Intermolecular Forces, Liquids, and Solids www.njctl.org Slide 3 / - - PDF document

This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others.

Click to go to website: www.njctl.org New Jersey Center for Teaching and Learning Progressive Science Initiative

Slide 1 / 90

www.njctl.org

Intermolecular Forces, Liquids, and Solids

Slide 2 / 90 Table of Contents

· States of Matter

Click on the topic to go to that section

· Properties of Gases · Measuring Pressure · Ideal Gas Law · Gas Density · Partial Pressure · Graham's Law of Effusion · Real versus Ideal Gases · Gas Laws

Slide 3 / 90

Return to Table of Contents

States of Matter

Slide 4 / 90

We first explained atoms, and how to build up the periodic table from quantum numbers. Then we explained how atoms combine to form molecules: the most common way we find most atoms in nature, and learned about how atoms from molecules rearrange in chemical reactions to form new chemical compounds. Now, we're going to use intermolecular forces to combine molecules to create the common states of matter.

So far this year…. Slide 5 / 90

Intermolecular forces are the piece we need to add to the puzzle to explain the world around us. Without intermolecular forces, we wouldn't have tables, lakes, wall...or even our bodies. Intermolecular forces shape our world.

Intermolecular Forces Slide 6 / 90

While there are many states of matter, the three common states that dominate our world are gases, liquids and solids. These are the states of matter we'll be studying. We won't be discussing more exotic states such as plasma, nuclear matter, etc.

States of Matter Slide 7 / 90 States of Matter

The 2 fundamental differences between states of matter are: the distance between particles the particles' freedom to move

Slide 8 / 90 States of Matter

cool or increase pressure heat or decrease pressure

cool heat

Particles are far apart, total freedom, much of empty space, total disorder disorder, freedom, free to move relative to each other, close together

• rdered arrangement,

particles are in fixed positions, close together

Gas Liquid Crystalline solid

Slide 9 / 90

Solid Liquid Gas

Enjoy this musical interlude by They Might Be Giants!

Slide 10 / 90

Characteristics of the States of Matter

VOLUME SHAPE FLOW DIFFUSION

Gas

Assumes the shape of its container Expands to the volume of its container

COMPRESSION

Is compressible Flows easily Very Rapid

Slide 11 / 90

Characteristics of the States of Matter

VOLUME SHAPE FLOW DIFFUSION

Liquid

Assumes the shape of the part of a container it occupies Does not expand to the volume

• f the container

COMPRESSION

Is virtually incompressible Flows easily Within a liquid, slow

Slide 12 / 90

Characteristics of the States of Matter

VOLUME SHAPE FLOW DIFFUSION

Solid

Retains its own shape regardless of container Does not expand to the volume of its container

COMPRESSION

Is virtually incompressible Does not flow Within a solid, very very slow

Slide 13 / 90

In the solid and liquid states particles are closer together, we refer to them as condensed phases.

Condensed Phases

cool or increase pressure heat or decrease pressure

cool heat

Particles are far apart, total freedom, much of empty space, total disorder disorder, freedom, free to move relative to each other, close together

• rdered arrangement,

particles are in fixed positions, close together

Gas Liquid Crystalline solid

Slide 14 / 90

1 Which of the below is a characteristic of a gas?

A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is not compressible. E Diffusion is very slow within it.

Answer

Slide 15 / 90

1 Which of the below is a characteristic of a gas?

A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is not compressible. E Diffusion is very slow within it.

[This object is a pull tab]

Answer C

Slide 15 (Answer) / 90

2 Which of the below is a characteristic of a liquid?

A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is compressible. E Diffusion is very rapid within it.

Answer

Slide 16 / 90

2 Which of the below is a characteristic of a liquid?

A It fills only a portion of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is compressible. E Diffusion is very rapid within it.

[This object is a pull tab]

Answer A

Slide 16 (Answer) / 90

3 Which of the below is a characteristic of a solid?

A It fills all of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is compressible. E Diffusion is very rapid within it.

Answer

Slide 17 / 90

3 Which of the below is a characteristic of a solid?

A It fills all of its container. B Its molecules are in relatively rigid positions. C It takes on the shape of its entire container. D It is compressible. E Diffusion is very rapid within it.

