Chapter 13: States of Matter

1. Table of Contents Chapter 13: States of Matter Basics: Solids, Liquids, Gases

2. Practical Applications • Intermolecular forces can be used to explain properties of solids, liquids and gases Practical Applications - GASES • Vapor: the gas phase of a substance that is usually a liquid at room temperature (as water is)

3. Practical Applications - GASES • Vapor Pressure • The pressure of the gas “supported” over a liquid • Indirectly related to the intermolecular forces within a liquid • Higher intermolecular forces → more energy needed to escape → lower vapor pressures → higher boiling points • Volatility • Liquids with high vapor pressures (evaporate easier) are volatile

4. States of Matter: Basic Concepts Liquids • Particles are in constant motion • Fluidity is the ability to flow. • Gases and liquids are classified as fluids because they can flow. • A liquid diffuses more slowly than a gas at the same temperature (Why?) • Because intermolecular attractions interfere with the flow.

5. Practical Applications - LIQUIDS • Adhesive Forces • Substances bind to surfaces • Causes a meniscus • Cohesive Forces • Binds molecules to each other

6. States of Matter: Basic Concepts LIQUIDS • Viscosity: the resistance of a liquid to flow. • ↑ Temperature = ↓Viscosity • Why? • With the increase in temperature, there is an increase in the average kinetic energy (velocity) of the molecules.

7. States of Matter: Basic Concepts LIQUIDS • Surface tension: the inward pull by particles under the surface. • The energy required to increase the surface area of a liquid • Particles in the middle of the liquid can be attracted to particles above them, below them, and to either side. • The overall attractive force is pulling down on particles at the surface.

8. States of Matter: Basic Concepts Solids • Particles are in constant motion. • For a substance to be a solid rather than a liquid at a given temperature, there must be stronger ________ _________ acting between particles in the solid. attractive forces

9. States of Matter: Basic Concepts Density of solids • REMINDER: These forces limit the motion of the particles • vibrations around fixed locations • More order - not classified as fluids • Dense: particles are closely packed • Without looking at your notes, give a detailed description of each phase

10. States of Matter: Basic Concepts • Crystalline solids: solids which have a well defined arrangement • Flat surfaces - Definite angles • A lattice: the 3D structure of a crystalline solid.

11. States of Matter: Basic Concepts • Crystalline solids: solids which have a well defined arrangement • A unit cell: the smallest arrangement of connected points that can be repeated to form the lattice.

12. States of Matter: Basic Concepts • Crystalline solids: solids which have a well defined arrangement • Crystals: the individual pieces of a crystalline solid. • ex) quartz, diamond

13. Crystalline solids • Crystalline solids can be classified into 5 categories based on the types of particles they contain:

14. States of Matter: Basic Concepts • Amporphous solids: No orderly structure • Lack of well defined faces or angles • ex) rubber, glass Tell the difference between crystalline and amorphous solids

15. States of Matter: Basic Concepts • Remember: • Ionic solids dissolve in water, conduct electricity and heat • Covalent/Amorphous solids do not dissolve in water, conduct electricity and heat