Untitled Flashcards Set

explain this lesson to me The Properties of Materials

Fog rolls over the Golden Gate Bridge in San Francisco, California.

OVERVIEW

In this lesson, you will investigate the properties of materials and explain how those properties relate to interactions at the molecular level.

KEY WORDS

intermolecular force

polarity

hydrogen bonding

materials science

polymer

hydrocarbon

composite

CAN YOU SOLVE IT?

Along the California coast, it is common to see fog for several days each year. In places where water resources can be scarce but fog is plentiful, some people are hoping to “harvest” water from the fog. Scientists and engineers around the world have tested different methods for collecting water from fog. When developing water-collecting technology, the properties of the materials are especially important. Some researchers have looked to nature for inspiration, studying plants and animals that collect water from the air. For example, some desert insects are able to capture water on their bodies. Understanding how living things attract water to their bodies allows scientists to develop materials that can do the same. Materials scientists look for patterns in how natural fog-collecting systems work and then investigate how these patterns can be applied to human-made systems. Observing Properties of Compounds

A student's hair rises up to a balloon held above her head.

Static makes a person’s hair stick to a balloon.

Have you ever rubbed a balloon on your head? If so, you may have noticed that "static" makes your hair stand up. You also may have noticed that your hair sticks to the balloon, a phenomenon commonly known as "static cling."

Forces Between Particles

Opposite charges are positive and negative. Opposite charges attract each other. Like charges are both negative or both positive. Like charges repel each other.

Charged particles may attract or repel each other.

Most materials have no overall charge because they have equal numbers of protons and electrons. When you rub a balloon on your hair, however, electrons from atoms in your hair are transferred to atoms in the balloon. This transfer makes some atoms in your hair positively charged and some atoms in the balloon negatively charged. Because like charges repel, the positively charged strands of your hair spread far away from one another. Opposite charges attract, so the positively charged hair sticks to the negatively charged balloon. Repulsions and attractions due to electric charge are known as electric force. Another name for electric force is the Coulomb force.

MATH CONNECTION

Calculating Force

Coulomb’s law describes how to calculate electric force. This law states that the magnitude of the electric force (Felectric) between two point charges (q1 and q2) is directly related to the product of the charges and inversely related to the square of the distance (d) between them. The Coulomb constant (kC) is a constant used in the calculation of electric force. The equation for Coulomb’s law is:

COLLABORATE

As charge increases, electric force increases. However, if the distance between two charges doubles, electric force decreases by a factor of four. How does the equation for this law demonstrate these relationships between charge, distance, and force?

Glass tubes are placed open-end first into a tub of water. The water rises up the tubes, above the surface of the water in the tub.

Capillary action

Attractive forces exist between protons and electrons in atoms. In ionic compounds, strong attractive forces hold ions tightly together, which explains why these compounds have high melting points. Molecular compounds tend to have relatively low melting points, but attractive forces can still exist between molecules.

Observing Properties of Compounds

A student's hair rises up to a balloon held above her head.

Static makes a person’s hair stick to a balloon.

Have you ever rubbed a balloon on your head? If so, you may have noticed that "static" makes your hair stand up. You also may have noticed that your hair sticks to the balloon, a phenomenon commonly known as "static cling."

Forces Between Particles

Opposite charges are positive and negative. Opposite charges attract each other. Like charges are both negative or both positive. Like charges repel each other.

Charged particles may attract or repel each other.

Most materials have no overall charge because they have equal numbers of protons and electrons. When you rub a balloon on your hair, however, electrons from atoms in your hair are transferred to atoms in the balloon. This transfer makes some atoms in your hair positively charged and some atoms in the balloon negatively charged. Because like charges repel, the positively charged strands of your hair spread far away from one another. Opposite charges attract, so the positively charged hair sticks to the negatively charged balloon. Repulsions and attractions due to electric charge are known as electric force. Another name for electric force is the Coulomb force.

MATH CONNECTION

Calculating Force

Coulomb’s law describes how to calculate electric force. This law states that the magnitude of the electric force (Felectric) between two point charges (q1 and q2) is directly related to the product of the charges and inversely related to the square of the distance (d) between them. The Coulomb constant (kC) is a constant used in the calculation of electric force. The equation for Coulomb’s law is:

COLLABORATE

As charge increases, electric force increases. However, if the distance between two charges doubles, electric force decreases by a factor of four. How does the equation for this law demonstrate these relationships between charge, distance, and force?

