Chapter Nine

1

States of Matter and Intermolecular Forces

Chapter ElevenChapter Eleven

Chapter Nine

2

• ___________ ______ (bonds) govern molecular properties such as molecular geometries and dipole moments.

• ______________ _____ determine the macroscopic physical properties of liquids and solids.

• This chapter:– describes changes from one state of matter to another.– explores the types of intermolecular forces that

underlie these and other physical properties of substances.

Chapter Preview (page 433)

Chapter Nine

3

Molecular Forces Compared

Figure 11.1 (page 434)

Chapter Nine

4

States of Matter Compared

Intermolecular forces are of little significance; why?

Intermolecular forces must be

considered.

Intermolecular forces are very

important.

Figure 11.2 (page 434)

Chapter Nine

5

Phase ChangesVaporization and Condensation (page 435)

• _____________ is the conversion of a liquid to a gas, l g, this is a process. (Later we will have _____)

• The ________ __ ___________ (Hvapn) is the quantity of heat that must be absorbed to vaporize a given amount of liquid at a constant temperature. The heat associated with the process of vaporization.

• _______________ is the reverse of vaporization. So many things in chemistry occur in opposites.

• The ________ __ __________ (Hcondn) accompanies this change of a gas to a liquid, ______.

• Enthalpy is a function of state: therefore, if a liquid is vaporized and the vapor condensed at constant temperature, the total H must be zero:

Hvapn + Hcondn = 0Hcondn = – Hvapn

Note the sign change

Chapter Nine

6

page 435

Chapter Nine

7

Problem 17:How much heat, in kilojoules, is required to vaporize 3.530 kg of octane, C8H18?

Answer:

Chapter Nine

8

Vapor Pressure

• The ______ _________ of a liquid is the partial pressure exerted by the vapor when it is in dynamic equilibrium with the liquid at a constant temperature.

_________

Liquid Vapor__________

I remember hearing about this in Chapter 5

Chapter Nine

9

Liquid–Vapor Equilibrium

More vapor forms; rate of condensation of that

vapor increases …

… until __________ is attained.

Figure 11.3 (page 437)

Chapter Nine

10

Boiling Point and Critical Point

• _______ ____: the temperature at which the vapor pressure of the liquid equals the external pressure.

• _______ _______ _____: boiling point at 1 atm.

• Critical temperature (Tc): the highest temperature at which a liquid can exist.

• The critical pressure, Pc, is the vapor pressure at the critical temperature.

• The condition corresponding to a temperature of Tc and a pressure of Pc is called the critical point.

Chapter Nine

11

Phase Changes Involving Solids (page 442)

• _______ (fusion): transition of solid liquid.

• _______ ______: temperature at which melting occurs.– Same as freezing point!

• _______________, Hfusion, is the quantity of heat required to melt a set amount (one gram, one mole) of solid.

• ______________: transition of solid vapor.– Example: Ice cubes slowly “disappear” in the freezer.

• __________________, Hsubln, is the sum of the enthalpies of fusion and vaporization.

• ______ ____: all three phases—solid, liquid, vapor—are in equilibrium.

Chapter Nine

12

** This is what happens to a snowball in Hades **

The temperature of the solid _________ as it is heated …

Figure 11.8 (page 444)

Supercooled snowball

Below freezing

We are heating a solid: q =

We are at the _______ ____. The temperature of the solid remains ________ until the melting is complete.

We have a phase change, sl q =

We are heating a liquid: q =

Chapter Nine

13

** Phase Diagrams (page 445) **

A ______ _________ is a graphical representation of the conditions of ___________ __ _______ under which a substance exists as a solid, liquid, a gas, or some combination of these in equilibrium.

A—B, solid-vapor equilibrium. _____ phases exist on this line.

A—D, solid-liquid equilibrium. _____ phases exist on this line. A—C, liquid-vapor equilibrium.

_____ phases exist on this line.

Triple point. All three phases, s, l, g, are in equilibrium at this point.

Chapter Nine

14

** Phase Diagram for H2O **

Figure 11.13 (page 447)

Chapter Nine

15

** Intermolecular Forces (page 450) **

• … are forces _______ molecules.• They _________ melting points, freezing points, and

other _________ __________.• Types of intermolecular forces include:• ____________ (aka London) forces

Dispersion forces arise because the electron cloud is not perfectly uniform. Tiny, momentary dipole moments can exist even in nonpolar molecules.

