Lecture 34 Chapter 11 Sections 3 – 6

• Solids

• amorphous

• crystalline

• Phase changes & diagrams

Solids

• In liquids and gases, molecules are free to move continually and randomly.

• In solids, particles are constrained to fixed positions.• Particles can only vibrate and occasionally rotate.• There are four major types (don’t worry about these too

much): – molecular solids– network solids– metallic solids– ionic solids

Forces in Solids

Amorphous vs. Crystalline

• Amorphous solids have fixed shapes, but have irregular internal shapes – no regular structure– plastics– glass (SiO2)– biological membranes

• Crystals have fixed shapes AND regular repeating structures.– NaCl– ice (H2O)– quartz (SiO2)

SiO2 can be either

Sock drawers can be either

Amorphous or crystalline?

54321

Polycarbonate

25%25%25%25% 1. Amorphous

2. Crystalline3. Neither4. Both

Amorphous or crystalline?

54321

Escher

25%25%25%25% 1. Amorphous

2. Crystalline3. Neither4. Both

Amorphous or crystalline?

54321

Escher

25%25%25%25% 1. Amorphous

2. Crystalline3. Neither4. Both

Network Solids of Carbon

Phase Changes

• There are three states– Solid– Liquid– Gas

• A transformation from one state to another is called a phase change

• Each phase change is associated with a change in energy of the system

• Notice that as a phase change occurs, temperature remains constant.

• A substance must completely change phase before the temperature of the system can increase (or decrease).

Heats of Phase Changes

• Molar heat of vaporization, ∆Hvap: the heat needed to vaporize one mole of a substance at its normal boiling point.

• Molar heat of fusion, ∆Hfus: the heat needed to melt one mole of a substance at its normal melting point.

• Molar heat of sublimation, ∆Hsub: the heat needed to vaporize one mole of a substance from the solid phase (skips the liquid phase)

Phase Diagrams

• Illustrate the relationship between phases of matter and the pressure and temperature

• The lines identify the conditions under which two phases exist in equilibrium

• Triple point – point at which all three phases coexist• Critical point – point at which one cannot distinguish

between a gas and a liquid– Beyond this is called a supercritical fluid.

Phase Diagram

Remember: You are done with the homework when you understand it!

Remember: You are done with the homework when you understand it!

Remember: You are done with the homework when you understand it!

Remember: You are done with the homework when you understand it!

Remember: You are done with the homework when you understand it!