Glass tubes are placed open-end first into a tub of water. The water rises up the tubes, above the surface of the water in the tub.

Capillary action

Attractive forces exist between protons and electrons in atoms. In ionic compounds, strong attractive forces hold ions tightly together, which explains why these compounds have high melting points. Molecular compounds tend to have relatively low melting points, but attractive forces can still exist between molecules.

Observing Properties of Compounds

A student's hair rises up to a balloon held above her head.

Static makes a person’s hair stick to a balloon.

Have you ever rubbed a balloon on your head? If so, you may have noticed that "static" makes your hair stand up. You also may have noticed that your hair sticks to the balloon, a phenomenon commonly known as "static cling."

Forces Between Particles

Opposite charges are positive and negative. Opposite charges attract each other. Like charges are both negative or both positive. Like charges repel each other.

Charged particles may attract or repel each other.

Most materials have no overall charge because they have equal numbers of protons and electrons. When you rub a balloon on your hair, however, electrons from atoms in your hair are transferred to atoms in the balloon. This transfer makes some atoms in your hair positively charged and some atoms in the balloon negatively charged. Because like charges repel, the positively charged strands of your hair spread far away from one another. Opposite charges attract, so the positively charged hair sticks to the negatively charged balloon. Repulsions and attractions due to electric charge are known as electric force. Another name for electric force is the Coulomb force.

MATH CONNECTION

Calculating Force

Coulomb’s law describes how to calculate electric force. This law states that the magnitude of the electric force (Felectric) between two point charges (q1 and q2) is directly related to the product of the charges and inversely related to the square of the distance (d) between them. The Coulomb constant (kC) is a constant used in the calculation of electric force. The equation for Coulomb’s law is:

COLLABORATE

As charge increases, electric force increases. However, if the distance between two charges doubles, electric force decreases by a factor of four. How does the equation for this law demonstrate these relationships between charge, distance, and force?

Glass tubes are placed open-end first into a tub of water. The water rises up the tubes, above the surface of the water in the tub.

Capillary action

Attractive forces exist between protons and electrons in atoms. In ionic compounds, strong attractive forces hold ions tightly together, which explains why these compounds have high melting points. Molecular compounds tend to have relatively low melting points, but attractive forces can still exist between molecules.

Observing Properties of Compounds

A student's hair rises up to a balloon held above her head.

Static makes a person’s hair stick to a balloon.

Have you ever rubbed a balloon on your head? If so, you may have noticed that "static" makes your hair stand up. You also may have noticed that your hair sticks to the balloon, a phenomenon commonly known as "static cling."

Forces Between Particles

Opposite charges are positive and negative. Opposite charges attract each other. Like charges are both negative or both positive. Like charges repel each other.

Charged particles may attract or repel each other.

Most materials have no overall charge because they have equal numbers of protons and electrons. When you rub a balloon on your hair, however, electrons from atoms in your hair are transferred to atoms in the balloon. This transfer makes some atoms in your hair positively charged and some atoms in the balloon negatively charged. Because like charges repel, the positively charged strands of your hair spread far away from one another. Opposite charges attract, so the positively charged hair sticks to the negatively charged balloon. Repulsions and attractions due to electric charge are known as electric force. Another name for electric force is the Coulomb force.

MATH CONNECTION

Calculating Force

Coulomb’s law describes how to calculate electric force. This law states that the magnitude of the electric force (Felectric) between two point charges (q1 and q2) is directly related to the product of the charges and inversely related to the square of the distance (d) between them. The Coulomb constant (kC) is a constant used in the calculation of electric force. The equation for Coulomb’s law is:

COLLABORATE

As charge increases, electric force increases. However, if the distance between two charges doubles, electric force decreases by a factor of four. How does the equation for this law demonstrate these relationships between charge, distance, and force?

Glass tubes are placed open-end first into a tub of water. The water rises up the tubes, above the surface of the water in the tub.

