Unit 2 – Section D

Materials: Designing for Desired Properties

HW 1

Read and take notes on D.1 (starting on pg. 184) AND answer questions in D.2, 1-4 on pg 187.

D.1 Structure & Properties: AllotropesMaterial 1

• Black solid• Soft & “greasy” to

the touch• Leaves black marks

on paper• Useful lubricant• Good electrical

conductor• Pennies per gram

Material 2 • Colorless, glasslike

solid• Extremely hard• Useful as abrasive• Electrical insulator• $50-20,000 per

gram

Material 3 • Fine, powdery solid• Extremely round

molecules• Discovered in 1985• The cost, while

dropping is between $170 - $3,000 per gram

D.1 Structure & Properties: Allotropes(continued)

While all three distinctly different substances – they are the same element.

Allotropes are all different forms of an element that have distinctly different physical or chemical properties.

D.1 Structure & Properties: Allotropes(continued)

GRAPHITE • Black solid• Soft & “greasy” to

the touch• Leaves black marks

on paper• Useful lubricant• Good electrical

conductor• Pennies per gram

DIAMOND • Colorless, glasslike

solid• Extremely hard• Useful as abrasive• Electrical insulator• $50-20,000 per

gram

FULLERENES • Fine, powdery solid• Extremely round

molecules• Discovered in 1985• The cost, while

dropping is between $170 - $3,000 per gram

D.1 Structure & Properties: Allotropes(continued)

How do chemists account for the distinctly different physical or chemical properties?

For allotropes, the explanation lies in how the atoms are linked and organized.

D.2 Linking Properties to StructureQ1 – How might the actual structure of diamonds help explain why it is sometimes found in the form of large, single crystals?

A1 – The simple regular structure provides a pattern that can be extended indefinably as long as conditions permit and carbon atoms are available.

D.2 Linking Properties to Structure(continued)

Q2 – What feature of graphite’s structure might account for its usefulness as a lubricant?

Q2 – The planar sheets of graphite can slip past one another easily.

D.2 Linking Properties to Structure(continued)

Q3 – Why are fullerenes powdery as solids rather than composed of large-scale chunks?

Q3 – Fullerenes are essentially small spheres of self-contained carbon atoms; the spheres are not interlinked, so they behave as a powder.

D.2 Linking Properties to Structure(continued)

Q4 – Buckminsterfullerne (C60) can be regarded as a hollow sphere. Chemists have an ability to place atoms inside of these spheres – is there a practical application of this ability?

Q4 – Fullerenes could serve as protective cages to transport medicines within the body.

HW 2

Read and take notes on D.3 (starting on pg. 187) AND answer questions in D.4, 1-3 on pg 190.

D.3 Engineered MaterialsCeramics – clay which is made up of the plentiful material , kaolinite (Al2O3·2SiO2·2H2O) along with Mg+, Na+ & K+ ions has been used by humans to mold and heat into useful products.

D.3 Engineered Materials(continued)

Desirable qualities of ceramics – hardness, rigidity, low chemical reactivity & resistance to wear.

D.3 Engineered Materials(continued)

Plastics – from Greek - capable of being shaped or molded , synthetic carbon-atom chains and rings of hydrogen and other atoms attached. Less dense than metals and can be designed to be “springy”.

D.3 Engineered Materials(continued)

Desirable qualities of plastics – resilient where metals may be dented. Many properties can be customized.

Unfortunately most plastics are made from petroleum a non-renewable resource.

D.4 Alternatives to MetalsQ1 – a. Select 4 uses of Cu from the list contained in Figure 2.18 (pg 138) AND suggest an alternative material that could serve the same purpose? (conventional and possible new material)A1 –

Uses Alternative Uses Alternatives

Household wiring Jewelry

Communication Pots & Pans

Plumbing Shell casings

Roofing Food Prep. Machinery

Coins Auto Radiators

D.4 Alternatives to Metals(continued)

Q2 – Suggest some common metallic items that might be replaced by ceramic or plastic versions then explain in what ways they would be preferable and in what way would the original metal be better?

A2 – •Automobile bumpers•Automobile engines•Plumbing material•Sports gear•Aircraft parts

Ceramics can withstand higher temperatures, but are brittle.

Plastic is more flexible , but not as long lasting in many applications

D.4 Alternatives to Metals(continued)

Q3 – Suppose Ag became as common & inexpensive as Cu. In what uses would Ag most likely replace Cu? Explain.

A3 – In wiring, Ag would be more electrically conductive than Cu. Ag might also replace Cu in coins, since it is less reactive.

HW 3

Preread D.5 Striking It Rich

HW 4

Read and take notes on D.6 (starting on pg. 193)

D.6 Combining Atoms: Alloys & Semiconductors

As we saw in our lab, the immersion of penny in a hot ZnCl2 solution produced a silvery looking penny.

An alloy of zinc & copper called brass.

Alloy is a combination of two or more metals.

D.6 Combining Atoms: Alloys & Semiconductors(continued)

Alloys are also commonly referred to as “solid solutions”

They have a constant, definite ratio of metallic atoms.

EXAMPLES

Ni3Al – low-density, strong - used as a component of jet aircraft engines

Very hard – Cr3Pt – commercial razorblade edges

A special group, including Nb3Sn (niobium-tin) which is a superconductor , conducting electricity without resistance.

D.6 Combining Atoms: Alloys & Semiconductors(continued)

Another type of alloy is one which uses semi-metals in the mixtures.

Silicon is a metalloid used in the production of semiconductors.

Semiconductors allows computers to process digital information.

D.6 Combining Atoms: Alloys & Semiconductors(continued)

Adding impurities to pure silicon dramatically increases its semiconductor properties. P, As, Al are commonly used – this is called doping.

HW 5

Read & take notes on D.7

D.7 Modifying SurfacesCoating – paints varnishes & shellacs are

examples of coatings.

Typically contains a pigment (the color or tint) and a solvent.

D.7 Modifying Surfaces(continued)

Electroplating is causing a redox reaction to occur between a metal and a metal-ion solution.

D.7 Modifying Surfaces(continued)

Half-reaction equations are helpful

Ni2+(aq) + 2 e- Ni(s)

Copy image !

Electrons go to the cathode (where reduction occurs)

The source of the electrons is the anode.

Electroplating requires a power source.

D.7 Modifying Surfaces(continued)

Thin films may be modern materials only one or two atoms or molecules thick.

The array will produce around 5.7 million kilowatt-hours of solar electricity every year, enough to power some 1,900 homes.

HW 6

Preread D.8 Copper Plating

D.8 Copper Plating

HW 7

Answer D.9 More Coin design Considerations – Q 1-3 on pg 203.

Q1 – What properties of alloys make them an attractive option in coin design?

A1 – •Resistance to corrosion•...and oxidation•durability•color

D.9 More Coin Design Considerations

Q2 – Why might simply modifying the coins surface be preferable?

A2 – It may be less expensive.

D.9 More Coin Design Considerations

Q2 – Benefits & drawbacks of using alloys vs. surface modification?

A2 – • Cost•Lack of durability•availability

D.9 More Coin Design Considerations