermolecular Forces Present
For each compound, we now determine the strongest type of intermolecular force based on the presence of polar bonds and hydrogen bonding.- (a) \( \mathrm{C}_{8} \mathrm{H}_{18} \): The molecule is nonpolar, leading to London dispersion forces as the strongest intermolecular force.- (b) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-Cl} \): The C-Cl bond is polar, making dipole-dipole interactions the strongest force.- (c) HCOOH: The presence of \(-\mathrm{OH}\) and \(\mathrm{C=O} \) bonds enables hydrogen bonding as the strongest force.- (d) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-O-}\mathrm{C}_{2} \mathrm{H}_{5} \): Contains polar bonds fostering dipole-dipole interactions.
03
Confirm the Strongest Force for Each Compound
Confirming our identification:- (a) As \( \mathrm{C}_{8} \mathrm{H}_{18} \) is nonpolar, its strongest force is London dispersion.- (b) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-Cl} \), being polar, strongest is dipole-dipole.- (c) HCOOH forms significant hydrogen bonds, establishing hydrogen bonds as the strongest.- (d) \( \mathrm{C}_{2} \mathrm{H}_{5}\text{-O-}\mathrm{C}_{2} \mathrm{H}_{5} \), with dipole-dipole interactions as its strongest force.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molecular Structure
Understanding the molecular structure of a compound is the first step in predicting its chemical properties, including intermolecular forces. The molecular structure refers to the arrangement of atoms within a molecule, influencing the type of bonds present and how these molecules interact with each other in a substance.
In the case of octane (\( \mathrm{C}_{8} \mathrm{H}_{18} \)), the molecular structure consists of long chains of carbon and hydrogen atoms. This arrangement creates a nonpolar molecule since there is no difference in electronegativity between C and H that could induce a polarity.
On the other hand, ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)) demonstrates a simple molecular structure where a chlorine atom is bonded to an ethyl group. The electronegative chlorine atom induces polarity in the molecule, illustrating how molecular structure directly affects chemical properties.
For formic acid (HCOOH), the \( \text{-COOH} \) group present significantly influences its molecular structure, permitting hydrogen bonding. Understanding such molecular structures is essential in determining the types of intermolecular forces present.
In the case of octane (\( \mathrm{C}_{8} \mathrm{H}_{18} \)), the molecular structure consists of long chains of carbon and hydrogen atoms. This arrangement creates a nonpolar molecule since there is no difference in electronegativity between C and H that could induce a polarity.
On the other hand, ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)) demonstrates a simple molecular structure where a chlorine atom is bonded to an ethyl group. The electronegative chlorine atom induces polarity in the molecule, illustrating how molecular structure directly affects chemical properties.
For formic acid (HCOOH), the \( \text{-COOH} \) group present significantly influences its molecular structure, permitting hydrogen bonding. Understanding such molecular structures is essential in determining the types of intermolecular forces present.
Polar Bonds
Polar bonds occur when two atoms have a difference in electronegativity, causing a partial positive and negative charge across the bond. This polarity affects how molecules interact with one another, specifically through dipole-dipole interactions.
In ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)), the carbon-chlorine (\( \text{C-Cl} \)) bond is polar due to chlorine's higher electronegativity compared to carbon. This creates an imbalance of charge distribution, resulting in a net dipole moment.
Similarly, diethyl ether (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-O-} \mathrm{C}_{2} \mathrm{H}_{5} \)) features an oxygen atom, which is more electronegative than the carbon atoms it connects. This leads to polar bonds that contribute to intermolecular dipole-dipole interactions.
With polar bonds, the molecular structure determines the extent of the molecule's polarity, which in turn dictates the type and strength of intermolecular forces possible.
In ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)), the carbon-chlorine (\( \text{C-Cl} \)) bond is polar due to chlorine's higher electronegativity compared to carbon. This creates an imbalance of charge distribution, resulting in a net dipole moment.
Similarly, diethyl ether (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-O-} \mathrm{C}_{2} \mathrm{H}_{5} \)) features an oxygen atom, which is more electronegative than the carbon atoms it connects. This leads to polar bonds that contribute to intermolecular dipole-dipole interactions.
With polar bonds, the molecular structure determines the extent of the molecule's polarity, which in turn dictates the type and strength of intermolecular forces possible.
Hydrogen Bonding
Hydrogen bonding is a particularly strong type of dipole-dipole interaction occurring in molecules where hydrogen is covalently bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine. This creates a significant positive charge on the hydrogen, which strongly attracts the lone pairs on adjacent electronegative atoms.
Formic acid (HCOOH) is a classic example where hydrogen bonding plays a pivotal role. The presence of the \( \text{-OH} \) group allows hydrogen atoms to engage in hydrogen bonding with oxygen from another formic acid molecule. This is due to the strong difference in electronegativity between oxygen and hydrogen, resulting in formic acid's hydrogen bonds being its strongest type of intermolecular force.
Hydrogen bonding significantly influences the boiling and melting points of compounds, as the energy required to break these strong interactions is considerably higher than for other types of intermolecular forces.
Formic acid (HCOOH) is a classic example where hydrogen bonding plays a pivotal role. The presence of the \( \text{-OH} \) group allows hydrogen atoms to engage in hydrogen bonding with oxygen from another formic acid molecule. This is due to the strong difference in electronegativity between oxygen and hydrogen, resulting in formic acid's hydrogen bonds being its strongest type of intermolecular force.
Hydrogen bonding significantly influences the boiling and melting points of compounds, as the energy required to break these strong interactions is considerably higher than for other types of intermolecular forces.
Dipole-Dipole Interactions
Dipole-dipole interactions are the forces that occur between polar molecules, where the positive end of one molecule is attracted to the negative end of another. These interactions are stronger than London dispersion forces but generally weaker than hydrogen bonding.
Ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)) is an example where the significant polarity of the \( \text{C-Cl} \) bond leads to dipole-dipole interactions being the principal intermolecular force. The polar nature of this bond causes molecules to align themselves with the positively charged end facing the negatively charged end of another molecule.
Similarly, in diethyl ether (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-O-} \mathrm{C}_{2} \mathrm{H}_{5} \)), the oxygen atom creates a dipole as it is more electronegative than carbon atoms. These dipole-dipole interactions contribute to the compound's specific boiling point and solubility characteristics. Understanding these interactions helps predict and explain the physical behaviors of substances under various conditions.
Ethyl chloride (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-Cl} \)) is an example where the significant polarity of the \( \text{C-Cl} \) bond leads to dipole-dipole interactions being the principal intermolecular force. The polar nature of this bond causes molecules to align themselves with the positively charged end facing the negatively charged end of another molecule.
Similarly, in diethyl ether (\( \mathrm{C}_{2} \mathrm{H}_{5} \text{-O-} \mathrm{C}_{2} \mathrm{H}_{5} \)), the oxygen atom creates a dipole as it is more electronegative than carbon atoms. These dipole-dipole interactions contribute to the compound's specific boiling point and solubility characteristics. Understanding these interactions helps predict and explain the physical behaviors of substances under various conditions.