Capillary action

Attractive forces exist between protons and electrons in atoms. In ionic compounds, strong attractive forces hold ions tightly together, which explains why these compounds have high melting points. Molecular compounds tend to have relatively low melting points, but attractive forces can still exist between molecules.

HANDS-ON ACTIVITY

Modeling Intermolecular Forces

Models can help explain how interactions at the small scale affect properties of substances at the larger scale. In this activity, you will use magnets to model the strength of forces between molecules. Forces between molecules are known as intermolecular forces. Typically, as the strength of the forces between molecules increases, the energy required to change the state of that substance also increases.

Download Activity Worksheet

MATERIALS

indirectly vented chemical splash goggles

boxes of labeled “molecules,” each containing magnets of a different strength

Eye Protection

SAFETY INFORMATION

Wear indirectly vented chemical splash goggles during all segments of the activity.

CARRY OUT THE INVESTIGATION

Make a table in your Evidence Notebook to record observations of the strengths of intermolecular forces between “molecules” in each of the five labeled boxes.

Use the magnets in each box to model the intermolecular forces between these molecules. Note the amount of force you need to pull each set of magnets apart, and record your observations.

Draw a scale of intermolecular force strength in your Evidence Notebook. Label the left end Weakest and the right end Strongest. Plot the formulas and names for the five molecules you modeled in the correct order along the scale.

DRAW CONCLUSIONS

In your Evidence Notebook, rank the molecular substances you modeled from lowest boiling point to highest. Give evidence for your claim, and explain your reasoning.

Uneven Molecular Charges

In a nonpolar covalent bond, the electron cloud is spread evenly around the two nuclei. In a polar covalent bond, the radius of the electron cloud is larger around one nucleus than the other.

In a nonpolar covalent bond, the electron cloud is evenly dispersed. In a polar covalent bond, it is not.

Why do different molecular compounds exhibit different intermolecular forces? The answer has to do with the type of atoms in a molecule and how they are arranged. Recall that electronegativity is the tendency of an atom to pull electrons toward itself. When two atoms of the same element form a covalent bond, such as that in Cl2, the bonding electrons are evenly shared between the two atoms. This is known as a nonpolar covalent bond. When atoms of two different elements form a covalent bond, such as that in ICl, the atom with the higher electronegativity attracts the bonding electrons more strongly than does the other atom. This is known as a polar covalent bond. This uneven distribution of charges in a molecule is known as polarity.

In a polar molecule, such as ICl, one end of the bond has a partial negative charge, and the other end has a partial positive charge. These two ends are called poles, and a molecule with two poles is said to be a dipole. Magnets can be used to model dipoles because a magnet has a north pole and a south pole. 

In this model, a large ball marked delta plus and a smaller ball marked delta minus are joined by a rod. An arrow shows the direction of the dipole, from delta plus to delta minus.

Iodine chloride is a dipole.

In the diagram shown here, a model of iodine monochloride, ICl, is depicted. Its dipole is represented by an arrow with a head that points toward the negative pole and a crossed tail near the positive pole. Partial charges are represented by the lowercase Greek letter delta, δ. A partial positive charge is shown as δ+, and a partial negative charge is shown as δ–.

The polarity of diatomic molecules such as ICl is determined by just one bond. For molecules that contain more than two atoms, polarity is determined by both the polarity of the individual bonds and the three-dimensional arrangement of the molecule. How the three-dimensional arrangement of dipoles in a molecule affects the overall polarity of the molecule is shown in the table. 

Water and ammonia are polar molecules, whereas carbon tetrachloride and carbon dioxide are nonpolar.

In a water molecule, dipoles are directed toward the partial-negative oxygen atom, away from the 2 partial-positive hydrogen atoms.

In an ammonia molecule, dipoles are directed toward the partial-negative nitrogen atom, away from the 3 partial-positive hydrogen atoms.

In a carbon tetrachloride atom, dipoles are directed away from the central carbon atom toward the 4 surrounding chlorine atoms.

In a carbon dioxide atom, dipoles are directed away from the central carbon toward the 2 oxygen atoms on each side.