• ______________ forces. In molecules with permanent dipoles

• _________________ (a special type of dipole-dipole force)

Chapter Nine

16** Dispersion Forces Illustrated **

At a given instant, electron density, even in a nonpolar molecule like this one, is ___ __________ ________.

The region of (_____________) higher electron density attains a small (–) charge …

When another nonpolar molecule __________ …

… the other end of the molecule is slightly (+).

Chapter Nine

17

… this molecule _________ a tiny dipole moment …

… in this molecule.

Opposite charges ________.

This is the ____________ _____ of attraction known as the ____________ (London) force.

Chapter Nine

18

Strength of Dispersion Forces

• Dispersion force strength depends on ______________: the ease with which the electron cloud is distorted by an external electrical field.

• The ________ the polarizability of molecules, the _________ the dispersion forces between them.

• Polarizability in turn depends on molecular size and shape.

• Heavier molecule => more electrons => a more- polarizable molecule.

Chapter Nine

19

** Dipole–Dipole Forces **

• A ______ _______ has a positively charged “end” (δ+) and a negatively charged “end” (δ–).

• When molecules come close to one another, repulsions occur between like-charged regions of dipoles. Opposite charges tend to attract one another.

• The more polar a molecule, the more pronounced is the effect of dipole–dipole forces on physical properties.

Chapter Nine

20

** Dipole–Dipole Interactions (page 452) **

__________ attract!

Chapter Nine

21

** Hydrogen Bonds (page 454) **

• A _________ ______ is an intermolecular force in which:– a _________ ____ that is covalently bonded to a (small,

electronegative) nonmetal atom in one molecule …

– is simultaneously attracted to a (small, electronegative) nonmetal atom of a neighboring molecule.

Y ––– H - - - Z ~~~~When Y and Z are small

and highly electronegative (__________) …

… this force is called a ________ ____; a special,

______ type of dipole–dipole force.

Chapter Nine

22

** Hydrogen Bonds in Water **

Figure 11.20 (page 455)

Chapter Nine

23

Hydrogen Bonding in Acetic Acid

Hydrogen bonding occurs __________

molecules.

Chapter Nine

24• A strong intermolecular force—the ________ _____ forms

when a H atom covalently bonded to an O, a N, or a F atom of one molecule is simultaneously attracted to an O, a N, or a F atom of another molecule.

• _________ ________ accounts for some of the unusual properties of water (for example, an unusually high boiling point and the fact that the density of liquid water is greater than the density of ice).

• ________ _______ also governs aspects of the behavior of biological molecules such as proteins and the nucleic acids.

• _________ _____ also accounts for the fact that …..

Chapter Nine

25**Problem 55:**Arrange the following substances in the expected order ofincreasing boiling point: H2O, NH3, CH4, CH3CH3. Give the reason for your ranking.

Answer:

CH4 and CH3CH3 are nonpolar. Only weak dispersion forces

NH3 has a higher non-boiling point than CH3CH3 despiteethane’s higher molecular mass, because of hydrogenbonding.

In H2O, hydrogen bonding is stronger still.

Chapter Nine

26

Liquids and Intermolecular Forces (page 459)

• Much behavior and many properties of liquids can be attributed to intermolecular forces.

• ________ ________ () is the amount of work required to extend a liquid surface and is usually expressed in J/m2.

• ________ _____ are intermolecular forces between unlike molecules.

• _________ ______ are intermolecular forces between like molecules.

• A _________ is the interface between a liquid and the air above it.

• _________ is a measure of a liquid’s __________ to flow.

Chapter Nine

27

Surface Tension

Molecules within the bulk of a liquid are attracted to more neighboring molecules than are _______ molecules.

Figure 11.26 (page 459)

Chapter Nine

28

Meniscus Formation

Water wets the glass (__________ ________) and its

attraction for glass forms a concave-

up surface.

What conclusion can we draw about the ________ ____

in mercury?

Chapter Nine

29

Comparing Viscosity

The flow of the oil is started at the same time. Which oil flows more readily?

Which oil has stronger intermolecular forces between its molecules?

Oil is mostly hydrocarbons; what kind of forces are these?