[This object is a pull tab]

Answer B

Slide 17 (Answer) / 90

The state of a substance at a particular temperature and pressure depends on two opposing properties: Intermolecular Forces, which pulls them together Kinetic energy of the particles, which pulls them apart Without intermolecular forces (IMF's), all molecules would be ideal gases...there would be no liquids or solids.

States of Matter Slide 18 / 90

Boiling represents a transition from a liquid to a gas. To make that transition, molecules in the liquid must break free

• f the intermolecular forces that bind them.

Intermolecular Forces & Boiling Points Slide 19 / 90

The kinetic energy of the molecules is proportional to the temperature: as temperature rises, so does kinetic energy. The boiling point refers to the temperature at which the molecules' energy overcomes the intermolecular forces binding them together. The higher the boiling point of a substance, the stronger the intermolecular forces.

Intermolecular Forces & Boiling Points

Water molecules

• vercome their

intermolecular forces at 100 C.

Slide 20 / 90 Intermolecular Forces

The attractions between molecules, intermolecular forces, are not nearly as strong as the intramolecular attractions that hold compounds together. They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities.

H Cl H Cl Intermolecular attraction ( weak) Covalent bond (strong)

Slide 21 / 90

There are three types of Intermolecular Forces: they are sometimes called van der Waals Forces Dipole-dipole interactions Hydrogen bonding London dispersion forces (LDF's)

Intermolecular Forces Slide 22 / 90 Dipole-Dipole Interactions

A dipole is a polar molecule. Molecules that have permanent dipoles are attracted to each

• ther.

The positive end of one is attracted to the negative end of the other and vice-versa. These forces are only important when the molecules are close to each other.

+

• +
• +
• +
• +
• +
• The interaction between any

two opposite charges is attractive ( red) The interaction between any two like charges is repulsive (black)

Only polar molecules will have this type

• f Intermolecular Force.

Slide 23 / 90

The polarity of a molecule is measured by its dipole moment, m. The more polar the molecule, the greater its dipole moment. The more polar the molecule, the higher its boiling point. That's because the attraction between the dipoles holds the molecules together, not letting them boil away.

Dipole-Dipole Interactions

Substance Acetonitrile, CH3CN 41 3.9 355 Acetaldehyde, CH3CHO 44 2.7 294 Methyl chloride, CH3Cl 50 1.9 249 Dimethyl ether, CH3OCH3 46 1.3 248 Propane, CH3CH2CH3 44 0.1 231 Molecular Weight (amu) Dipole Moment u(D) Boiling Point (k)

Slide 24 / 90

4 Which of the below molecules will have the highest boiling point?

A CH3CH2CH3 B CH3OCH3

Substance

Molecular Wt. Dipole Moment

CH3CH2CH3 44

0.1

CH3OCH3

46 1.3 CH3Cl 50 1.9

CH3CHO

44 2.7

CH3CN

41 3.9

C CH3Cl D CH3CHO E CH3CN

Answer

Slide 25 / 90

5 Which of the below molecules will have the lowest boiling point?

Substance

Molecular Wt. Dipole Moment CH3CH2CH3

44 0.1

CH3OCH3

46 1.3 CH3Cl 50 1.9

CH3CHO

44 2.7

CH3CN

41 3.9

A CH3CH2CH3 B CH3OCH3

C CH3Cl D CH3CHO E CH3CN

Answer

Slide 26 / 90 London Dispersion Forces

London Dispersion Forces occur between all molecules. They result from the fact that electrons are in constant motion and sometimes are the same side of the molecule. When they are on one side, the molecule is polarized: one side is negative and the other is positive; the molecule acts like a dipole.

• δ

+

δ-

Slide 27 / 90

• δ

+

δ

• δ+

δ-

London Dispersion Forces

That polarization creates an electric field that oppositely polarizes nearby molecules...leading to an attraction.

Slide 28 / 90 London Dispersion Forces

While the electrons in helium repel each other, they

• ccasionally wind up on the same side of the atom.

At that instant, the helium atom is polar, with an excess of electrons on one side and a shortage on the other.

2+ e- e-

Helium atom

δ

+

δ-

Slide 29 / 90 London Dispersion Forces

Another helium atom nearby, has a dipole induced in it, as the electrons

• n the left side of the first atom repel the electrons in the second.