Water, H2O

Ammonia, NH3

Carbon tetrachloride, CCl4

Carbon dioxide, CO2

The water molecule is bent, so its bond polarities combine to give one end of the molecule a partial positive charge and the other end of the molecule a partial negative charge. Ammonia has a pyramid shape, so it is also a polar molecule. In carbon tetrachloride and carbon dioxide, the bond polarities extend equally and symmetrically in different directions, canceling each other’s effect. Therefore, these molecules are nonpolar.

A water molecule has two dipoles, and because the molecule is bent, the arrangement of the bonds is not symmetrical. In addition, there are two unshared electrons on the oxygen atom in a water molecule. Therefore, the water molecule is highly polar. It behaves as if it has two centers of charge, one positive and one negative. Carbon dioxide, by contrast, is nonpolar, even though it has two polar bonds. The carbon dioxide molecule is symmetrical, so the two dipoles cancel each other out.

COLLABORATE

Think back to the question about why water exhibits capillary action. With a partner, make a claim for how this phenomenon is related to the polarity of water molecules.

Dipole-Dipole Forces

You have seen that in the polar molecule iodine chloride, the highly electronegative chlorine atom has a partial negative charge, causing the iodine atom to have a partial positive charge. As a result, the negative and positive ends of neighboring iodine chloride molecules attract each other. In this diagram, these attractive forces are shown as arrows.

A diagram shows four iodine monochloride formula units. The units are arranged two over two, so that each partially positive iodine atom is next to a partially negative chlorine atom. Arrows point from each atom to the oppositely charged atom in the adjacent formula unit.

The arrows show the dipole-dipole forces between the positive and negative ends of neighboring ICl molecules. These forces can be modeled by magnets because the south pole of a magnet is attracted to the north pole of other magnets.

When a liquid is heated, energy is added to the system. The kinetic energy of the liquid’s molecules increases, and they move faster. As the temperature approaches the boiling point, the molecules move fast enough to overcome the attractive forces between molecules. They pull away from each other and enter the gaseous state. Boiling point is a good measure of the attractive forces between molecules of a liquid. The stronger the forces are between molecules, the higher the boiling point will be.

A polar molecule also can induce the formation of a dipole in a nonpolar molecule by temporarily attracting the electrons in the nonpolar molecule. This results in a short-term intermolecular force. For example, the positive pole of a polar water molecule causes a temporary change in the electron distribution of an adjacent nonpolar O2 molecule. The temporary negative pole induced in the side of the O2 molecule closest to the water molecule is attracted to the positive pole of the H2O molecule. This shift of electrons in the oxygen molecule then causes an induced positive pole on the opposite side of the oxygen molecule.

As separate molecules, water has a dipole between the oxygen atom and hydrogen atoms, but the two oxygen atoms in the oxygen molecule do not. If the oxygen molecule comes near the water molecule, it can induce a dipole in the oxygen molecule.

Dipole-induced dipole interaction

Hydrogen Bonding

Some dipole-dipole interactions can be especially strong. For example, in some hydrogen-containing compounds such as hydrogen fluoride (HF), water (H2O), and ammonia (NH3), a special kind of dipole-dipole interaction exists.

Boiling Points and Bonding Types

Bonding Type Substance bp (1 atm, °C)

Nonpolar-covalent (molecular) H2

O2

Cl2

Br2

CH4

CCl4

C6H6 −253

−183

−34

59

−162

77

80

Polar-covalent (molecular) PH3

NH3

H2S

H2O

HF

HCl

ICl −88

−33

−60

100

20

−85

97

Ionic NaCl

MgF2 1465

2239

Metallic Cu

Fe

W 2567

2861

5660

You may have noticed in the table that some hydrogen-containing compounds have unusually high boiling points. These compounds have two things in common. First, they all contain a hydrogen atom. Second, the hydrogen atom is bonded to a highly electronegative atom that has pulled hydrogen’s bonding electron almost completely away. Thus, the hydrogen atom is left with a strong partial positive charge.

Molecules that contain a hydrogen atom bonded to a highly electronegative atom—fluorine, oxygen, or nitrogen—are strongly polar. Particularly strong dipole-dipole forces exist between molecules of these compounds. The name hydrogen bonding is given to the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom (and thus is positively charged) is attracted to a partial negative charge on a nearby molecule. A hydrogen bond is usually represented by a dotted line that connects the hydrogen-bonded hydrogen to the partial negative charge on another molecule.

