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Bonding and Properties

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Competition in Product Development

1) between groupsmetal alloys vs. ceramics vs. polymers

e.g. – beverage containers

2) within groups

steel vs. aluminum vs. titanium

e.g. bicycles, autos

3) between producers of the same material

e.g. Alcan vs. Alcoa

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QUESTION ??

What are the designrequirements that need

to be considered forbeverage containers ?

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For any givenproperty, we canthen comparedifferent materials,and choose the bestone(s)

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Question

• What are the factors which control theproperties of materials ?

– Composition – what it is made from – Bonding – Crystal structure – arrangement of atoms – Temperature – Pressure

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Bonding controls

• Melting temperature• Density• Thermal and Electrical Conductivity• Coefficient of Thermal Expansion• Stiffness

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Types of Bonds

• Primary Bonds – Ionic Bonds – Covalent Bonds – Metallic Bonds

• Secondary Bonds – Van der Waals Bonds – Hydrogen Bonds

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Acrobat Document

Bond Energy Diagram

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Ionic Bond

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Ionic Bond Formation

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Covalent Bonds

The formation of a covalent bond – in this case between twohydrogen atoms, making a hydrogen molecule

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Covalent Bonds are Directional

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Metallic Bonds

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Secondary Bonds

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Hydrogen Bonds

From Wikipedia.org

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Bond Energies

Type of Bond Bonding Energy

(kJ/mol) Ionic 600-1500 (strong)

Covalent 100-800 (med.)Primary

Metallic 70-850 (med.)

Van derWaals 10-50 (weak)

Secondary

Hydrogen 10-50 (weak)

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Presence of Bonds

Type of Bond Material

Ionic Covalent Metallic Van der Waals

Metals X X

Polymers X X

Some Ceramics X X

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Bonding Type Substance Bonding Energy(kJ/mol)

MeltingTemperature(deg C)

Ionic NaCl 640 801MgO 1000 2800

Covalent Si 450 1410C (diamond) 713 >3550

Metallic Hg 68 -39 Al 324 660Fe 406 1538W 849 3410

van der Waals Ar 7.7 -189

Cl2 31 -101Hydrogen NH3 35 -78

H2O 51 0

Bonding Energies and MeltingTemperatures

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Presence of Bonds

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Thermal Expansion Coefficient

• Decreases withincrease in bond

energy• Controlled by the

shape of the bondenergy diagram

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Coefficient of Thermal Expansion

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Effect of Temperature onbond spacing

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