London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.

2+ e- e- 2+ e- e-

Helium atom 1 Helium atom 2 electrostatic attraction

δ- δ

+

δ

+

δ

• Slide 30 / 90

These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability. Because larger molecules have more electrons, they are more polarizable. Molecules with more electrons experience stronger London Dispersion Forces.

Polarizability Slide 31 / 90

6 Molecules with more electrons experience stronger London Dispersion Forces. True False

Answer

Slide 32 / 90

6 Molecules with more electrons experience stronger London Dispersion Forces. True False

[This object is a pull tab]

Answer True

Slide 32 (Answer) / 90

Examine the trends among the halogens and the noble gases:

London Dispersion Forces

Halogen Number

• f

electrons Boiling Point (K) Noble gas Number

• f

electrons Boiling point (K)

F2 18

85.1 He

2

4.6 Cl2 34

238.6 Ne

10 27.3 Br2 70

332.0 Ar

18 87.5 I2 106

457.6 Kr

36

120.9

Xe 54

166.1

the greater the number of electrons, the more polarizable the particles are, resulting in stronger London dispersion forces.

Slide 33 / 90

7 Which of the following molecules will have the highest boiling point? A F2 B Cl2 C Br2 D I2

Answer

Slide 34 / 90

7 Which of the following molecules will have the highest boiling point? A F2 B Cl2 C Br2 D I2

[This object is a pull tab]

Answer D

Slide 34 (Answer) / 90

8 Which of the below molecules will have the lowest boiling point?

A

F2

B

Cl2

C

Br2

D

I2

Answer

Slide 35 / 90

8 Which of the below molecules will have the lowest boiling point?

A

F2

B

Cl2

C

Br2

D

I2

[This object is a pull tab]

Answer A

Slide 35 (Answer) / 90

9 Which of the below molecules will have the highest boiling point?

A

He

B

Ne

C

Ar

D

Kr

E

Xe

Answer

Slide 36 / 90

9 Which of the below molecules will have the highest boiling point?

A

He

B

Ne

C

Ar

D

Kr

E

Xe

[This object is a pull tab]

Answer E

Slide 36 (Answer) / 90

10 Which of the below molecules will have the lowest boiling point?

A He B Ne C Ar D Kr E Xe

Answer

Slide 37 / 90

10 Which of the below molecules will have the lowest boiling point?

A He B Ne C Ar D Kr E Xe

[This object is a pull tab]

Answer A

Slide 37 (Answer) / 90

Which Have a Greater Effect?

Dipole-Dipole Interactions or Dispersion Forces If one molecule is much larger than another, dispersion forces will likely determine its physical properties. If molecules are nonpolar, dispersion forces will dominate, since all molecules experience dispersion forces.

Dipole-Dipole Dispersion Forces

If two polar molecules are of comparable size, dipole-dipole interactions are the dominating force.

Slide 38 / 90 Hydrogen Bonding

The graph shows the boiling points for four polar and four non-polar compounds. For the non-polar series, (CH4 to SnH4 ), boiling points increase with higher number

• f electrons. There are

stronger dispersion forces due to greater polarizability.

Slide 39 / 90 Hydrogen Bonding

Examine the boiling points for the four polar compounds (4,2,2 = bent) called Group 16 hydrides. For this series from H2 S through H2 Te, boiling points increase with increasing polarity as expected. Recall that greater differences in electronegativities make a bond more polar. What is going on with water? It would be expected to have the lowest BP in the group, but instead has the highest boliing point.

Slide 40 / 90

The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds.

Hydrogen Bonding Slide 41 / 90

Hydrogen bonding arises in part from the high electronegativity and small radius of nitrogen, oxygen, and fluorine. When hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.

Hydrogen Bonding F F

Click here to watch an animation about Hydrogen Bonding

Slide 42 / 90

Ice is the only solid that floats in its liquid form. If it didn't, life on Earth would be very different. For instance, lakes would freeze from the bottom and fish couldn't survive winters. Hydrogen bonding creates the space in ice that explains its low density.

Hydrogen Bonding

Click here to watch an animation

• f the Water - Ice transition

Slide 43 / 90

A HF B HCl C HBr D HI E

All of the above.