Analyzing the Properties of Water

Evidence of surface tension of different liquids ranges from a perfect bead on a surface, to a flattened pool with shallow sides.

Different liquids exhibit different amounts of surface tension.

Water is a substance with many unusual properties given its relatively small molecular mass and size. For one, it has an unusually high boiling point. In addition, water adheres, or “sticks” to surfaces such as glass. This explains why water appears to climb up narrow tubes in the phenomenon known as capillary action. Cohesion between water molecules causes water to form a bubbled-up shape when it is dropped onto some surfaces. The ability of the surface of a liquid to form a “skin” is known as surface tension. This property of water allows some smaller insects to walk easily on its surface.

If you have ever frozen a full bottle of water, you have discovered that, unlike other substances, water expands when it freezes. Like many of water’s unique properties, this is related to the formation of hydrogen bonds.

In solid water, each water molecule bonds with 3 others, making hexagonal patterns. In liquid water, water molecules are arranged more randomly. The number of bonds between molecules ranges from 0 to 3.

Water molecules are arranged differently in solid water than in liquid water.

An iceberg floats in water, with most of the iceberg underwater.

Icebergs float on liquid water.

When water freezes, the molecules lose kinetic energy and slow down, so more hydrogen bonds form between them. The water molecules form a network structure in which each water molecule is held away from nearby molecules at a fixed distance. Hydrogen bonds are constantly being formed and broken between molecules in liquid water. In order for liquid water to boil and become a gas, hydrogen bonds between the water molecules must be broken.

STRUCTURE AND FUNCTION

Living Systems

Hydrogen bonds occur between sugars in a DNA molecule, forming steps in a spiraling ladder shape.

DNA

Hydrogen bonds play a very important role in living organisms. For example, DNA molecules are held together by hydrogen bonds. A DNA molecule looks like a long twisted ladder, with two long chains of sugar molecules and phosphate groups making up the sides of the ladder and nitrogen bases sticking into the center like steps of the ladder. These nitrogen bases are held together by millions of hydrogen bonds, which stabilize the DNA molecule. Because individual hydrogen bonds are weak, some break to allow the chains to separate during DNA replication and protein synthesis.

LANGUAGE ARTS CONNECTION

Research the structure of DNA. Why is it important to have hydrogen bonds rather than ionic or covalent bonds holding the two chains of DNA together? Develop a presentation answering this question and explaining how the different types of chemical bonds in a DNA molecule relate to its structure and function.

London Dispersion Forces

In all atoms, electrons are in constant motion. As a result, the electron distribution may become slightly uneven at any instant. While this uneven distribution of charge lasts for only a very short period of time, it creates a positive pole in one part of an atom or molecule and a negative pole in another part. This temporary dipole does not affect molecules or atoms that are far away, but it can induce a dipole in a nearby neighbor. The two atoms or molecules are held together for an instant by the weak attraction between the temporary dipoles. These weak intermolecular attractions that result from the constant motion of electrons are called London dispersion forces. All London forces are temporary because electrons are in constant motion and so quickly move to other locations. Unlike hydrogen bonds, London dispersion forces exist between atoms or molecules of any kind, including nonpolar molecules and noble gas atoms.

In a momentary dipole of a helium atom, the 2 electrons are on one side of the nucleus. This induces a dipole in a neighboring atom, with electrons of one atom attracted to the nucleus of the other.

When an instantaneous, temporary dipole develops in a helium atom, it induces a dipole in a neighboring atom.

The strength of London forces increases as the number of electrons in the interacting atoms or molecules increases. So, London dispersion forces increase with increasing atomic or molar mass. This trend is evident in the halogen group of the periodic table. While the lightest halogens, fluorine and chlorine, are gases at room temperature, the next larger, bromine, is a liquid. The next larger still, iodine, is a solid. Materials Science and Design

An apparatus tests a rectangular piece of screen glass, causing the glass to bend but it does not break.

