The structures of pure metals are crystalline (crystal lattice) with regular arrangement of metal atoms that are identical perfect spheres.

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1 HW#3 Louisiana Tech University, Chemistry 481. POGIL (Process Oriented Guided Inquiry Learning) Exercise on Chapter 3. Metals and Alloys. Why? Metals What is the structure of a metallic solid? What is a crystalline material and how it is different from an amorphous solid? What is the coordination number of a metal atom in a metallic solid? What is a unit cell? What unit cell dimensions? How different unit cell is creates different crystal systems? How a crystalline lattice is created by unit cells? What are seven crystal systems? How is metal atom packing (AAAAAAAA...,ABABABAB..., ABABABAB..., or ABCABCABC..) creates simple cubic (SC), body-centered cubic (BCC), hexagonal closest-packed (HCP), and cubic closest-packed (CCP-FCC), respectively created? How are other crystal-systems, tetragonal, orthorhombic, trigonal, monoclinic and triclinic are derived from the cubic system? What is a Bravais Lattice and how many of them are found among seven crystal systems? How do you calculate the packing efficiency of cubic (SC), body-centered cubic (BCC), and cubic closest-packed (CCP-FCC) based on simple geometric considerations? How do you calculate the number of atoms in a cubic unit cell? What is crystal dislocation? How is grain structure of metallic solids and how it is created by heating cooling? What is an alloy? What the difference between two different types of alloys, substitutional alloys and interstitial alloys? What properties are changed as an alloy is formed by a pure metal? What is an amalgam? Instructional Objectives Success Criteria Ability to answer the questions and apply concepts related to the topics given in the instructional objectives. INORGANIC CHEMISTRY By Peter Atkins, Tina Overton, Jon Rourke, Mark Weller, Fraser Armstrong, 4th Edition Prerequisites Freshman chemistry Chapter 11Structure of solids New Concepts Structure of Metals The structures of pure metals are crystalline (crystal lattice) with regular arrangement of metal atoms that are identical perfect spheres. For cubic system, they form four basic structures: simple cubic (SC), body-centered cubic (BCC), hexagonal closest-packed (HCP), and cubic closest-packed (CCP). Crystal lattice The structures of pure metals are crystalline (crystal lattice) with regular arrangement of metal atoms that are identical perfect spheres. Coordination number (CN): The number of nearest neighboring metal atoms (four, six, eight to twelve) which each atom is surrounded in the crystal lattice. Crystal Packing Unit cell: Wallpaper has regular repeating design that extends from one edge to the other. Crystals have a similar repeating unit called unit cell that extends in 3-D from one edge of the solid to the other. Unit cell has, three edges, a, b, c and there angles,.

2 Filling efficiency: Is the percent ratio of volume filled by the metals to the total unit cell volume. Cubic crystal system (a = b= c and there angles, 90. For the cubic crystals, there are four basic unit cells. Cubic Crystal Structures Open-packed A on top of A B in spaces of A layers Close-packed Between the spaces of layer below Stacking Pattern Structure (Unit cell) Coordination Number Filling efficiency AAAAAAAA... simple cubic (SC) 6 52% ABABABAB... body-centered cubic (BCC) 8 68% ABABABAB... hexagonal closest-packed (HCP) 12 74% ABCABCABC.. cubic closest-packed (CCP-FCC) 12 Bravais Lattice: A Bravais Lattice is a three dimensional lattice. A Bravis Lattice tiles space without any gaps or holes. There are 14 ways in which seven crystal systems this can be accomplished. Basic types of Bravais unit cells P (primitive),i (body centered, F(face centered), C (centered on c axis) and R/P (rombohedral/primitive) Seven Crystal Systems Crystal Unit cell Constraints Fourteen Bravis Lattices Systems 1. Cubic a = b c, 90 P,I,F (3) 2. Tetragonal a =b c, 90 P, I (2) 3. Orthorhombic a b c, 90 P, C, I, F (4) 4. Trigonal a = b c, 90 R/P (1) 5. Monoclinic a b c, 90 P, C (2) 6. Hexagonal a = b c, 90, 120 P (1) 7. Triclinic a b c, 90 P (1) Number of Atoms in the Cubic Unit Cell SC = 1 (8 corners) FCC = 4 ( 8 corners, 6 faces) BCC = 2 (8 corners, 1 body) Other unit cells? Crystal Dislocations All atoms in a piece of metal are not arranged in a regular way. Any piece of metal is made up of a large number of "crystal grains", which are regions of perfect regularity. At the grain boundaries atoms have become misaligned. Heat treatment of metals: Heating a metal tends to bring atoms into a more regular arrangement and larger grain boundaries making the metal softer. Hammering the metal when it is cold tends to produce lots of small grains harder metal. Alloys: Metallic compound composed of more than one element which can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation. Stainless steel which is an alloy of iron, nickel, and chromium. Gold jewelry which usually contains an alloy of gold and nickel Substitutional alloys: A metal atom replaces another similarly sized atom in the crystal structure. 74%

