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Chapter 4

Chapter 4. Metallic Bonding. Metallic Bonding. Free movement of electrons throughout the metal structure electrical and thermal conductivity reflectivity Lack of directional bonding malleability and ductility MO theory best explains these properties. Molecules of Metal Atoms.

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Chapter 4

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  1. Chapter 4 Metallic Bonding

  2. Metallic Bonding • Free movement of electrons throughout the metal structure • electrical and thermal conductivity • reflectivity • Lack of directional bonding • malleability and ductility • MO theory best explains these properties

  3. Molecules of Metal Atoms

  4. Band Structure

  5. Metals, Insulators, and Semiconductors

  6. Doped Semiconductors

  7. Structure of Metals • crystal lattice • arrangement of metals atoms • 4 main types of arrangements • simple cubic • body-centered cubic • hexagonal close-packed • cubic close-packed

  8. Simple Cubic (sc) • coordination number of 6 • not very common • polonium

  9. Body-Centered Cubic (bcc) • coordination number of 8

  10. Close Packing • Most efficient way of filling space • Built up from hexagonal arrays of atoms vs.

  11. Hexagonal Close-Packed (hcp) • coordination number of 12 • abab arrangement

  12. Cubic-Close Packed (ccp) or Face-Centered Cubic (fcc) • coordination number of 12 • abcabc arrangement

  13. Packing Efficiency • Most metals adopt one of the more compact arrangements • As the number of valence electrons increases, arrangements generally move from bcc to hcp then to fcc

  14. Common Arrangements

  15. Unit Cells • Simplest arrangement of atoms which will reproduce the crystal structure • Can calculate how many atoms are present in each unit cell • Each atom at the corner is 1/8 inside the cell • Each atom at the face is 1/2 inside the cell • Each atom on the edge is 1/4 inside the cell • Knowing the arrangement and the density allows calculation of the metallic radius

  16. SC Unit Cell • 8(1/8) = 1 total atom per unit cell

  17. BCC Unit Cell • 1 + 8(1/8) = 2 atoms per unit cell

  18. FCC Unit Cell • 6(1/2) + 8(1/8) = four atoms per unit cell

  19. Alloys • Combination of two or more metals • held together by metallic bonds • Two types • solid solutions • alloy compounds

  20. Solid Solution Alloys • Molten metals blend to form a homogeneous mixture • atoms have to be about the same size • crystals have to be of the same arrangement • metals must have similar properties

  21. Alloy Compounds • Formation of precise stoichiometric phases • CuZn, Cu5Zn8, and CuZn3

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