 Testing the flexibility of screen glass

Have you ever wondered how smartphone glass was developed? Engineers are always trying to improve materials. Materials science is the scientific study of the properties and applications of materials. In developing flexible phone glass, for example, scientists and engineers not only had to study the properties of the glass, but they had to find ways to deliver needed quantities of the glass to the manufacturer. Flexible glass can be delivered in rolls and then cut into pieces.

The Structure of Materials

Materials scientists develop new materials and optimize the performance of materials that already exist. These scientists investigate how factors at the atomic scale affect the properties of materials at the macroscopic scale. Materials are often subdivided into five major categories: metals, ceramics, semiconductors, polymers, and composites.

Metals

An artificial hip joint consists of a titanium metal ball attached to the top of the leg bone. The ball fits into the hip bone.

Titanium metal is used for artificial hips.

For thousands of years, humans have used metals for many purposes from tools to jewelry. In fact, historians talk about the transitions from the Stone Age to the Bronze or Iron Ages when discussing ancient human history. Today, materials scientists are still finding ways to make and use new metal products more efficiently. In addition, scientists can combine different metals to form alloys such as steel that have different properties from their components. All metals exhibit metallic bonding where valence electrons are shared by the entire solid. Thus, they share properties of thermal and electrical conductivity, malleability, ductility, and the ability to reflect light from their shiny surfaces. These properties allow us to develop medical implants, lighter airplanes, and better methods of communications.

Ceramics

Small glass rings surround a portion of a utility wire.

Porcelain or glass insulators may protect utility poles from high voltages.

A ceramic is neither metallic nor organic. Most ceramics are hard and chemically non-reactive, and they usually are formed by heating other substances. Some ceramics are conductors, meaning they transmit electricity and heat, while others are not. Glass, pottery, clay, bricks, tiles, and cement are typical ceramics. They are used to make such diverse products as spark plugs, artificial joints, body armor, skis, cooktops, and race car brakes.

Semiconductors

A person dressed in full protective gear examines computer chips in a clean room.

A clean room at a computer-chip production facility

Semiconductors are materials that have electrical conductivity values between that of a conductor, such as copper, and an insulator, such as glass. Their resistance decreases as their temperature increases. Thus, they are not effective conductors at low temperatures, but they do conduct electrical currents at temperatures above room temperature. This property makes them valuable in advanced electronics and communications, where their conducting properties may be altered in useful ways by the controlled introduction of impurities. Silicon, the most widely used semiconductor, makes up chips in electronic devices. Chip production must be done in clean rooms under controlled conditions with low concentrations of dust particles and other unwanted impurities and at a specific humidity. Semiconductors are also used to make solar cells because they absorb light and generate a current. They are used to make lasers and LEDs because they can emit colored light when they contain certain impurities.

Polymers

Think about how many different types of plastic you use every day. They are invaluable to everyday life, but disposing of them responsibly is not always easy. Could optimizing the properties of plastics make it easier to recycle them? Most plastics are made of polymer-based materials. Polymers are compounds composed of very large molecules. These molecules are made up of smaller subunits called monomers. Polymers are everywhere—from storage containers to biomedical items such as contact lenses. DNA, spider silk, and proteins are natural polymers. The hydrocarbon monomers that make plastics come from fossil fuels. Hydrocarbons are compounds that contain only carbon and hydrogen.

Four types of polymer structures include linear chains, branched chains, cross-linked chains, and networks. In networks, loops of molecules are connected.

Polymer structures

The properties of different types of plastics result from their molecular structure. For example, a linear polymer is a long chain of subunits linked together. Because linear chains can stack closely together, materials made of this type of polymer, such as nylon, have relatively high densities, strengths, and melting points. 

Branched polymers have groups of subunits branching off from a long polymer chain. Depending on how these side chains branch off, intermolecular forces may exist between them. For example, the polymers in low-density polyethylene (LDPE) are more highly branched than those in high-density polyethylene (HDPE). As a result, the polymers in LDPE cannot stack as neatly together, and the plastic is more flexible than HDPE. However, plastics made of LDPE are not as strong as those made of HDPE.

Cross-linked polymers form long chains, either branched or linear, that develop covalent bonds between the polymer molecules. These bonds are much stronger than the intermolecular forces that hold other polymers together. Thus, cross-linked polymers such as synthetic rubber are strong and stable. Finally, network polymers, such as epoxy adhesives, form so many interconnections between chains that an entire sample of the polymer may be a single molecule. These polymers are strong and heat resistant.

