1. Phases of Matter

4. Solids matter is arranged in a regular, rigid pattern definite shape and volume crystalline structure

5. Liquids particles not held as tightly together able to move past one another (flow) definite volume, no definite shape

6. Gases Minimal attractive forces holding particles together No definite shape or volume (takes the shape and volume of a container)

7. Phase Changes all phase changes are accompanied with either a loss or gain of energy an element, compound, or mixture can exist as a solid, liquid, or gas (s, l, g)

8. Endothermic Changes Phase changes that require the gain of heat Examples 1. melting/fusion- solid substance becomes liquid 2. evaporation/boiling/vaporization- liquid substance becomes gas 3. sublimation- solid substance changes directly to a gas

10. Exothermic Reactions all of these phase changes require the loss or release of energy Examples 1. freezing/solidification – liquid substance becomes solid 2. condensation – gaseous substance becomes liquid 3. deposition – gaseous substance turns directly into a solid

12. Phases In Detail Solids

13. True solids have a crystalline structure 1. Crystals are arranged in repeated geometric patterns 2. Example: ice (strong intermolecular attraction)

14. Pseudosolids lack crystalline structure 1. Examples: glass, some plastics 2. These are supercooled liquids

15. Sublimation When a solid changes directly into a gas by the addition of heat Substances that sublime have high vapor pressure (lots of gas hovering over the solid) Low intermolecular forces of attraction (particles break apart easily) Examples: 1. Dry ice (frozen carbon dioxide) CO 2 (s) 2. Solid iodine I 2 (s) 3. mothballs