II. Forces of Attraction

Water The only substance we are familiar with as a solid, liquid and gas.

A. Molecular Forces Intramolecular Ionic Bonds Covalent Bonds Metallic Bonds Within Particles Intermolecular Dispersion Forces Dipole-dipole Forces Hydrogen Bonds Between Particles

B. Dispersion Forces Creation of temporary dipoles Electron clouds in close contact repel Temporary dipoles (positive and negative regions) Attraction increases with particle size Also called London or Van der Waals forces

C. Dipole-dipole forces Permanent dipoles Oppositely charged regions of polar molecules Adjacent molecules orient to each other

D. Hydrogen Bonds Specialized type of dipole-dipole force H + O, F or N H2O – most famous example Responsible for water’s unique properties Click for animation on all IM forces Web or Real video

III. Liquids and Solids Liquids Fixed volume Variable shape – adjusts to container Practically incompressible Fluid – can flow and diffuse

Hydraulics

B. Viscosity Resistance of a liquid to flow Type of intermolecular forces Size and shape of particles Temperature

Multi-viscosity motor oil

Surface tension

Surfactants – lower surface tension – basis of detergents

Cohesion

Adhesion Water (L) and mercury (R) Adhesion > cohesion; cohesion > adhesion

Capillary Action (adhesion)

III. Solids Firewalk, Agia Eleni, Greece Click on picture

A. Structure Particles in constant motion Strong attractive forces Vibrations around fixed locations More order than in fluids

B. Density Most solids will sink in their own liquids (more dense) Main exception – H2O Rigid crystal structure takes more space

C. Crystalline Solids Orderly, geometric structure Crystal lattice – location of particles on a framework Unit cell – smallest intact part of a whole crystal (You will not be tested on the unit cell types, p. 421)

4. Categories of crystalline solids Atomic – group 18 at low temps Molecular – covalent single bonds Covalent network – repeating structure; diamond, quartz, etc. Ionic – metal + nonmetal Metallic

5. Amorphous solids No regular, repeating pattern Often product of rapid cooling Glass, rubber, plastic

IV. Phase Changes

A. Phase Changes Requiring Energy

Key Terms/Points: Melting point – exact for crystalline solids, approximate for amorphous solids Aluminum – 660.4 O C Cocoa butter – 32-34 OC

2. Vaporization – change from liquid to gas Evaporation – any temperature, surface only Vapor Pressure – pressure of a vapor on top of a liquid Boiling Point – VP inside a liquid equals external VP.

3. Sublimation Direct transition from solid to gas

B. Phase Changes Releasing Energy 1. Freezing – releases energy to a point where bonds can re-form.

2. Condensation Change from gas to liquid

3. Deposition Change from gas to solid

C. Phase Diagram A graph of pressure vs. temperature that shows which a phase a substance exists in under different conditions of temperature and pressure.

Pressure Cooker & Autoclave Raises temperature by raising pressure

Carbon Dioxide tank cars

Phase Diagram for Carbon

Diamond Making Machine