A thermoplastic container keeps its shape when placed in an oven. Other plastics deform due to heat.

Thermoplastics

Thermoplastics are polymer-based materials that melt when heated. Their properties are influenced by electrostatic forces between their molecules. Thermoplastics are formed by applying heat and pressure to the monomer subunits. The length of the polymer, which influences properties such as toughness and melt temperature, can be controlled. The melt temperature of a thermoplastic affects how easily it can be recycled.

After the polymers in thermoplastics form, the chains are like long, tangled bundles of spaghetti. There are no covalent bonds between chains, but there are weak attractive forces that exist between neighboring chains. These forces become stronger when the plastic cools and weaker when it is heated. The shape of the polymer molecules also influences the final material because it affects how densely the molecules will pack together.

INFLUENCE OF ENGINEERING, TECHNOLOGY, AND SCIENCE

Composite Materials in Prosthetic Limbs

In a composite, different materials are combined to form a new material with its own unique properties. One component of a composite typically surrounds and binds the other component. The original materials and the new material all exist separately in the final structure. The first composite made was fiberglass, composed of glass fibers and plastic. Glass is strong but brittle. The plastic holds glass fibers together to form a light, strong, and flexible composite. Other modern composites include wood laminates used for flooring, reinforced concrete, and even waterproof clothing.

A runner with a carbon-fiber prosthetic leg leaps off the starting block.

Carbon fiber is a composite material that makes prosthetic limbs lightweight and durable.

Composite materials have helped revolutionize many products, including vehicles, sports equipment, and prosthetic limbs. For example, the “blade leg” shown in the photo typically contains carbon fiber material. This composite material was originally developed for use in aerospace technologies, but its use has expanded quickly due to its desirable properties. The advantages of using carbon fiber over more traditional materials include increased flexibility, greater durability and strength, and reduced weight.

Carbon fiber is made by embedding fibers made from carbon in a resin. Different forms of carbon fiber have different properties based on the orientation of the fibers and the type of resin used. Controlling these aspects of the material allows scientists to develop carbon fibers with varying degrees of strength, weight, and stiffness. The development of new composite materials is likely to keep changing the way we use materials in our daily lives.

LANGUAGE ARTS CONNECTION

Research composite materials used in the construction of prosthetic limbs. Make a pamphlet explaining the costs and benefits of these materials in terms of affordability, durability, and environmental impact. In addition, explain how the properties of these materials at the larger scale are related to their properties at the atomic scale.

ENGINEERING

Optimizing Material Design

As was mentioned at the beginning of this lesson, fog collectors could provide an alternative source of fresh water in dry areas. This technology works best in areas with frequent foggy periods. This includes coastal areas where fog is moved toward the land by wind, similar to many parts of California. Fog-collecting technology also has been used in other parts of the world, including Chile, Peru, and Guatemala.

Dozens of small, rectangular, fog-harvesting nets are arranged vertically on a coast.

These nets are part of a fog-harvesting project in California. 

The nets in the photo are part of a fog-harvesting project on East Anacapa Island in California. The material used in nets like these is usually nylon, polyethylene, or polypropylene. The density of the mesh can be varied to capture more or less water. Droplets that collect on the mesh may drip into a gutter or similar structure that channels the water into a storage tank. Dust, debris, and algae must be regularly removed from nets, and storage tanks must be maintained to prevent fungi and bacterial growth.

Droplets of water collect on the back of a Namib desert beetle.

The Namib desert beetle can harvest water from the air.

Researchers are taking inspiration from living things to design water-collecting materials. For example, the Namib desert beetle survives in its desert home in southern Africa by drinking water that condenses on its hard, bumpy wing covers in early morning fog. A microscopic examination of the beetle’s wings shows that they are covered with tiny bumps and grooves that appear to be composed of different materials. The bumps are made of a material that attracts water from the air, and the material that makes up the grooves repels the water. Thus, the water runs along the grooves and is channeled into the beetle’s mouth. Engineers have used this observation to develop a new material that mimics the way the beetle’s water-gathering system works. One part of the material attracts and collects water from the air. Another part of the material repels this water, which runs off the material and can be collected.

