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Ch.12 - Liquids, Solids & Intermolecular Forces
Chapter 12, Problem 40a

Determine the kinds of intermolecular forces that are present in each element or compound. a. HBr

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Identify the type of molecule: HBr is a diatomic molecule consisting of hydrogen (H) and bromine (Br).
Determine the polarity of the molecule: HBr is a polar molecule because there is a significant difference in electronegativity between hydrogen and bromine, causing a dipole moment.
Identify the types of intermolecular forces: Since HBr is polar, it will exhibit dipole-dipole interactions.
Consider the presence of hydrogen bonding: Hydrogen bonding occurs when hydrogen is bonded to highly electronegative atoms like N, O, or F. Since HBr does not meet this criterion, hydrogen bonding is not present.
Account for London dispersion forces: All molecules, including HBr, exhibit London dispersion forces due to temporary dipoles, although these are generally weaker than dipole-dipole interactions in polar molecules.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that influence physical properties such as boiling and melting points. They include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Understanding these forces is crucial for predicting how substances behave in different states and conditions.
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Dipole-Dipole Interactions

Dipole-dipole interactions occur between polar molecules, where positive and negative ends attract each other. In the case of HBr, the molecule has a permanent dipole due to the difference in electronegativity between hydrogen and bromine, leading to significant dipole-dipole interactions that affect its physical properties.
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London Dispersion Forces

London dispersion forces are weak intermolecular forces that arise from temporary shifts in electron density within molecules, creating instantaneous dipoles. These forces are present in all molecules, including nonpolar ones, and become more significant in larger atoms or molecules. In HBr, while dipole-dipole interactions dominate, London dispersion forces still contribute to the overall intermolecular forces.
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