ssp_5y - 1 Continued 1.4 Hydrogen bonds Only between...

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1 Continued
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1-24 1.4 Hydrogen bonds Only between strongly electronegative partners (F, O, N) with covalent bonds to H e.g., H 2 O Only coordination number 2, otherwise overlap of filled orbitals because of the small size of hydrogen Weak binding: typ. 0.1 eV, but much stronger than van der Waals binding! Examples - Water (maximum density at 4 °C * ) - Biological systems (e.g., DNA) * Melting of the open ice crystal allows closer packing. Above 4 °C thermal expansion leads to an increase in density. Fig. 1.12. Hydrogen bonding between two water molecules and in ice. In an extreme ionic model the hydrogen loses its electron to one of the oxygen atoms.
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1-25 1.5 Metallic binding Fig. 1-13. The concept of metallic binding: Positive ion cores are surrounded by clouds of the electron gas. Paradigm: alkali metals Binding energy typical 1eV Undirected bonding ⇒• close packed structures (fcc, hcp) high ductility (quasi-) free electrons high el. and thermal conductivity high reflectivity Transition metals: covalent bonds (directed!) between partially filled d -orbitals W: binding energy = 8.3 eV!
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This note was uploaded on 01/19/2010 for the course MATERIALS M504 taught by Professor Adelung during the Spring '02 term at Uni Kiel.

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ssp_5y - 1 Continued 1.4 Hydrogen bonds Only between...

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