A. Materials

A. Materials

Core

A.1 Materials science introduction

Nature of science:

• Improvements in technology - different materials were used for different purposes before the development of a scientific understanding of their properties.

• Patterns in science - history has characterized civilizations by the materials they used: Stone Age, Bronze Age and Iron Age. There are various ways of classifying materials according to desired patterns.

Understandings:

• Materials are classified based on their uses, properties, or bonding and structure.

• The properties of a material based on the degree of covalent, ionic or metallic character in a compound can be deduced from its position on a bonding triangle.

• Composites are mixtures in which materials are composed of two distinct phases, a reinforcing phase that is embedded in a matrix phase.

Applications and skills:

• Use of bond triangle diagrams for binary compounds from electronegativity data.

• Evaluation of various ways of classifying materials.

• Relating physical characteristics (melting point, permeability, conductivity, elasticity, brittleness) of a material to its bonding and structures (packing arrangements, electron mobility, ability of atoms to slide relative to one another).

A.2 Metals and inductively coupled plasma (ICP) spectroscopy

Nature of science:

• Development of new instruments and techniques - ICP spectroscopy, developed from an understanding of scientific principles, can be used to identify and quantify trace amounts of metals.

• Details of data - with the discovery that trace amounts of certain materials can greatly enhance a metal’s performance, alloying was initially more of an art than a science.

Understandings:

• Reduction by coke (carbon), a more reactive metal, or electrolysis are means of obtaining some metals from their ores.

• The relationship between charge and the number of moles of electrons is given by Faraday’s constant, F.

• Alloys are homogeneous mixtures of metals with other metals or non-metals.

• Diamagnetic and paramagnetic compounds differ in electron spin pairing and their behaviour in magnetic fields.

• Trace amounts of metals can be identified and quantified by ionizing them with argon gas plasma in Inductively Coupled Plasma (ICP) Spectroscopy using Mass Spectroscopy ICP-MS and Optical Emission Spectroscopy ICP-OES.

Applications and skills:

• Deduction of redox equations for the reduction of metals.

• Relating the method of extraction to the position of a metal on the activity series.

• Explanation of the production of aluminium by the electrolysis of alumina in molten cryolite

• Explanation of how alloying alters properties of metals.

• Solving stoichiometric problems using Faraday’s constant based on mass deposits in electrolysis.

• Discussion of paramagnetism and diamagnetism in relation to electron structure of metals.

• Explanation of the plasma state and its production in ICP-MS/OES.

• Identify metals and abundances from simple data and calibration curves provided from ICP-MS and ICP-OES.

• Explanation of the separation and quantification of metallic ions by MS and OES.

• Uses of ICP-MS and ICP-OES.

A.3 Catalysts

Nature of science:

• Use of models - catalysts were used to increase reaction rates before the development of an understanding of how they work. This led to models that are constantly being tested and improved.

Understandings:

• Reactants adsorb onto heterogeneous catalysts at active sites and the products desorb.

• Homogeneous catalysts chemically combine with the reactants to form a temporary activated complex or a reaction intermediate.

• Transition metal catalytic properties depend on the adsorption/absorption properties of the metal and the variable oxidation states.

• Zeolites act as selective catalysts because of their cage structure.

• Catalytic particles are nearly always nanoparticles that have large surface areas per unit mass.

Applications and skills:

• Explanation of factors involved in choosing a catalyst for a process.

• Description of how metals work as heterogeneous catalysts.

• Description of the benefits of nanocatalysts in industry.

A.4 Liquid crystals

Nature of science:

• Serendipity and scientific discoveries - Friedrich Reinitzer accidently discovered flowing liquid crystals in 1888 while experimenting on cholesterol.

Understandings:

• Liquid crystals are fluids that have physical properties (electrical, optical and elasticity) that are dependent on molecular orientation to some fixed axis in the material.

• Thermotropic liquid-crystal materials are pure substances that show liquid-crystal behaviour over a temperature range.

