Intermolecular Forces PDF
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This document provides an overview of intermolecular forces, including London dispersion forces, dipole-dipole forces, and hydrogen bonding. It explains how these forces influence physical properties of substances, such as boiling and melting points. It's a useful resource for chemistry students.
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Intermolecular Forces: The Glue Between Molecules Intermolecular forces are the attractive forces that exist between molecules. These forces determine many physical properties of substances, including boiling and melting points, surface tension, and viscosity. Types of Intermolecular Forces 1....
Intermolecular Forces: The Glue Between Molecules Intermolecular forces are the attractive forces that exist between molecules. These forces determine many physical properties of substances, including boiling and melting points, surface tension, and viscosity. Types of Intermolecular Forces 1. London Dispersion Forces (Van der Waals Forces): o Present in all molecules, regardless of polarity. o Caused by temporary fluctuations in electron distribution, creating temporary dipoles. o Strength increases with molecular size and surface area. 2. Dipole-Dipole Forces: o Occur between polar molecules. o Result from the attraction between the positive end of one molecule and the negative end of another. o Stronger than London dispersion forces but weaker than hydrogen bonds. 3. Hydrogen Bonding: o A special type of dipole-dipole force. o Occurs between a hydrogen atom bonded to a highly electronegative atom (N, O, or F) and a lone pair of electrons on another electronegative atom.1 o The strongest of the intermolecular forces. Intermolecular Forces and Physical Properties Boiling Point and Melting Point: Stronger intermolecular forces lead to higher boiling and melting points. This is because more energy is required to overcome the attractive forces between molecules. Surface Tension: Intermolecular forces cause the surface of a liquid to contract, resulting in surface tension. Liquids with stronger intermolecular forces have higher surface tension. Viscosity: Viscosity is a measure of a fluid's resistance to flow. Liquids with stronger intermolecular forces are more viscous. Summary Table Intermolecular Force Description Strength Example London Dispersion All Temporary dipoles Weakest Forces molecules Dipole-Dipole Forces Attraction between polar molecules Moderate HCl, HBr Strong dipole-dipole force involving H2O, NH3, Hydrogen Bonding Strongest H and N, O, or F HF Key Points Intermolecular forces are weaker than intramolecular forces (bonds within molecules). The strength of intermolecular forces affects the physical properties of substances. Understanding intermolecular forces helps explain phenomena like evaporation, condensation, and the behavior of liquids and solids.
