Prentice Hall © 2003 Chapter 11

Types of Solids

• Molecular Solids ex. CO2, H2O, Ar• Covalent-Network Solids ex. Diamond,

quartz, SiO2

• Metallic Solids ex. Au, Ag• Ionic Solids ex. LiF, KCl, AgCl,

CaO

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MODEL

• Close Packing of Spheres

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Close Packing of Spheres

• Describes many of the types of solids

• Assumes molecules/atoms/ions are spheres

• Characterized by– lattice– unit cell– lattice points

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Unit Cells

Prentice Hall © 2003 Chapter 11

Types of Units Cells• Simple Cubic = 8 corners occupied by 1/8 of an atom Total #

atoms in simple cubic = 1 atom

• Body-Centered = 8 corners occupied by 1/8 of an atom + 1 whole atom in center Total # atoms in simple cubic = 2 atoms

• Face-Centered = 8 corners occupied by 1/8 of an atom + 6 half- atoms on the 6 faces of the cube Total # atoms in simple cubic = 4 atoms

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The Crystal Structure of Sodium Chloride

Structures of Solids

Prentice Hall © 2003 Chapter 11

Unit Cells

Structures of Solids

Prentice Hall © 2003 Chapter 11

Most Common Types of Unit Cells based on Close Packing

of Spheres Model • Simple Cubic– 1 atom

• Body Centered Cubic (BCC)– 2 atoms

• Face Centered Cubic (FCC)– 4 atoms

1 2 4

Number of Atoms in a Cubic Unit Cell

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• Unit Cells can be used to determine the DENSITY and the SIZE of atoms

Prentice Hall © 2003 Chapter 11

Sample Problem

• The simple cubic unit cell of a particular crystalline form of barium is 2.8664 oA on each side. Calculate the density of this form of barium in gm/cm3.

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Steps to Solving the Problem

• (1.) Determine the # of atoms in the unit cell.• (2.) Convert oA (if given) to cm. (3.) Find volume

of cube using Vcube = s3 = cm3

• (4.) Convert a.m.u. to grams. [Note: 1 gm= 6.02 x 1023 a.m.u.]

• (5.) Plug in values to the formula: D = mass/volume

•

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Conversions

• Useful Conversions:

• 1 nm(nanometer) = 1 x 10-7 cm• 1 oA (angstrom)= 1 x 10-8 cm• 1 pm (picometer) = 1 x 10-10 cm

• 1 gram = 6.022 x 10 23 a. m. u. (atomic mass unit)

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Sample Problem• LiF has a face-centered cubic unit cell (same as NaCl). [F- ion

is on the face and corners. Li+ in between.]

• Determine:• 1. The net number of F- ions in the unit cell.• 2. The number of Li+ ions in the unit cell.• 3. The density of LiF given that the unit cell is 4.02 oA on an

edge. (oA = 1 x 10-8 cm)

Prentice Hall © 2003 Chapter 11

Sample Problem

• The body-centered unit cell of a particular crystalline form of iron is 2.8664 oA on each side. (a.) Calculate the density of this form of iron in gm/cm3. (b.)Calculate the radius of Fe.

• Note: First determine:• A. The net number of iron in the unit cell.• B. 1 oA = 1 x 10-8 cm

The body-centered cubic unit cell of a particular crystalline

form of an element is 0.28664 nm on each side. The density

of this element is 7.8753 g/cm3. Identify the element.