MSE- Lecture 11

MSE- Lecture 11 - SUMMARY FROM LAST CLASS Van der Waals...

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Dr. P. Lucas U of A MSE 110 Van der Waals Bonding SUMMARY FROM LAST CLASS Primary bonding: Ionic, covalent, metallic : 100-1000kJ/mole. Secondary bonding: or van der Waals bonding : 0.1-10 kJ/mole. Van der Waals bonds are weak electrostatic forces involving dipole that binds molecules. They generate a wide range of molecular solids . The dipole strength is quantified by the dipole moments μ=L× ∆δ . Due to weak van der Waals bonds, molecular solids are typically soft and have low melting points. There are four types of van der Waals bonding: Dipole-dipole : interaction between molecules with permanent dipoles. Dipole-induced dipole : interaction between a dipolar molecule and a dipole induced into a non-polar molecule. London forces : interaction of synchronized dipole fluctuation between non-polar molecules. Hydrogen bonds : interaction between acidic H and electronegative atoms O, N, F and S on neighboring molecules. H bonds have energy 10 kJ/mole while the three other 1 kJ/mole. Ice is a fairly hard solid due to a 3-D network of H bonds.
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Dr. P. Lucas U of A MSE 110 Band structure: BAND STRUCTURE AND CONDUCTIVITY IN SOLIDS The band structure describes the energy bands of a solids material. The structure of the energy bands determine the properties of electrical conductivity of a solids material. The band structure is defined by the type of bonding in the solid. There are three types of band structures. Conductors have one partially filled band. Insulator have two bands separated by a large bandgap that electrons can not cross. Semiconductors have two bands separated by a small bandgap that some electrons can cross.
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Dr. P. Lucas U of A MSE 110 Band structure: metallic conductors BAND STRUCTURE AND CONDUCTIVITY IN SOLIDS Due to the delocalized nature of valence electrons in the metallic bond, all metals are conductors. This implies that all metals must have a partially filled energy band.
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MSE- Lecture 11 - SUMMARY FROM LAST CLASS Van der Waals...

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