chapter 14 liquids and solids chapter 14 table of contents 2 14.1 water and its phase changes 14.2...

Chapter 14

Liquids and Solids

Chapter 14

Table of Contents

2

14.1 Water and Its Phase Changes

14.2 Energy Requirements for the Changes of State

14.3 Intermolecular Forces

14.4 Evaporation and Vapor Pressure

14.5 The Solid State: Types of Solids

14.6 Bonding in Solids

Chapter 14

Table of Contents

3

Intermolecular Forces

Oδ-

Hδ+ Hδ+

Oδ-

Hδ+ Hδ+

Oδ-

Hδ+ Hδ+

Dipole-Dipole Forces

Solid

Liquid Gas

+ +

-

Section 14.1

Water and Its Phase Changes

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Copyright © Cengage Learning. All rights reserved 4

Reviewing What We Know

• Gases Low density Highly compressible Fill container

• Solids High density Slightly compressible Rigid (keeps its shape)

Section 14.1


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Heating/Cooling Curve

Section 14.1


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6

Heating/Cooling Curve

• Normal boiling point: at 1 atm = 100°C • Normal freezing point: at 1 atm = 0°C • Density

Liquid water = 1.00 g/mL Ice = 0.917 g/mL

Section 14.1


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Concept Check

During the process of melting ice by adding heat, the temperature of the ice/liquid water slurry

a) stays constant.b) increases.c) decreases.d) cannot be predicted.

Energy Requirements for the Changes of State

Section 14.2

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• Changes of state are physical changes. No chemical bonds

are broken. • When a substance changes

from solid to liquid to gas, the molecules remain intact.

• The changes in state are due to changes in the forces among molecules rather than in those within the molecules.


Section 14.2

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9

• Molar heat of fusion – energy required to melt 1 mol of a substance.

• Molar heat of vaporization – energy required to change 1 mol of a liquid to its vapor.


Section 14.2

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Concept Check

Which would you predict to be larger for a given substance: Hvap or Hfus?

Explain why.


Section 14.2

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11

Concept Check

The unusually high value of the molar heat of vaporization of water (40.6 kJ/mole) is an important factor in moderating the temperature of the earth’s surface, and results in an enormous transfer of energy to the atmosphere as liquid water evaporates as part of the hydrologic cycle. Calculate the amount of heat in kJ needed to evaporate 10.5 kg of liquid water at 100.oC.

a) 4.27 × 105 kJb) 3.15 × 104 kJc) 2.37 × 104 kJd) 1.18 × 103 kJ

422

2

1 mol H O1000 g 40.6 kJ10.5 kg H O 2.37 10 kJ

1 kg 18.016 g H O mol


Section 14.2

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12

Intramolecular Forces

• “Within” the molecule.• Molecules are formed by sharing electrons

between the atoms.• Hold the atoms of a molecule together.


Section 14.2

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• Forces that occur between molecules.

• Intramolecular bonds are stronger than intermolecular forces.


Section 14.2

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Concept Check

Which are stronger, intramolecular bonds or intermolecular forces?

How do you know?


Section 14.3

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15

• Forces that occur between molecules. Dipole–dipole forces

Hydrogen bonding London dispersion forces


Section 14.3

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Dipole–Dipole Attraction


Section 14.3

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Dipole-Dipole Forces

• Dipole moment – molecules with polar bonds often behave in an electric field as if they had a center of positive charge and a center of negative charge.

• Molecules with dipole moments can attract each other electrostatically. They line up so that the positive and negative ends are close to each other.

• Only about 1% as strong as covalent or ionic bonds.


Section 14.3

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18

Hydrogen Bonding

• Strong dipole-dipole forces.• Hydrogen is bound to a highly electronegative

atom – nitrogen, oxygen, or fluorine.


Section 14.3

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19

Hydrogen Bonding in Water

• Blue dotted lines are the intermolecular forces between the water molecules.

Hydrogen Bonds hold DNA together.


Section 14.3

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Hydrogen Bonding

• Affects physical properties Boiling point Melting point


Section 14.3

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About 70% of our planet is covered by water. Perhaps we should call it not “earth” but “ocean”. Where did the water come from?


Section 14.3

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Some say the water came from comets (mostly water) colliding with earth…Why did thy not collide with other planets that have no water??? Jupiter is 317 times the mass of the earth! Shoemaker-Levi colliding with Jupiter.


Section 14.3

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Moon rocks have been found to be as old as 4.527 billion years while the oldest earth rock has been found to be 4.28 billion years old. Moon rocks have been found to be magnetic (when they cooled they were under a magnetic field caused by a rapidly rotating planet). The moon is not rotating rapidly now.

The moon and the earth have not always been together!!!

Johnson Space Center Moon Rock Bldg.