Figure 11.31 (page 461)

Highly viscous Less viscous

Chapter Nine

30

Types of Solids

• Amorphous solids have no significant long-range order.

• Crystalline solids have atoms/ions/molecules arranged in a regular pattern. Types of crystalline solids include: – Molecular solids, containing molecules held to

one another by dispersion/dipole–dipole/ hydrogen bonding forces.

– ________ (covalent) solids.– _____ solids.– _______ solids (metals).

Chapter Nine

31

** Network Covalent Solids **(page 462)

• Network solids have a network of covalent bonds that extend throughout the solid, holding it firmly together.

• The allotropes of carbon provide good examples.• __________ – Two or more forms of an element that differ

in their basic molecular structure. • Carbon Allotropes

– _______ has each carbon bonded to four other carbons in a tetrahedral arrangement using sp3 hybridization.

– _______ has each carbon bonded to three other carbons in the same plane using sp2 hybridization.

– __________ are roughly spherical collections of carbon atoms in the shape of a soccer ball.

– A _________ can be thought of as a plane of graphite rolled into a tube.

Chapter Nine

32_________: Allotrope of carbon Three-dimensional network of ____ hybridized carbon atoms. Extremely strong, rigid.

_________: Allotrope of carbon Three-dimensional network of ____ hybridized carbon atoms. Forces _______ layers are relatively weak.

Chapter Nine

33

Ionic Bonds as“Intermolecular” Forces (page 464)

• There are no molecules in an ionic solid, and therefore there can’t be any intermolecular forces.

• The attractions are electrostatic interionic attractions.

• _______ ____ (Chapter 9) is a measure of the strength of interionic attraction.

• The attractive force between a pair of oppositely charged ions _________:– as the ________ on the ions ________.

– as the ionic radii _________.

• Lattice energies increase accordingly.

Chapter Nine

34

Interionic (between ions) Forces of Attraction

Melting point of NaCl is about 801 oC.

Mg2+ and O2– have much stronger forces of attraction for one another than do Na+ and Cl–. Melting point of MgO is about 2800 oC.

Figure 11.36 (page 465)

Chapter Nine

35

Crystal Lattices (page 466)

• To describe crystals, three-dimensional views must be used.

• The repeating unit of the lattice is called the _____ _____.

• There are a number of different types of unit cell; hexagonal, rhombic, cubic, etc.

• The three types of _____ unit cells are: simple cubic, body-centered cubic (bcc), face-centered cubic (fcc).

Chapter Nine

36

Cubic Unit Cells Figure 11.39 (page 467)

The unit cell is a ____ in each

case.

Whole atoms shown for

clarity.

simple body-centered face-centeredcubic cubic cubic

Chapter Nine

37

Unit Cells – Coordination Number

The ____________ ______ is the number of nearest neighbor particles to a single particle in the crystal

In a ______ ____ structure, the coordination number is __ (__ nearest neighbors)

Chapter Nine

38

1. ___________ - 1 Atom at each of the corners of a cube.  These atoms are shared equally with adjacent unit cells. The coordination number is 6.                 (8 corners) (1/8 atom at corner) = 1 atom/unit cell

2. _________________ - 1 atom at each of the corners of a cube.  These atoms are shared equally with adjacent unit cells, plus 1 atom in the center.  The coordination number is 8.

(8 corners) (1/8 atom at corner) + 1 atom in center = 2 atoms/unit cell

3. _________________ - 1 atom at each of the corners of a cube.  These atoms are shared equally with adjacent unit cells plus 1 atom at each of the 6 faces of the cube.  The coordination number is 12.

(8 corners) (1/8 atom at corner) + (6 faces) (1/2 atom/face) = 4 atoms/unit cell

Chapter Nine

39

Close-Packed Structures

A _____ _______ structure in two

dimensions.

Figure 11.42 (page 468)

Chapter Nine

40

Sum and Substance

• A ________, when repeated in three dimensions, generates the entire crystal lattice.

• Unit cell properties and dimensions, often measured by X-

ray crystallography, can be used to find atomic radii and the densities of crystalline substances.

• The crystal structures of metals can be described as the packing of spheres.

• The two types of close-packing of spheres, ___________

_______ ______ (hcp) and _______________ (ccp), both reduce to the smallest possible fraction the volume occupied by holes or voids.