1. There are three main types of primary bonding: ionic, covalent, and metallic. Ionic bonding involves the transfer of electrons between atoms. Covalent bonding involves the sharing of electrons between atoms. Metallic bonding involves delocalized electrons that act as a "sea" or "glue" between positively charged metal ions. 2. In addition to primary bonds, there can also be secondary bonding interactions between molecules called van der Waals forces. These weaker interactions influence physical properties. 3. Crystal structure, bonding type, and defects all impact a material's properties. Ionic and covalent materials have large bond energies and are brittle with high melting points, while metallic materials have variable bond energies and

3. Ionic Bonding • Occurs between + and - ions. • Requires electron transfer. • Large difference in electronegativity required. • Example: NaCl Na (metal) unstable Cl (nonmetal) unstable electron + - Coulombic Attraction Na (cation) stable Cl (anion) stable

4. Examples: Ionic Bonding • Predominant bonding in Ceramics Adapted from Fig. 2.7, Callister & Rethwisch 3e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the Chemical Bond , 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University. Give up electrons Acquire electrons NaCl MgO CaF 2 CsCl

5. c02f09

9. SECONDARY BONDING • Permanent dipoles -molecule induced • Fluctuating dipoles -general case: -ex: liquid HCl -ex: polymer secondary bonding secondary bonding secondary bonding asymmetric electron clouds + - + - secondary bonding H H H H H 2 H 2 secondary bonding ex: liquid H 2 H Cl H Cl + - + - secondary bonding

10. Summary: Bonding Type Ionic Coulombic force Covalent Metallic Secondary Van der Waals Bond Energy Large Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury smallest Comments Nondirectional ( ceramics ) Directional ( semiconductors , ceramics polymer chains) Nondirectional ( metals ) Directional inter-chain ( polymer ) inter-molecular

11. Summary: Primary Bonds Ceramics (Ionic & covalent bonding): Large bond energy large T m large E small  Metals (Metallic bonding): Variable bond energy moderate T m moderate E moderate  Polymers (Covalent & Secondary): Directional Properties Secondary bonding dominates small T m small E large  secondary bonding

12. Crystal Structure

13. Crystal Structure

14. Crystal Structure

15. Crystal Structure

16. Crystal Structure

17. Crystal Structure

18. Crystal Structure

19. Crystal Structure

20. Disfigurement Crystal Structure

21. Edge Dislocation

22. Screw Dislocation

23. Screw Dislocation

24. Point Defect