Section 14.3

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London Dispersion Forces

• Instantaneous dipole that occurs accidentally when a given atom induces a similar dipole in a neighboring atom.

• Significant in large atoms/molecules.• Occurs in all molecules, including nonpolar

ones.


Section 14.3

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London Dispersion Forces – Nonpolar Molecules


Section 14.3

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London Dispersion Forces

• Become stronger as the sizes of atoms or molecules increase.


Section 14.3

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27

Melting and Boiling Points

• In general, the stronger the intermolecular forces, the higher the melting and boiling points.


Section 14.3

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Concept Check

Which molecule is capable of forming stronger intermolecular forces?

N2 H2O

Explain.


Section 14.3

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Concept Check

Draw two Lewis structures for the formula C2H6O and compare the boiling points of the two molecules.

C

H

H C

H

H

H

O H C

H

H C

H

H

H

O H


Section 14.3

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Concept Check

Which gas would behave more ideally at the same conditions of P and T?

CO or N2

Why?


Section 14.3

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Concept Check

Consider the following compounds:

NH3 CH4 H2

How many of the compounds above exhibit London dispersion forces?

a) 0

b) 1

c) 2

d) 3

Section 14.4

Evaporation and Vapor Pressure

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32

Vaporization or Evaporation

• Molecules of a liquid can escape the liquid’s surface and form a gas.

• Endothermic process – requires energy to overcome the relatively strong intermolecular forces in the liquid.

Section 14.4


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Vapor Pressure

• Amount of liquid first decreases then becomes constant. • Condensation - process by which vapor molecules

convert to a liquid. • When no further change is visible the opposing

processes balance each other – equilibrium

Section 14.4


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34

Vapor Pressure

• Pressure of the vapor present at equilibrium.• The system is at equilibrium when no net

change occurs in the amount of liquid or vapor because the two opposite processes exactly balance each other.

Section 14.4


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35

Ilustration of Vapor Pressure

Budda

Water

Budda (air pressure) will keep the liquid water down while the heat vaporizes the surface water.

Who’s this?

Section 14.4


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36

Ilustration of Vapor Pressure

WaterWhen the vapor pressure exceeds the air pressure, Budda cannot keep the liquid water down.

Then Budda rises and vapor bubbles form throughout the liquid. And it boils!

Section 14.4


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Concept Check

What is the vapor pressure of water at 100°C? How do you know?

1 atm

Section 14.4


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Vapor Pressure

• Liquids in which the intermolecular forces are strong have relatively low vapor pressures.

Section 14.4


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Concept Check

Which of the following would be expected to have the highest vapor pressure at room temperature?

a) CH3CH2CH2OHb) CH3CH2CH2NH2

c) CH3CH2CH2CH3

d) CH3CH2CH3

Section 14.5

The Solid State: Types of Solids

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Crystalline Solids

• Regular arrangement of their components.

Section 14.5


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41

Types of Crystalline Solids

Diamonds

Section 14.5


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42

Types of Crystalline Solids

• Ionic Solids – ions at the points of the lattice that describes the structure of the solid.

• Molecular Solids – discrete covalently bonded molecules at each of its lattice points.

• Atomic Solids – atoms at the lattice points that describe the structure of the solid.

Section 14.5


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Examples of Three Types of Crystalline Solids

Section 14.6

Bonding in Solids

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Examples of the Various Types of Solids

Section 14.6

Bonding in Solids

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Ionic Solids

• Stable substances with high melting points. • Held together by strong forces between ions.

Section 14.6

Bonding in Solids

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Molecular Solids

• Fundamental particle is a molecule. • Melt at relatively low temperatures. • Held together by weak intermolecular forces.

Section 14.6

Bonding in Solids

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47

Atomic Solids

• Fundamental particle is the atom. • Properties vary greatly.

Group 8 – low melting points Diamond – very high melting point

Section 14.6

Bonding in Solids

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48

Dr. Tacy Hall’s Artificial Diamond Presses

Pictures to the left and below are of diamonds made from graphite. Dr. Hall made diamonds from

peanut butter as well.

Section 14.6

Bonding in Solids

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49

Bonding in Metals

• Metals are held together by nondirectional covalent bonds (called the electron sea model) among the closely packed atoms.

The word ICE made from Nitinol wire, stretched, reforms in warm water.

Section 14.6

Bonding in Solids

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Bonding in Metals

• Metals form alloys of two types. Substitutional – different atoms are substituted for

the host metal atoms.

Section 14.6

Bonding in Solids

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Bonding in Metals

• Metals form alloys of two types. Interstitial – small atoms are introduced into the

“holes” in the metallic structure.

chapter 14 liquids and solids chapter 14 table of contents 2 14.1 water and its phase changes 14.2...

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