• Lyotropic liquid crystals are solutions that show the liquid-crystal state over a (certain) range of concentrations.

• Nematic liquid crystal phase is characterized by rod shaped molecules which are randomly distributed but on average align in the same direction.

Applications and skills:

• Discussion of the properties needed for a substance to be used in liquid-crystal displays (LCD).

• Explanation of liquid-crystal behaviour on a molecular level.

A.5 Polymers

Nature of science:

• Advances in technology - as a result of advances in technology (X-ray diffraction, scanning tunnelling electron microscopes, etc), scientists have been able to understand what occurs on the molecular level and manipulate matter in new ways. This allows new polymers to be developed.

• Theories can be superseded—Staudinger's proposal of macromolecules made of many repeating units was integral in the development of polymer science.

• Ethics and risk assessment - polymer development and use has grown quicker than an understanding of the risks involved, such as recycling or possible carcinogenic properties.

Understandings:

• Thermoplastics soften when heated and harden when cooled.

• A thermosetting polymer is a prepolymer in a soft solid or viscous state that changes irreversibly into a hardened thermoset by curing.

• Elastomers are flexible and can be deformed under force but will return to nearly their original shape once the stress is released.

• High density polyethene (HDPE) has no branching allowing chains to be packed together.

• Low density polyethene (LDPE) has some branching and is more flexible.

• Plasticizers added to a polymer increase the flexibility by weakening the intermolecular forces between the polymer chains.

• Atom economy is a measure of efficiency applied in green chemistry.

• Isotactic addition polymers have substituents on the same side.

• Atactic addition polymers have the substituents randomly placed.

Applications and skills:

• Description of the use of plasticizers in polyvinyl chloride and volatile hydrocarbons in the formation of expanded polystyrene.

• Solving problems and evaluating atom economy in synthesis reactions.

• Description of how the properties of polymers depend on their structural features.

• Description of ways of modifying the properties of polymers, including LDPE and HDPE.

• Deduction of structures of polymers formed from polymerizing 2-methylpropene.

A.6 Nanotechnology

Nature of science:

• Improvements in apparatus - high power electron microscopes have allowed for the study of positioning of atoms.

• The need to regard theories as uncertain - the role of trial and error in the development of nanotubes and their associated theories.

• “The principles of physics, as far as I can see, do not speak against the possibility of manoeuvring things atom by atom. It is not an attempt to violate any laws; it is something, in principle, that can be done; but in practice, it has not been done because we are too big.” - Richard Feynman, Nobel Prize winner in Physics

Understandings:

• Molecular self-assembly is the bottom-up assembly of nanoparticles and can occur by selectively attaching molecules to specific surfaces. Self-assembly can also occur spontaneously in solution.

• Possible methods of producing nanotubes are arc discharge, chemical vapour deposition (CVD) and high pressure carbon monoxide (HIPCO).

• Arc discharge involves either vaporizing the surface of one of the carbon electrodes, or discharging an arc through metal electrodes submersed in a hydrocarbon solvent, which forms a small rod-shaped deposit on the anode.

Applications and skills:

• Distinguishing between physical and chemical techniques in manipulating atoms to form molecules.

• Description of the structure and properties of carbon nanotubes.

• Explanation of why an inert gas, and not oxygen, is necessary for CVD preparation of carbon nanotubes.

• Explanation of the production of carbon from hydrocarbon solvents in arc discharge by oxidation at the anode.

• Deduction of equations for the production of carbon atoms from HIPCO.

• Discussion of some implications and applications of nanotechnology.

• Explanation of why nanotubes are strong and good conductors of electricity.

A.7 Environmental impact—plastics

Nature of science:

• Risks and problems - scientific research often proceeds with perceived benefits in mind, but the risks and implications also need to be considered.

Understandings:

• Plastics do not degrade easily because of their strong covalent bonds.

