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Unformatted text preview: Chapter 11 Intermolecular Forces, Liquids, and Solids Chapter The fundamental difference between The states of matter is the distance between particles. particles. Because particles in the solid and liquid states Because are closer together, they are called condensed phases. phases The state of a substance at a given The temperature and pressure depends on two opposing forces: opposing Kinetic energy of the particles Strength of attractions between the particles Forces between molecules Forces
van der Waals Forces: Dipole-dipole interactions, van Hydrogen bonding, London dispersion forces Hydrogen A fourth type of force, ion-dipole interactions are an fourth important force in solutions of ions. important The strength of these forces are what make it The possible for ionic substances to dissolve in polar solvents. solvents. Dipole-Dipole Interactions: Molecules with permanent Dipole-Dipole dipoles are attracted to each other. dipoles Dipole-Dipole Interactions Dipole-Dipole The more polar the molecule the higher its boiling point. London Dispersion Forces London Induced dipole A nearby He atom would have a dipole induced in nearby induced it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1. London dispersion forces (or dispersion forces) are attractions betweenan instantaneous dipole and attractions instantaneous an induced dipole. an induced London Dispersion Forces London
These forces are present in all molecules, whether they These all are polar or nonpolar. are The tendency of an electron cloud to distort in this way The is called polarizability. polarizability Factors Affecting London Forces: Molecule shape Factors affects the strength of dispersion forces: long, skinny molecules (like n-pentane tend to have stronger -pentane dispersion forces than short, fat ones (like neopentane). neopentane). This is due to the increased surface area in n-pentane. This -pentane. Factors Affecting London Forces: The strength of dispersion forces increases with increased molecular weight. Larger atoms have larger electron clouds, which are easier to polarize. which Dipole-Dipole vs Dispersion Forces? Dipole-Dipole If two molecules are of comparable If size and shape, dipole-dipole interactions will likely be the dominating force. dominating If one molecule is much larger than If another, dispersion forces will likely determine its physical properties. determine Hydrogen bonding? Hydrogen The nonpolar series (SnH4 to CH4) follow the expected trend. The polar series follows the trend from H2Te through H2S, but S, water is an anomaly. Hydrogen Bonding: The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine (Strong attraction for e-). Also, when hydrogen is bonded to one of those attraction ). very electronegative elements, the hydrogen nucleus is exposed. very Summary of Intermolecular Forces Summary Intermolecular forces & physical properties Intermolecular
The strength of the attractions The between particles can greatly affect the properties of a substance or solution. Viscosity is the resistance Viscosity of a liquid to flow. of It is related to the ease with which It molecules can move past each other. Viscosity increases with stronger intermolecular forces and decreases with higher temperature. decreases Phase Changes Phase Energy Changes and Changes of State Energy Heat of Fusion: Energy required to change a solid at its melting point to a liquid. Heat of Vaporization: Heat Energy required to change a liquid at its boiling point to a gas. point Energy Changes and Changes of State Energy The heat added to the system at the melting and The boiling points goes into pulling the molecules farther apart from each other. farther The temperature of the substance does not rise The during the phase change. during ...
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