11 Which of the following molecules has hydrogen bonding as one of its intermolecular forces?

Answer

Slide 44 / 90

A HF B HCl C HBr D HI E

All of the above.

11 Which of the following molecules has hydrogen bonding as one of its intermolecular forces?

[This object is a pull tab]

Answer A

Slide 44 (Answer) / 90

A CH3F B CH3Cl C HBr D NO2 E

None of the above.

12 Which of the following molecules has hydrogen bonding as one of its IM forces? Answer

Slide 45 / 90

A CH3F B CH3Cl C HBr D NO2 E

None of the above.

12 Which of the following molecules has hydrogen bonding as one of its IM forces?

[This object is a pull tab]

Answer A

Slide 45 (Answer) / 90 Ion-Dipole Interactions

There is a fourth molecular force that will be important as we explore solutions later this year: Ion-dipole interactions are not considered a van der Waals force. The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents.

+

• +
• +
• +
• _

Anion- dipole attractions

+

• +
• +
• +
• +

Cation -dipole attractions

Slide 46 / 90

Interacting molecules or ions Are polar molecules involved? Are ions involved? Are polar molecules and ions both present? Are hydrogen atoms bonded to N,O,or F atoms? Ionic bonding NaCl, KI Ion- dipole forces NaCl in H2O Hydrogen bonding H2O, NH3 Dipole-dipole forces H2S, CH3Cl Dispersion forces only (induced dipoles) Ar, I2 YES YES NO NO YES YES NO NO van der Waals forces

Summary of Interactions

Click here to watch a summary of IMF

Slide 47 / 90

London dispersion forces

Dipole- dipole

Hydrogen- bonding Comparison of strength weakest IMF medium strength IMF strongest IMF

Who has it?

ALL molecules have this IMF. Nonpolar molecules have ONLY this IMF. Only POLAR molecules Only POLAR molecules with a H atom covalently bonded to N, O, or F How do you tell who has it? Molecules are nonpolar if: · · · · · · · it is diatomic, or · · · · · · · last VSEPR number is zero

Molecules are polar if: · · · · · · · it's made of ONLY 2 different atoms, or · · · · · · · Last VSEPR number is non-zero (except 642, 523 are NONpolar)

See above

What if there is a tie within a category? Look at # of electrons Look at the dipole moment (given) Look at which molecule has more N-H, O-H, or F-H bonds

Summary of IMF

Slide 48 / 90

13 Which of the following molecules has London dispersion as its only IM force?

A

PH3

B

H2S

C

HCl

D

SiH4

E

None of the above.

Answer

Slide 49 / 90

13 Which of the following molecules has London dispersion as its only IM force?

A

PH3

B

H2S

C

HCl

D

SiH4

E

None of the above.

[This object is a pull tab]

Answer D

Slide 49 (Answer) / 90

14 How many of these substances will have dipole- dipole interactions? (How many are polar molecules?)

A 0 B 1 C 2 D 3 E 4

H2O CO2 CH4 NH3

Answer

Slide 50 / 90

14 How many of these substances will have dipole- dipole interactions? (How many are polar molecules?)

A 0 B 1 C 2 D 3 E 4

H2O CO2 CH4 NH3

[This object is a pull tab]

Answer C

Slide 50 (Answer) / 90

15 Which of the following molecules will have the highest boiling point?

A

H2O

B

CO2

C

CH4

D

NH3

Answer

Slide 51 / 90

15 Which of the following molecules will have the highest boiling point?

A

H2O

B

CO2

C

CH4

D

NH3

[This object is a pull tab]

Answer A

Slide 51 (Answer) / 90

16 Of the following diatomic molecules, which has the highest boiling point?

A N2 B

Br2

C H2 D

Cl2

E

O2

Answer

Slide 52 / 90

16 Of the following diatomic molecules, which has the highest boiling point?

A N2 B

Br2

C H2 D

Cl2

E

O2

[This object is a pull tab]

Answer B

Slide 52 (Answer) / 90

17 Of the following diatomic molecules, which has the lowest boiling point?

A N2 B Br2 C H2 D Cl2 E O2

Answer

Slide 53 / 90

17 Of the following diatomic molecules, which has the lowest boiling point?

A N2 B Br2 C H2 D Cl2 E O2

[This object is a pull tab]