3 Interstitial alloys: Have the smaller guest metal atoms occupying holes in the close-packed structure of the host metal structure. Intermetallic compounds: Have a specific structure and therefore a constant composition. Amalgam: An alloy of mercury with another metal. Amalgam Dental: Contains mercury, silver, tin, copper, and a trace amount of zinc.

4 HW# 3 CHEM 481 Chapter 3. Metallic Structure Name: Key Questions (relatively simple to answer using the Focus Information) 1. What are the differences in the structures of following solids? a) Na(s): b) CO 2 (s)-dry ice: c) C(s)-diamond: d) CaCO 3 (s)-calcite 2. What is a crystalline material? How is C(s)-diamond different from C(s)-amorphous? 3. What is the coordination number of a metal atom in a closed packed solid? 4. Draw a simple cubic (SC) unit cell and label its axes and angles? 5. Draw a crystalline lattice with three simple cubic unit cells in all three directions, a, b, c. 6. What general unit cell dimensions for: a) Orthorhombic: a b c b) Rombohedral: a b c c) Monoclinic: a b c 7. How is simple a cubic unit cell is modified to create following crystal system? a) Triclinic: b) Rombohedral: 8. What are seven crystal systems? a) b) c) d) h) e) f) g)

5 9. Draw pictures of AAAAA.. lose packing to show how a simple cubic (SC) unit cells are created. 10. Draw pictures of ABABABAB.. lose packing to show how a body centered cubic (BCC) unit cells are created. 11. Draw pictures of ABABABAB.. close packing to show how a hexagonal closestpacked (HCP) unit cells are created. 12. On the model provided for close packed ABCABCABC.., identify the cubic closestpacked (CCP-FCC) unit cell. 13. Draw the 5 main types of Bravais Lattices and how they are distributed among crystal systems: Bravais Lattices Crystal systems: a) P b) I c) F d) C e) R/P Total Bravis Unit Cells: 14. How do you calculate the packing efficiency (52%) of cubic (SC)? 15. Calculate the number of atoms in a cubic unit cell: a) Simple cubic (SC): b) Body-centered cubic (BCC) c) Cubic closest-packed (CCP-FCC) 16. Draw a structure of a metal to show crystal dislocation?

6 17. How is grain structure of metallic solids affected by heating, tamper and cooling? 18. Describe following alloys: a) Stainless steel: b) Jewelry gold: c) Dental amalgams 19. What properties are changed as an alloy is formed from a pure metal? 20. What is an amalgam?

Chapter 3: Atomic and Ionic Arrangements. Chapter 3: Atomic and Ionic Arrangements Cengage Learning Engineering. All Rights Reserved.

Chapter 3: Atomic and Ionic Arrangements 3-1 Learning Objectives 1. 2. 3. 4. 5. 6. 7. 8. Short-range order versus long-range order Amorphous materials Lattice, basis, unit cells, and crystal structures