Ch. 12 – States of Matter I. Intermolecular Forces

A. Definition of IMF  Attractive forces between molecules.  Much weaker than chemical bonds within molecules.  a.k.a. van der Waals forces

C. Johannesson B. Types of IMF

 London Dispersion Forces View animation online.animation

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

B. Types of IMF  Hydrogen Bonding

C. Determining IMF  NCl 3 polar = dispersion, dipole-dipole  CH 4 nonpolar = dispersion  HF H-F bond = dispersion, dipole- dipole, hydrogen bonding

II. Physical Properties Ch Liquids & Solids

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

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

B. Liquid Properties  Capillary Action attractive force between the surface of a liquid and the surface of a solid

B. Liquid Properties  Viscosity Measure of the resistance of a liquid to flow

B. Liquid Properties  Cohesion Force of attraction between identical molecules  Adhesion Force of attraction between different molecules watermercury

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

C. Types of Solids Ionic (NaCl) Metallic

C. Types of Solids Covalent Molecular (H 2 O) Covalent Network (SiO 2 - quartz) Amorphous (SiO 2 - glass)

C. Types of Solids  Allotrope In a covalent network, different forms in the same state Carbon allotropes watermercury

C. Types of Solids  Amorphous Solid No geometric pattern watermercury

Ch Liquids & Solids III. Changes of State

A. Phase Changes

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

A. Phase Changes Kinetic Energy # of Particles Boltzmann Distribution tempvolatilityIMFvolatility

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

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

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

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

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

B. Heating Curves Melting - PE  Solid - KE  Liquid - KE  Boiling - PE  Gas - KE 

B. 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

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

B. Heating Curves  Heat of Vaporization (  H vap ) energy required to boil 1 gram of a substance at its b.p.  EX: sweating, steam burns, the drinking bird

C. Phase Diagrams  Show the phases of a substance at different temps and pressures.

 The following slides… same information, different explanation and examples

Phase Changes

Why do liquids and solids form at all? KMT postulates – A gas is a collection of small particles traveling in straight-line motion and obeying Newton's Laws. – The molecules in a gas occupy no volume. – Collisions between molecules are perfectly elastic no energy is gained or lost during the collision – There are no attractive or repulsive forces between the molecules. – Kinetic energy is proportional to temperature X

What is a phase? Region of matter that is: – chemically uniform – physically distinct – mechanically separable. Often synonymous with (same meaning as) “state of matter”

Changing phases Distinguish liquid vs. solid?

Properties of … Gas phase – Like/unlike soccer players on field Liquid phase – Like/unlike crowd at a rally – Like/unlike gases Solid phase – Like/unlike movie theatre Compare intermolecular interactions – gases vs. liquids vs. solids

Phases of matter Add more energy

Phase change vocabulary A - melting B - freezing C – boiling/ evap D - condensation E - sublimation F - solidification

Phase changes and IMF’s As InterMolecular Forces increase, melting and boiling temperatures _________? (increase or decrease)? Metallic bonding Network covalent bonding Larger sphere, higher melting point

Strength of interactions Which simulation has stronger intermolecular interactions? A or B – How do you know? AB Same temperature

Ranking of intermolecular interactions Water Wood Iron Air Gold Mercury Carbon dioxide Oxygen Gasoline Lead vs. Why?

Why is water special? Periodic trends – Boiling and melting points of hydrides

KMT, energy and phase changes

Total energy

Water phases present?

Heating curves Why are b and d flat?

Boiling vs. melting Which takes more energy? (same mass)

Consider liquid  gas Evaporation removes energy

Evaporative Cooling

Evaporation and volatility Evaporation – molecules at the surface gain enough energy to overcome attractive intermolecular forces (IMF) Volatility – measure of evaporation rate – depends on temperature and IMF

Volatility Kinetic Energy # of Particles Boltzmann Distribution tempvolatilityIMFvolatility

Boiling – Fixed temperature

Why do liquids boil? Boiling Point – T at which liquid vapor pressure = atmospheric pressure depends on P atm & IMF – Normal boiling point - b.p. at 1 atm IMFb.p.P atm b.p.

Temperature/pressure phase diagram for water

Transition to Supercritical CO 2

Interpret phase diagram for water

Draw a phase diagram for NH 3 (used as a refrigerant in RV’s and solar cooling systems)

Ammonia phase diagram

Phase Changes Need to know… Know why liquids and solids exist at all – Failure of KMT postulate Know phase names and changes – molecular views of phases and changes – distinguish S vs. L on molecular level Explain heating curve origins and parts – Why no change in T during phase change? Explain differences and similarities between evaporation, volatility and boiling Explain evaporative cooling on a molecular level Interpret temperature-pressure phase diagrams