Answer C

Slide 53 (Answer) / 90

18 Which one of the following derivatives of methane (CH4) has the lowest boiling point?

A

CBr4

B

CF4

C

CCl4

D

CI4

Answer

Slide 54 / 90

18 Which one of the following derivatives of methane (CH4) has the lowest boiling point?

A

CBr4

B

CF4

C

CCl4

D

CI4

[This object is a pull tab]

Answer B

Slide 54 (Answer) / 90

19 Which one of the following derivatives of methane (CH4) has the highest boiling point?

A CBr4 B CF4 C CCl4 D CI4

Answer

Slide 55 / 90

19 Which one of the following derivatives of methane (CH4) has the highest boiling point?

A CBr4 B CF4 C CCl4 D CI4

[This object is a pull tab]

Answer D

Slide 55 (Answer) / 90

Intermolecular Forces Affect Many Physical Properties

The strength of the attractions between particles can greatly affect the properties of a substance or solution.

Slide 56 / 90 Viscosity

Resistance of a liquid to flow is called viscosity. It is related to the ease with which molecules can move past each

• ther. Viscosity increases with stronger intermolecular forces and

decreases with higher temperature.

Substance Formula Viscosity ( kg/m-s) Hexane CH3CH2CH2CH2CH2CH3 3.26 x 10-4 Heptane CH3CH2CH2CH2CH2CH2CH3 4.09 x 10-4 Octane CH3CH2CH2CH2CH2CH2CH2CH3 5.42 x 10-4 Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3 7.11 x 10-4 Decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 1.42 x 10-3

Slide 57 / 90 Surface Tension

Surface tension results from the net inward force experienced by the molecules on the surface of a liquid.

Slide 58 / 90

Phase Changes

Vaporization Condensation Sublimation Melting Freezing Deposition GAS SOLID Energy of system

LIQUID

Slide 59 / 90 Energy Changes Associated with Changes of State

Chemical and physical changes are usually accompanied by changes in energy. When energy is put into the system, the process is called endothermic. When energy is released by the system, the process is called exothermic.

Slide 60 / 90

20 Which of the following is not a phase change?

A vaporization B effusion C melting D sublimation

Slide 61 / 90

Boiling vs. Evaporation

Boiling and evaporation are two ways in which a liquid can vaporize into a gas. However, there are important distinctions between these processes. Boiling Evaporation

• ccurs at a specific

temperature, the boiling point (B.P.)

• ccurs below the boiling

point

• ccurs throughout the

entire liquid

• ccurs only at the surface of

a liquid achieved when atmospheric pressure equals vapor pressure (Patm = Pvap)

Slide 62 / 90 Vapor Pressure

Vapor pressure is defined as the pressure exerted by gas molecules above the surface of an enclosed liquid. Sample (A) at a lower temperature shows some vapor above the surface of the liquid. Sample (B) at a higher temperature shows a greater number of vapor particles, thus resulting in higher vapor pressure. (B) (A)

Slide 63 / 90 Vapor Pressure

At any temperature some molecules in a liquid have enough energy to escape. As the temperature rises, the fraction of molecules that have enough energy to escape increases.

Slide 64 / 90

Liquid - Vapor Equilibrium

As more molecules escape the liquid, the pressure they exert increases. Eventually, the liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate.

gas becomes liquid liquid becomes gas

Slide 65 / 90

Like any line, the curve is made up

• f an infinite number of points.

Each point along the curve shows the temperature at which atmospheric pressure equals vapor pressure Patm = Pvap In other words, each point along the curve indicates a boiling point.

Vapor Pressure Curve

The type of graph shown here is called a vapor pressure curve.

Slide 66 / 90

The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. The normal boiling point is the temperature at which its vapor pressure is 760 torr. (AKA 760 mm Hg = 1 atm)

Vapor Pressure Curve Slide 67 / 90

21 What is the normal boiling point of ethanol?

A 34.6 B 40.0 C 60.0 D 78.3 E 100.0

Slide 68 / 90

22 What is the boiling point ( in oC) of diethyl ether at 200 torr? A

• 10

B 0 C

760

D 35

Slide 69 / 90

23 What is the boiling point of water at 300 torr? A

200

B 50 C

100

D 75 E 90

Slide 70 / 90

Pressure Cooking

A liquid will boil when its vapor pressure equals atmospheric pressure. A pressure cooker works by increasing the "atmospheric" pressure inside it, so water will not boil at 100oC; instead, it may be heated up to 120oC before turning to steam. Raising the cooking temperature cuts cooking time drastically.

