SOLIDSChapter 12.2

Objectives:

1. Describe the motion of particles in solids and the properties of solids according to the kinetic-molecular theory.

2. Distinguish between the two types of solids.

3. Describe the different types of crystal symmetry. Define crystal structure and unit cell.

Properties of Solids and Kinetic-Molecular Theory

Particles are more closely packed. Intermolecular forces are much more effective in

solids. Hold molecules in fixed position, only vibration

movement More ordered than other phases

Two types of Solids Crystalline solids:

Consist of crystals, which are, a substance in which the particles are arranged in an orderly, geometric, repeating pattern.

Amorphous solid: Solids whose particles are arranged randomly

Ex: glass and plastic

Definite Shape and Volume Tightly packed particles

Very little space for compression Do not flow b/c fixed position of particles

Amorphous solids do flow (random arrangement)Definite Melting Point

Melting Physical change of a solid to a liquid by the

addition of heat. (Temperature which a solid becomes a liquid) Kinetic energy of particles overcome attractive

forces holding them together. Supercooled Liquids

Substances that retain certain liquid properties even at temperatures at which they appear to be solid.

High Density and Incompressibility

Particles are more closely packed together Why are wood and cork compressible?

They are not!! They contain pores filled with air, which is

what can be compressedLow Rate of Diffusion Can it happen?

YES, But millions of times slower than liquids and gases

Crystalline Solids Crystal Structure:

Total 3-D arrangement of particles is a crystal – lattice

Unit Cell: Smallest portion of a crystal lattice that

show the 3-D pattern of the entire lattice Seven types of symmetry

FluoriteCubic Emerald

Hexagonal

Chalcopyrite

Tetragonal

Aragonite Orthorhomb

icAzurite

Monoclinic

Rhodonite

Triclinic

CalciteTrigonal

Binding forces in Crystals Four Types

1) Ionic Crystalso Consist of positive and negative ionso Ions – monatomic or polyatomico Form when o Group 1 or 2 metals combine with group 16

or 17 nonmetalso Hard and brittleo High melting pointo Good insulators

2) Covalent network Crystalso Covalently bonded atoms making a

network with a very large number of atoms ( 3-D)

o Examples: diamond, Quartz, o diamond, Quartz, silicon carbide

o Very hard and brittleo Rather high melting pointso Usually nonconductors and

semiconductors

3) Metallic Crystalso Metal atoms surrounded by sea of

electronso Hard and malleableo High conductivityo Melting points vary (very high to

low)

4) Covalent Molecular Crystalso Covalently bonded molecules held

together by intermolecular forceso Examples: Nonpolaro Hydrogen, methane, benzeneo Weak London dispersion forces

o Examples: Polaro Water, ammoniao Hydrogen bonding, stronger dipole-

dipole forceso LOW melting pointso Easily vaporizedo Relatively softo Good insulators

Amorphous Solids Amorphous:

Comes from Greek word: “without shape”

Some amorphous solids DO FLOW Very slowly

Example: window glass thicker on the bottom

Examples: Glass, fiberglass, plastic