Understanding Solids: Structures & Types

1. Solids An Introduction to Structures and Types of Solids

2. Types of Solids • The broadest categories of solids are: - Crystalline solids-those with a highly regular arrangement of their components. -Amorphous solids-those with considerable disorder in their structures

3. Components of Crystalline Solids • Lattice-a three-dimensional system of points designating the positions of the atoms, ions, or molecules • Unit cell-the smallest repeating unit of the lattice • See page 432 for the common unit cells and their lattices

4. Bragg Equation • Used to determine the spacing between layers of atoms in a crystal. • nλ = 2d sin θ • n is an integer, d is the distance between atoms, θ is the angle of incidence and reflection.

5. Example Problem Using the Bragg Equation • Example problem: X-rays of wavelength 1.54 angstrom were used to analyze an aluminum crystal. A reflection was produced at θ = 19.3o. Assuming n=1, calculate the distance between the planes of atoms producing this reflection. • Answer: 233 pm

6. Types of Crystalline Solids • Ionic Solids-ions are at the points of the lattice. Ex: Sodium chloride, NaCl • Molecular Solids-covalently bonded molecules at the points of the lattice Ex: Ice, H2O molecules are at each point • Atomic Solids-atoms are at the points of the lattice. Ex: graphite (carbon at the lattice points)

7. Types of Atomic Solids • Metallic Solids- a special type of delocalized nondirectional covalent bonding occurs (this results in metals acting as good conductors of electricity) • Network Solids- nonmetallic atoms bond to each other with strong directional covalent bonds that lead to giant molecules, or networks, of atoms (example: carbon and silicon)

8. Types of Atomic Solids (continued) • Group 8A Solids-the noble gases are attracted to each other with London dispersion forces. • For a summary, see the Table 10.7 on page 458.

9. Gold is an example of a(n) 10 • Atomic solid with metallic properties • Network covalent solid • Molecular solid • Ionic solid

10. Carbon dioxide is an example of a(n) 10 • Atomic solid • Network covalent solid • Molecular solid • Ionic solid

11. Lithium fluoride is an example of a(n) 10 • Atomic solid • Network covalent solid • Molecular solid • Ionic solild

12. Krypton is an example of a(n) 10 • Atomic solid • Network covalent solid • Molecular solid • Ionic solid

13. Structure and Bonding in Metals • Metals are characterized by high thermal and electrical conductivity, malleability, and ductility. • These properties are traced to the nondirectional covalent bonding found in metallic crystals

14. Types of Metallic Crystals • Hexagonal Closest Packing-the spherical metal atoms are packed in layers in which each sphere is surrounded by 6 others. • In the second layer, the spheres do not lie directly over those in the first layer. • Instead, each occupies an indentation formed by three spheres in the first layer. • This arrangement is commonly referred to as an ABA arrangement. • Examples of metals that form hexagonal closest packing are Mg and Zn.

15. Types of Metallic Crystals (continued) • Cubic Closest Packing- the first two layers are the same as the hexagonal closest packing. • In the fourth layer, the spheres occupy the same vertical position (instead of the third) • This arrangement is commonly referred to as the ABC arrangement. • In the ABC arrangement, the unit cell is face centered. • Examples of metals that form cubic closest packing are Al, Fe, Cu, Co, and Ni.

16. Determining the Density of a Closest Packed Solid • Complete the practice problems on page 439

17. Determining the Number of Ions in a Unit Cell • See page 457