An Introduction to Structures and Types of Solids

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

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 459 for the common unit cells and their lattices

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.

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

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)

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)

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 10.3 on page 463.

Gold is an example of a(n) 10 Atomic solid with metallic properties Network covalent solid Molecular solid Ionic solid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Carbon dioxide is an example of a(n) 10 Atomic solid Network covalent solid Molecular solid Ionic solid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Lithium fluoride is an example of a(n) 10 Atomic solid Network covalent solid Molecular solid Ionic solid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Krypton is an example of a(n) 10 Atomic solid Network covalent solid Molecular solid Ionic solid 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

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

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.

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.

Determining the Density of a Closest Packed Solid Complete the practice problems on page 465

Determining the Number of Ions in a Unit Cell See page 482