• Burning of polyvinyl chloride releases dioxins, HCl gas and incomplete hydrocarbon combustion products.

• Dioxins contain unsaturated six-member heterocyclic rings with two oxygen atoms, usually in positions 1 and 4.

• Chlorinated dioxins are hormone disrupting, leading to cellular and genetic damage.

• Plastics require more processing to be recycled than other materials.

• Plastics are recycled based on different resin types.

Applications and skills:

• Deduction of the equation for any given combustion reaction.

• Discussion of why the recycling of polymers is an energy intensive process.

• Discussion of the environmental impact of the use of plastics.

• Comparison of the structures of polychlorinated biphenyls (PCBs) and dioxins.

• Discussion of the health concerns of using volatile plasticizers in polymer production.

• Distinguish possible Resin Identification Codes (RICs) of plastics from an IR spectrum.

Additional higher level

A.8 Superconducting metals and X-ray crystallography

Nature of science:

• Importance of theories - superconducting materials, with zero electrical resistance below a certain temperature, provide a good example of theories needing to be modified to fit new data. It is important to understand the basic scientific principles behind modern instruments.

Understandings:

• Superconductors are materials that offer no resistance to electric currents below a critical temperature.

• The Meissner effect is the ability of a superconductor to create a mirror image magnetic field of an external field, thus expelling it.

• Resistance in metallic conductors is caused by collisions between electrons and positive ions of the lattice.

• The Bardeen-Cooper-Schrieffer (BCS) theory explains that below the critical temperature electrons in superconductors form Cooper pairs which move freely through the superconductor.

• Type 1 superconductors have sharp transitions to superconductivity whereas Type 2 superconductors have more gradual transitions.

• X-ray diffraction can be used to analyse structures of metallic and ionic compounds.

• Crystal lattices contain simple repeating unit cells.

• Atoms on faces and edges of unit cells are shared.

• The number of nearest neighbours of an atom/ion is its coordination number.

Applications and skills:

• Analysis of resistance versus temperature data for Type 1 and Type 2 superconductors.

• Explanation of superconductivity in terms of Cooper pairs moving through a positive ion lattice.

• Deduction or construction of unit cell structures from crystal structure information.

• Application of the Bragg equation, nλ=2dsinθ, in metallic structures.

• Determination of the density of a pure metal from its atomic radii and crystal packing structure.

A.9 Condensation polymers

Nature of science:

• Speculation - we have had the Stone Age, Iron Age and Bronze Age. Is it possible that today’s age is the Age of Polymers, as science continues to manipulate matter for desired purposes?

Understandings:

• Condensation polymers require two functional groups on each monomer.

• NH3, HCl and H2O are possible products of condensation reactions.

• Kevlar® is a polyamide with a strong and ordered structure. The hydrogen bonds between O and N can be broken with the use of concentrated sulfuric acid.

Applications and skills:

• Distinguishing between addition and condensation polymers.

• Completion and descriptions of equations to show how condensation polymers are formed.

• Deduction of the structures of polyamides and polyesters from their respective monomers.

• Explanation of Kevlar®’s strength and its solubility in concentrated sulfuric acid.

A.10 Environmental impact - heavy metals

Nature of science:

• Risks and problems - scientific research often proceeds with perceived benefits in mind, but the risks and implications also need to be considered.

Understandings:

• Toxic doses of transition metals can disturb the normal oxidation/reduction balance in cells through various mechanisms.

• Some methods of removing heavy metals are precipitation, adsorption, and chelation.

• Polydentate ligands form more stable complexes than similar monodentate ligands due to the chelate effect, which can be explained by considering entropy changes.

Applications and skills:

• Explanation of how chelating substances can be used to remove heavy metals.

• Deduction of the number of coordinate bonds a ligand can form with a central metal ion.

• Calculations involving K sp as an application of removing metals in solution.

• Compare and contrast the Fenton and Haber-Weiss reaction mechanism.