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Intermolecular Forces Intermolecular Forces: weaker interactions that occur between molecules. These are collectively known as Van der Waals forces. Intramolecular Forces: Do not confuse Inter with Intra! Intramolecular forces are how we describe bonding between atoms.

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Intermolecular Forces

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Types of IMF London Dispersion Forces View animation online.animation

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Types of IMF Dipole-Dipole Forces + + - - View animation online.animation

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Types of IMF Hydrogen Bonding

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Liquids vs. Solids IMF Strength Fluid Density Compressible Diffusion LIQUIDS Stronger than in gases Y high N slower than in gases SOLIDS Very strong N high N extremely slow

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Liquid Properties Surface Tension attractive force between particles in a liquid that minimizes surface area

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Liquid Properties Capillary Action attractive force between the surface of a liquid and the surface of a solid watermercury

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Viscosity: Resistance to flow (molecules with large intermolecular forces). Liquid Properties

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Types of Solids Crystalline - repeating geometric pattern covalent network metallic ionic covalent molecular Amorphous - no geometric pattern decreasing m.p.

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Types of Solids Ionic (NaCl) Metallic

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Types of Solids Covalent Molecular (H 2 O) Covalent Network (SiO 2 - quartz) Amorphous (SiO 2 - glass)

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Types of Solids

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Types of Solids: Metals The electron sea model for metals postulates a regular array of cations in a "sea" of valence electrons. (a) Representation of an alkali metal (Group 1A) with one valence electron. (b) Representation of an alkaline earth metal (Group 2A) with two valence electrons.

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Types of Solids: Metals Alloy: A substance that contains a mixture of elements and has metallic properties Substitutional Alloy (a): some of the host metal atoms are replaced with atoms similar size metal atom Interstial Alloy (b): some of holes between the metal atoms are filled with smaller atoms

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Phase Changes

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Evaporation Evaporation molecules at the surface gain enough energy to overcome IMF Volatility Volatility measure of evaporation rate depends on temp & IMF

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Phase Changes Equilibrium Equilibrium trapped molecules reach a balance between evaporation & condensation

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Phase Changes Vapor Pressure Vapor Pressure pressure of vapor above a liquid at equilibrium IMFv.p.tempv.p. depends on temp & IMF directly related to volatility temp v.p.

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Phase Changes Boiling Point temp at which v.p. of liquid equals external pressure IMFb.p.P atm b.p. depends on P atm & IMF Normal B.P. - b.p. at 1 atm

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Which has a higher m.p.? polar or nonpolar? covalent or ionic? Phase Changes Melting Point equal to freezing point polar ionic IMFm.p.

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Phase Changes Sublimation solid gas v.p. of solid equals external pressure EX: dry ice, mothballs, solid air fresheners

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Heating and Cooling curve

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Heating Curves Temperature Change change in KE (molecular motion) depends on heat capacity Heat Capacity energy required to raise the temp of 1 gram of a substance by 1C -

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Heating Curves Phase Change change in PE (molecular arrangement) temp remains constant Heat of Fusion ( H fus ) energy required to melt 1 gram of a substance at its m.p.

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Heating Curves Heat of Vaporization ( H vap ) energy required to boil 1 gram of a substance at its b.p. usually larger than H fus why? EX: sweating, steam burns, the drinking bird

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Temperature Pressure Phase Diagrams We know that different compounds can have different phases. These phases depend on the temperature and pressure of the substance. We can then use that information to create a diagram of the different phases called a PHASE DIAGRAM.

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Looking at Phase Diagrams The boundaries between phases occur at phase changes (ie. melting, freezing, vaporizing, etc.) A - melting, freezing B - vaporization, condensation C - sublimation, deposition S L G Temperature Pressure A B C

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S L G Temperature Pressure Looking at Phase Diagrams The triple point is where the boundaries converge at one point and all three phases are present at the same time. Triple Point

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S L G Temperature Pressure Looking at Phase Diagrams Critical Point The critical point is the point at which the distinction between the liquid phase and gas phase ceases to exist.

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S L G Temperature Pressure Determining the Melting Point 1. Find the current pressure 2. Draw a line across the diagram 3. At the boundary between the solid and liquid phase, draw a line down to the temperature 4. Determine the temperature 1 atm

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Phase Change of Water

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Phase Diagrams Each substance or compound has different melting/freezing points, boiling/condensing points, and sublimation/deposition points. Therefore, each substance or compound has a different phase diagram. Carbon