Objectives |
Structure of Matter
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Define atom, molecule and ion.
Outline a bond as a force of
attraction between particles.
Draw an equilibrium position of a
particle in a bond using a general potential energy–separation curve.
Define an element, compound,
pure substance, mixture, alloy
and composite.
Bonding
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Draw and describe the primary bonds:
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ionic: opposing charges of ions
hold the crystal (eg NaCl) together in a lattice. Ions can often be
separated easily in water but the electrons stay attached to their
respective ions inside the crystal.
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covalent: outer electrons of
some atoms shared between the nuclei. Each pair of electrons shared is
called a covalent bond.
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metallic: outer electrons are
freer and can flow through the crystalline structure. Bonding is caused by
attraction between the positively charged metal atom nuclei and the
negatively charged cloud of free electrons, and is spread throughout the
lattice—“Positively charged nuclei in a sea of electrons”.
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State \relative strengths of
primary bonds: ionic > metallic > covalent.
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Describe secondary bonds: weak
forces of attraction between molecules
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Explain network covalent (giant)
structure, with reference to diamond and sand (SiO 2).
Describe a crystal as a regular
arrangement of particles (atoms, ions or molecules).
Define an
amorphous material and a fiber structure.
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Amorphous materials: no
regular structures or crystal. Short range order may occur as far as next
neighbor atoms. The general appearance of amorphous materials is glossy
and they can occur in ceramics, polymers and metals.
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Fibers: length-to-thickness
ratio of at least 80 but are generally much longer. Textile fibers
and food are made up of polymers.
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Explain melting in terms of the
behavior of particles and the bonding.
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Explain boiling in terms of the
behavior of particles and the bonding.
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Discuss the significance of pure
substances melting at a fixed temperature, and mixtures softening over a
range of temperatures before melting.
The IB Properties/Bonding Matrix
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Describe the relative values of the
materials in the IB properties/bonding
matrix in terms of their bonding.
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Analyze data related to the
IB properties/bonding matrix.
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Evaluate the importance of the
IB properties/bonding matrix in a given
design context.
The Properties of Metals and Alloys
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State that metals (pure or alloyed)
exist as crystals.
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Draw and describe
what is meant by grain size.
Explain how grain size can be
controlled and modified
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rate of
cooling of molten metal: Alters grain
size and formation of various phases within the metal.
Slow
cooling allows larger grains to form; rapid cooling produces smaller grains.
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heat
treatment after solidification: allows material to diffuse between neighboring grains and the grain
structure to change. Directional properties in the structure may
be achieved by selectively cooling one area of the solid.
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Explain in words and diagrams how
metals work harden after being plastically deformed.
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Explain in words and diagrams the
effect of alloying on malleability and ductility.
The Properties of Thermoplastics and Thermosets
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Draw and describe the structure and
bonding of a thermoplastic.
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Explain the effect of load on a
thermoplastic, with reference to orientation of chains.
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Explain the reversible effect of
temperature on a thermoplastic, with reference to orientation of chains.
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Draw and describe the structure and
bonding of a thermoset.
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Explain the non-reversible effect
of temperature on a thermoset.
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Discuss the properties and uses of
two thermoplastics including polypropene.
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Discuss the properties and uses of
two thermosets including polyurethane.
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Discuss the importance of the
properties of plastics on the recycling of plastics.
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Evaluate the importance of the
properties of thermoplastics and thermosets on product design.
The Properties of Composite Materials
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State that composites are a
combination of two or more materials which are bonded together to improve
their mechanical, physical, chemical or electrical properties.
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Describe the structure of wood as a
natural composite material.
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Discuss in outline the evolution of
synthetic composite materials
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wattle-and-daub
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mortar
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papier mâché
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reinforced concrete glass reinforced plastic (GRP)
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carbon
reinforced plastic (CRP)
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high temperature superconductors.
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Outline the structure of Kevlar TM
(aramid) fiber.
Outline two examples where Kevlar TM
fibers twisted into ropes and
woven
into sheets (mats) are used.
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Rope—light, non-stretch ropes
used in sailing boats.
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Sheets—sails yachts, bullet
resistant vests
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composite structures with resin —motor racing cars.
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Explain why KevlarTM
is suited to these applications with reference to its tensile
strength, elasticity and water resistance.
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Evaluate the importance of the
properties of composite materials in a design context.
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