Could fog collection be an answer to problems associated with water scarcity in areas such as California? This technology has many factors that must be considered before it is installed in an area. For example, fog is often seasonal, so fog may not be available year-round. The technology also works best at particular heights and slopes. In addition, it is not unusual for a person in the United States to use 80 gallons of water per day. This amount does not include the amount of water used to grow crops or manufacture products. So, it might be asked whether enough water is produced to make the process worthwhile. The water must also be transported and distributed.

After developing a new material, such as a water-collecting fabric, materials scientists test and analyze the material to make sure it has the desired properties. An engineer may use a decision matrix to determine how well a design meets important criteria. In a decision matrix, each criterion is given a number, or weight, based on how important that criterion is. For example, in the hypothetical decision matrix below, durability is given a weight of 4, so, it is the most important criterion. Limiting algae growth is the least important, so it has a weight of 1. Each design is rated based on how well it meets the chosen criteria. The score for each criterion in a design is then multiplied by its respective weight, and the products are totaled. Engineers may choose to take the design with the highest score to the next phase in the engineering design process, or they may choose to brainstorm new ideas if no designs meet the requirements satisfactorily.

Decision matrix for fog-collecting material

Design Criteria Weight Design 1 Design 2 Design 3

Durability 4 5 1 4

Water collected 3 2 3 4

Cost 2 1 2 1

Algae growth 1 1 4 0

Total Points 29 21 30

A matrix helps engineers consider tradeoffs of different designs. Materials scientists optimize materials for efficiency. They also optimize the processes that produce those materials. After repeated testing of a material, scientists may start the design process over again. If the manufacturing process is inefficient or too costly, a new process may be developed. The optimization process constantly considers these tradeoffs. Organic Chemistry

Could you use your knowledge of intermolecular forces to help develop a cure for a disease? One person who is doing just that is James Nowick, a professor and organic chemist. Organic chemistry is the field of study that focuses on the chemistry of carbon-based molecules, especially those in living things. An organic chemist may study the structure and function of proteins, carbohydrates, DNA, or lipids. A person in this field might want to learn how these molecules are produced in the body, how they interact with other molecules, or how they affect a person’s health.

Understanding the structure and function of proteins is an important part of finding cures for diseases such as Alzheimer’s disease. Professor Nowick studies proteins involved in Alzheimer’s and other neurodegenerative diseases. His research group is developing synthetic molecules that are similar in structure and function to these proteins. The purpose of developing these synthetic proteins is to model interactions between different parts of molecules. For example, a beta-pleated sheet is a zig-zag-shaped structure found in some proteins. When two beta-pleated sheets are near each other, hydrogen bonds form between the polar carbon-oxygen and nitrogen-hydrogen groups on the two sheets.

By using synthetic proteins as models, Nowick’s group is able to learn more about the forces that hold these molecules together and how changes in these interactions might lead to disease. The techniques his team uses include molecular modeling, spectroscopy, and x-ray crystallography. These tools allow the group to understand how the building blocks of proteins interact and how they could possibly manipulate those interactions. The general process Nowick’s group uses typically involves making new molecules that they think will interact through hydrogen bonding and other intermolecular forces. They can then analyze how the proteins fold, interact with other molecules, and operate in the human body.

James Nowick holds a small model of an organic molecule.

James Nowick studies a model of an organic molecule.

James Nowick has been honored many times for his teaching, mentorship, and contributions to his community. He identifies as part of the LGBTQ+ community and has worked with organizations such as the Gay and Transgender Chemists and Allies subdivision of the American Chemical Society. This group works to promote inclusion, advocacy, and collaboration among LGBTQ+ chemists. Nowick’s contributions to science and his community are numerous. His work will likely continue to spur other important discoveries in this field and inspire others to pursue careers in science.

CHEMISTRY IN YOUR COMMUNITY 

Research a scientist who works in the field of organic chemistry or biochemistry. Develop a profile for this person that explains the topics they study, what questions they hope to answer through their research, and how they collaborate with others in their field. Discuss the real-world applications of their research, and, if applicable, explain how intermolecular forces are related to their area of study.