Properties of Liquids and Solids

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.

Intermolecular Forces

Types of IMF London Dispersion Forces View animation online.

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

Types of IMF Hydrogen Bonding

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

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

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

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

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

Types of Solids Ionic (NaCl) Metallic

Types of Solids Covalent Molecular Covalent Network Amorphous (H2O) (SiO2 - quartz) Amorphous (SiO2 - glass)

Types of Solids

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.

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

Phase Changes

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

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

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

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

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

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

Heating and Cooling curve

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 1°C -

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

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

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

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

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. S L G Temperature Pressure Triple Point

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

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

Phase Change of Water

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