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Structures and Types of Solids

This overview explores the two primary types of solids: crystalline and amorphous. Crystalline solids feature a regular arrangement of particles and can be classified based on their unit cell types, such as simple cubic and face-centered cubic. In contrast, amorphous solids have a disordered structure, exemplified by glass. The determination of solid structures often involves X-ray diffraction, guided by the Bragg equation. Furthermore, the discussion extends to bonding models in metals and the properties of alloys, highlighting their significance in materials science.

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Structures and Types of Solids

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  1. Structures and Types of Solids

  2. Two types of solids • 1. Crystalline solids • highly regular arrangement of their particles • crystals- at microscopic level

  3. How are they crystals? • Lattice - 3-D system of points indicating position of ions, atoms or molecules that make up the substance

  4. Unit cell • Smallest repeating pattern of the lattice- extend in all directions for the structure

  5. 3 types of unit cells • A. Simple cubic • polonium metal • B. Body centered cubic • Uranium metal • C. Face centered cubic • Gold metal

  6. Two types of solids • 2. Amorphous solids- considerable disorder in their structure • EX- glass- liquid that is “frozen in place”

  7. Crystalline solids?? • How do we determine the structure of the solid? • X-ray diffraction!!

  8. Bragg equation • 1915 Noble prize in physics • n = 2dsin • where n= integer = wavelength of x-rays d= distance b/w atoms = angle of incidence

  9. Types of crystalline solids • Easy to classify based on what particle is at lattice point

  10. Types of crystalline solids • Explains why solids have different properties • melting point • conductivity • ductility

  11. Three types • 1. Ionic solids- have ions at the points of the lattice • NaCl

  12. Three types • 2. Molecular solid- have discrete covalently bonded molecules at lattice points • ice

  13. Three types • 3. Atomic solids- substances that have atoms at the lattice points • C, B, Si and all metals

  14. Three types of atomic solids • A. metallic solids- delocalized nondirectional covalent bonding

  15. Three types of atomic solids • B. network solids- atoms bond with strong directional covalent bonds that lead to giant molecules (networks)

  16. Three types of atomic solids • C. Group 8 solids- noble gas elements are attracted by London dispersion forces

  17. Structure and Bonding in Metals • Metals- high thermal and electric conductivity, malleability, ductility- due to nondirectional covalent bonding

  18. Closest packing • Spherical atoms packed together and bonded in all directions • spheres packed in layers-each surrounded by 6 others

  19. Three arrangements • Hexagonal closest packed structure (hcp)- aba arrangement • has hexagonal unit cell

  20. hcp structure • Every other layer has the same vertical position • EX: Mg, Zn

  21. Three arrangements  • Cubic closest packed structure (ccp)- abc arrangement • face-centered cubic cell

  22. ccp structure • Every 4th level occupies the same vertical position • EX: Al, Fe, Cu, Co, Ni

  23. Three arrangements • Body centered cubic unit cell (bcc)- spheres touch along the body diagonal of the cube

  24. bcc unit cell • Most spread apart arrangement • EX: alkali metals

  25. Counting atoms... • Need to know number of atoms in a unit cell

  26. Face-centered • 8 cubes share one cell • 1/8 x 8 corners + • 1/2 x 6 faces = • net 4 whole spheres

  27. Density of ccp solid • Ag crystallizes in a ccp structure. The radius of a silver atom is 144pm. Calculate the density of solid silver.

  28. Bonding models for metals • Model must account for physical properties: • A. shape can be changed fairly easily- malleable and ductile

  29. Bonding models for metals • B. durable • C. high melting points

  30. Bonding models for metals • Indicates the bonding is STRONG and NONDIRECTIONAL • or difficult to separate metals atoms, but easy to move them

  31. The model is... • Electron “sea”model • metal cations in sea of e- (mobile e- for conductivity and cations can be moved around when hammered

  32. Last topic-metal alloys! • Metals introduced into the crystal structure of other metals

  33. Alloy • A substance that contains a mixture of elements and has metallic properties

  34. Two types of alloys • Substitutional alloy- some of the host metal atoms are replaced by other metal atoms of similar size

  35. Substitutional alloys • EX: Brass (1/3 of copper atoms replaced with zinc) • Pewter (85%Sn, 7%Cu, 6%Bi, 2%At)

  36. Two types of alloys • Interstitial alloy- formed when some of the holes in a close packed metal structure are occupied by smaller atoms

  37. Interstitial alloy • EX: Steel (carbon atoms into iron) • Strengthens iron by adding strong directional bonds

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