Slide 71 / 90 Pressure Cooking

www.washingtonpost.com

Slide 72 / 90 Boiling and Pressure

Since atmospheric pressure is so low at high altitudes, (e.g. top of Mount Everest) water will boil at a much lower temperature than in New Jersey.

Patm = 33 kPa on Mt. Everest Patm = 101.3 kPa at sea level

Click here for a video of water boiling at room temperature Recall that boiling occurs when Pvap = Patm

Slide 73 / 90

24 It will take longer to hard-boil an egg (cooking time only)

A on top of Mt. Everest B at sea level C cooking times are equal

Slide 74 / 90 Volatility

The more volatile a liquid: The more quickly it evaporates The higher its vapor pressure at a given temperature The weaker its Intermolecular Forces Volatility is another characteristic of a liquid that is based upon the strength of its intermolecular forces.

Slide 75 / 90 Phase Diagrams

Phase diagrams display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases.

Slide 76 / 90

The circled line is the liquid-vapor interface. It starts at the triple point (T), the point at which all three states are in equilibrium.

Phase Diagrams Slide 77 / 90 Phase Diagrams

The liquid-vapor interface ends at the critical point (C); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other.

Slide 78 / 90 Phase Diagrams

The circled line in the diagram below is the interface between liquid and solid. The melting point at each pressure can be found along this line.

Slide 79 / 90

Phase Diagrams

Below the triple point the substance cannot exist in the liquid state. Along the circled line the solid and gas phases are in equilibrium; the sublimation point at each pressure is along this line.

Slide 80 / 90 Phase Diagram of Water

Note the high critical temperature and critical pressure. These are due to the strong van der Waals forces between water molecules.

Slide 81 / 90 Comparison of Two Phase Diagrams

For carbon dioxide, the slope of the solid-liquid line is positive, as it is for most

• ther substances. This

means that an increase in pressure can cause substances to freeze. For water, the slope of the solid-liquid line is negative. This means that an increase in pressure can cause this substance to

• melt. Water is the only

substance that does this.

Slide 82 / 90

Phase Diagram of Carbon Dioxide

Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; CO2 sublimes at normal pressures. The low critical temperature and critical pressure for CO2 make supercritical CO2 a good solvent for extracting nonpolar substances (like caffeine).

Slide 83 / 90

Solids

Crystalline, in which particles are in highly ordered arrangement. We can think of solids as falling into two groups. Amorphous, in which there is no particular order in the arrangement of particles.

NDT Education Resource Center

Slide 84 / 90 Amorphous Solids

Crystalline solids include ionic compounds, metals and another group called covalent-network solids. Crystalline solids are categorized by bonding type as shown on the next slide. Some examples of amorphous solids are: rubber, glass, paraffin wax and cotton candy.

Slide 85 / 90

Types of Bonding in Crystalline Solids Slide 86 / 90 Covalent-Network Solids: Diamond

Diamonds are an example

• f a covalent-network solid,

in which carbon atoms are covalently bonded to four

• ther carbon atoms.

They tend to be hard and have high melting points.

Slide 87 / 90

Graphite is another example

• f a covalent-network solid.

Each carbon atom is covalently bonded to 3 others in layers of interconnected hexagonal rings. The layers are held together by weak dispersion forces. The layers slide easily across

• ne another, so graphite is

used as a lubricant as well as the "lead" in pencils.

Covalent-Network Solids: Graphite Slide 88 / 90

Metallic Solids

Metals are not covalently bonded, but the attractions between atoms are too strong to be van der Waals forces. In metals, valence electrons are delocalized throughout the solid. This means that the "sea" of electrons moves freely around all the nuclei.

Me Me Me Me Me Me Me Me Me Me Me Me e- e- e- e- e- e- e- e- click here for an animation about metallic bonding

Slide 89 / 90 Properties of Metallic Solids

The delocalized nature of the electrons in metals accounts for many physical properties. For example, metals are generally: good conductors of heat and electricity malleable ductile, (i.e. may be drawn into wires)

Slide 90 / 90