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Chapter 11

Chapter 11

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University of Toronto Scarborough
Jamie Donaldson

Chemistry A11 Reactions and Mechanisms Chapter 11 Section 11.1 Climbing and Intermolecular Forces When thermal energy is high relative to intermolecular forces, matter tends to be gaseous. When thermal energy is low relative to intermolecular forces, matter tends to be liquid or solid Section 11.2 Solids, Liquids, and Gases: A Molecular Comparison The densities of the solid and liquid states are much greater than the densities of the gas state Waters solid state (ice) exhibits atypical behaviour, because most solids are slightly denser than their corresponding liquids because the molecules move closer together upon freezing. Liquids are not easily compressed because the molecules or atoms that compose them are already in close contact The molecules in a gas have a great deal of space between them and are easily forced into smaller volume by an increase in external pressure. solids may be crystalline, in which case the atoms or molecules that compose them are arranged in a well ordered three-dimensional array solids may be amorphous, in which case the atoms or moles that compose them have no long-range order we can transform one state of matter to another by changing the temperature, pressure, or both -the most common example of this phenomenon occurs in liquid petroleum, the propane in the tank you buy is under extreme pressure and is therefore a liquid Section 11.3 Intermolecular Forces: The Forces That Hold Condensed States Together The strength of the intermolecular forces between the molecules or atoms that compose a www.notesolution.com substance determines its state. Intermolecular forces originate from the interactions between charges, partial charges, and temporary changes on molecules. Protons and electrons are attracted to each other because their potential energy decreases as they get closer together. Molecules with partial or temporary charges are attracted to each other because their potential energy decreases as they get closer together Intermolecular forces are the result of smaller charges interacting at greater distances The larger the distances between molecules, as well as the smaller charges involved result in weaker forces Dispersion Forces (also called London Forces) are the result of fluctuations in the electron distribution within molecules or atoms -the brief charge separation is known as instantaneous dipole or a temporary dipole The magnitude of the dispersion force depends on how easily the electrons in the atom or molecule can move or polarize in response to an instantaneous dipole, which in turn depends on the size of the electron. A larger electron cloud results in a greater dispersion force because the electrons are held less tightly by the nucleus and therefore polarize more easily -the dispersion force increases with increasing molar mass Molecular shape and other factors must always be considered in determining the magnitude of dispersion forces Dipole-Dipole Forces exist in all molecules that are polar, polar molecules have permanent dipoles that interact with the permanent dipoles of neighbouring molecules. This additional attractive force raises their melting points relative to nonpolar molecules of similar molar mass Miscibility, is the ability to mix without separating into two states Polar moles containing hydrogen atoms bonded to small electronegative atoms (fluorine, oxygen, or nitrogen) exhibit the intermolecular force called hydrogen bonding -the hydrogen bond, a super dipole-dipole force, occurs between the H atom on one molecule and the F, O, or N on it neighbour. www.notesolution.com
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