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Bonding in Solids

Bonding in Solids. Sovay, Jen and Miranda. Overview. Physical properties of crystaline solids, such as melting point and hardness depend on the arrangements of particles and on the attractive forces between them. Molecular Solids.

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Bonding in Solids

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  1. Bonding in Solids Sovay, Jen and Miranda

  2. Overview • Physical properties of crystaline solids, such as melting point and hardness depend on the arrangements of particles and on the attractive forces between them

  3. Molecular Solids • Molecular solids consist of atoms or molecules held together by intermolecular forces • Intermolecular forces • Dipole: dipole forces, london dispersion forces, and hydrogen bonds • Because forces are weak, Molecular solids are soft

  4. Properties of Molecular Forces • Depend on strengths of the forces that exist between molecules • (Intermolecular forces that depend on close contact are not as effective, the melting pt is lower)

  5. Covalent-Network Solids • -Consist of atoms held together by covalent bonds • -stronger than intermolecular forces • -these solids have higher melting points and are harder than molecular forces

  6. Ionic Solids • -Ions held together by ionic bonds • -Strength depends on charges of ions • -Structure can be classified as few basic types

  7. Basic Types of Ionic Structures • NaCl, HF, KCl, AgCl, and CaO • For Na : each cation is surrounded by it’s six neighboring anions because the Na ions have a coordination number of 6 • CsCl - Each Cs ion is surrounded by eight CL, Coordination # is 8 for CS • Difference in coordination number is accounted for by the larger size of Cs • ZnS – Each of the small Zinc ions are tetrahedrally surrounded by four S ions (face centered cubic) • CaF2, BaCl2, PbF2 – (face centered cubic) all have twice as many anions as cations

  8. Metallic Solids • -Consist entirely of metal atoms • -Has several structures • - Bonding too strong to be due to London Dispersion • Not enough valence e- to be due to ordinary covalent bonds

  9. Metallic Solids (continued) • Bonding is due to valence electrons that are delocalized throughout the entire solid • Vary greatly in bonding strength • Mobility of electrons

  10. Molecular Solids Bonding Energy • Dispersion – 1.0 KJ/mole • Hydrogen Bond – 12-16 KJ/mole • Ionic – 50-100 KJ/mole • Covalent – 100-1000 KJ/mole http://www.mikeblabber.org/oldwine/chm1045/notes/forces/Bonding

  11. http://csma31.csm.jmu.edu/chemistry/augustine/gsci101/Topics/Bonding_In_Solids/primary_bonding_summary.pdfhttp://csma31.csm.jmu.edu/chemistry/augustine/gsci101/Topics/Bonding_In_Solids/primary_bonding_summary.pdf Bonding in Solids Cheat Sheet

  12. Bond Type Triangle Shows classification of bonding types based on average electronegativity differences http://chemed.chem.purdue.edu/genchem/topicreview/bp/materials/material1.html

  13. Create your own CsCl Model • CsCl is an ionic crystal with a coordination number of six. The red and yellow gummy bears are the Cl- and the Blue Gummy bear is the Cs+

  14. Questions • What kinds of attractive forces exist between particles in a) molecular crystals; b) covalent network crystals; c) ionic crystals; d) metallic crystals • A) hydrogen bonding, dipole dipole forces, London dispersion forces • B) covalent chemical bonds • C) Ionic bonds • D) Metallic Bonds

  15. Questions • Covalent bonding occurs in both molecular and covalent network solids. Why do these two kinds of solids differ so greatly in their hardness and melting points? • In molecular solids, relatively weak intermolecular forces bind the molecules in the lattice, so it requires little energy to disrupt these forces. • In covalent network solids, covalent bonds join atoms into an extended network. Melting or deforming a covalent network solid requires breaking these bonds, which requires a large amount of Energy

  16. Questions • A white substance melts with some decomposition at 730 degrees Celsius. As a solid, it is a nonconductor of electricity, but it dissolves into water to form a conducting solution. Which type of solid might this be? • Must be ionic because of relatively high melting point and properties as a conducting solution

  17. Questions • Which will have a higher melting point and why? A) B, BF3; B) Na, NaCl; C) TiO2, Ti Cl4 • A) B, covalent network lattice like C(s), versus weak dispersion forces in BF3 • B) NaCl, ionic vs metallic bonding • C) TiO2, higher charge on the O2

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