Themes of the Day:

• Chemical Bonding (continued)
• Size of Atoms and Ions
• Structure Controls in Metallic Bonding
• Structure Controls in Covalent Bonding

Chemical Bonding

• Bonding is what happens when ions share electrons.
• Valence Related Bonding
  • Ionic bonds - electron(s) substantially transferred - e.g., Halite (NaCl) - tend to be brittle bonds
    • Balance of Forces
  • Covalent bonds - electron(s) more evenly shared - e.g., Diamond (C) - strong bonds (diamond is strongest)
    • sp hybrid orbitals in diamond
    • sp hybrid orbitals in graphite
    • more sp hybrid orbitals
  • Metallic bonds - transition metal nuclei swimming in a sea of shared electrons - e.g., Gold (Au) - malleable
    • valence and conduction bands
  • Range of Bond Character
  • Percent Ionic Character
• Bonds Not Involving Valence Electrons - generally weak (often feels greasy)
  • Hydrogen bonds - e.g., ice (H₂O) - Mohs Hardness = 3
    • Ice
  • van der Waals bonds - e.g., graphite (C) or talc (Mg₃AlSi₃O₁₀(OH)₂)
    • van der Waals bonds in graphite
• Silicate minerals, containing covalently bonded SiO₄ tetrahedra are most common in Earth's crust and mantle

Size of Atoms and Ions

• Effective Radius - also see Appendix A
• Measuring Bond Length
• Effective inoic radii as a function of charge
• Effective inoic radii as a function of coordination
• Spin state

Structure Controls in Metallic Bonding

• Closest Packing of Spheres
  • Hexagonal Closest Packing - ABAB repeat
  • Cubic Closest Packing - ABCABC repeat
• Body Centered Close Packing

Structure Controls in Covalent Bonding

• Diamond Structure - more open, not close packing