A.8 X-ray diffraction
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Understandings:
X-ray diffraction can be used to analyse structures of metallic and ionic compounds. Applications and skills: Application of the Bragg equation in metallic structures. Guidance: Operating principles of X-ray crystallography are not required. |
A.8 Superconductors
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Understandings:
Superconductors are materials that offer no resistance to electric currents below a critical temperature. Type 1 superconductors have sharp transitions to superconductivity whereas Type 2 superconductors have more gradual transitions. Applications and skills: Analysis of resistance versus temperature data for Type 1 and Type 2 superconductors. |
A.8 The Bardeen–Cooper–Schrieffer (BCS) theory
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Understandings:
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. Applications and skills: Explanation of superconductivity in terms of Cooper pairs moving through a positive ion lattice. |
A.9 Condensation polymers
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Understandings:
Condensation polymers require two functional groups on each monomer. NH3, HCl and H2O are possible products of condensation reactions. 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. |
A.9 Kevlar
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Understandings:
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: Explanation of Kevlar®’s strength and its solubility in concentrated sulfuric acid. |