Chapter 9Liquids and Solids

16.1 Intermolecular Forces 16.2 The Liquid State 16.3 An Introduction to Structures and Types of Solids 16.4 Structure and Bonding in Metals 16.5 Carbon and Silicon: Network Atomic Solids 16.6 Molecular Solids 16.7 Ionic Solids 16.8 Structures of Actual Ionic Solids 16.9 Lattice Defects 16.10 Vapor Pressure and Changes of State 16.11 Phase Diagrams

Intermolecular Forces: Why Condensed Phases Exist

• Intramolecular Forces– Chemical bonds

• Strong• Directional• Short Range (relative)

• Intermolecular Forces• Weaker than chemical bonds, usually much weaker• Less directional than covalent bonds• Longer range than covalent bonds

• Condensed Phases– Solids and Liquids– Intermolecular forces: attractions between molecules that are in close

proximity (i.e. in liquids and solids)

The boiling points of the covalent hydrides of elements in Groups 4A, 5A, 6A, and 7A.

Intermolecular Interactions(van der Waals forces, non-bonded

interactions)

1. Are all electrostatic in nature (Coulomb’ Law rules).

2. Are not operable for a perfect gas (except for short range repulsion).

3. Are the source of molecular adhesion and cohesion in liquids.

4. Are the source of molecular adhesion and cohesion in solids.

5. Are disrupted during boiling or evaporation.6. Are between molecules, not within molecules

1. Charge-Charge (Ion-Ion, example NaCl)2. Ion-Dipole [example NaCl (aq)]3. Dipole-Dipole (example acetone, water)

(includes H-bonding) 4. Dipole-Induced Dipole and ion-Induced dipole

[example benzene (aq)]5. London Dispersive Forces

[fluctuating dipoles, example He (l), N2(l)]6. Short Range Repulsion (helps prevent black hole

formation)

Intermolecular Interactions(van der Waals forces)

Types of Non-Bonded (Intermolecular) Attractions

Ion-Dipole Interactions

Types of Non-Bonded (Intermolecular) Attractions

Dipole-Dipole Interactions (1)

Types of Non-Bonded (Intermolecular) Attractions

Dipole-Dipole Interactions (2)Hydrogen Bonding (a non-bonding interaction, not really a bond)

a water molecule

Types of Non-Bonded (Intermolecular) Attractions

Ion-Induced Dipole

Argon Atom

Argon Atom

Types of Non-Bonded (Intermolecular) Attractions

London Dispersion• transient fluctuations of

electron distributions

Kinetic Theory of Liquids and Solids

• Intermolecular distances– Solids: 3 X 10 -10 m = 0.3 nm = 3 Å– Liquids: about 5 X 10 -10 m = 0.5 nm = 5 Å (not for water)– Gases: about 30 X 10 -10 m = 3.0 nm = 30 Å (depends on pressure)

• Intramolecular distances about 0.15 nm = 1.5 Å

The Liquid State

• Characteristics of the Liquid State– Low compressibility– High density, relative to gases– Surface tension– Exhibit capillary action

• Cohesive forces• Adhesive forces

– Viscosity

The Liquid State

• Characteristics of the Liquid State– Low compressibility– High density, relative to gases– Surface tension– Exhibit capillary action

• Cohesive forces• Adhesive forces

– ViscosityViscosity describes a liquid’s internal resistance to flow

• water has a lower viscosity

• vegetable oil has higher viscosity.

A molecule in the interior of a liquid is attracted to the molecules surrounding it, whereas a molecule at the surface of liquid is attracted only by molecules below it and on each side of it.

Cohesive forces bind molecules of the same type togetherAdhesive forces bind a substance to a surface

• Adhesive Forces and Capillary ActionX

X

X

X

X

X

X

xWater’s adhesive forces > cohesive forces,

causing a concave meniscus.

An Introduction to Structures and Types of Solids

1. Crystalline Solids– Highly regular arrangement– “Lattice”: 3D arrangement, with unit cell structures

• Simple cubic (Po metal)• Body-centered cubic (Ur metal)• Face-centered cubic (Au metal)

2. Amorphous Solids– Disordered structures– Non-crystalline– E.g., window glass

Three cubic unit cells and the corresponding lattices.

Examples of three types of crystalline solids.Atomic Solids Ionic Solids Molecular Solids

X-rays scattered from two different atoms may reinforce (constructive interference) or

cancel (destructive interference) one another.

d = distance between atoms

λ = wavelength

Reflection of X raysBragg Equation

n λ = 2 d sin θ