Friday

Law of Diffusion

Low Rate of Diffusion

• The rate of diffusion is millions of times slower in solids than in liquids

Crystalline Solids

• Crystalline solids exist either as single crystals of as groups of crystals fused together
• The total three-dimensional arrangement of particles in the crystal can be represented by a coordinate system called the lattice
• The smallest portion of a crystal lattice that shows the 3-D pattern of the entire lattice is called unit cell

Unit Cell Types

• simple cubic (4 atoms)
• body-centered (5 atoms)
• face-centered (14 atoms)

Crystalline Solids

• A crystal and its unit cells can have anyone of seven types of symmetry

Binding Forces in Crystals

• Crystal structures can also be described in terms of the types of particles in them and the types of chemical bonding between the particles

1. Ionic Crystals - The ionic crystals structure consists of positive and negative ions arranged in a regular pattern

• These crystals are hard and brittle, have high melting points, and are good insulators

2. Covalent network crystals - In covalent network crystals, each atom is covalently bonded its nearest neighboring atoms

• The covalent bonding extends throughout a network that includes a very large number of atoms
• The network solids are very hard and brittle, have high melting points, and are usually nonconductors or semiconductors

3. Metallic Crystals - The metallic crystal structure consists of metal cations surrounded by a sea of delocalized valence electrons

• The electron come from the metal atoms and belong to crystal as whole
• The freedom of these delocalized electron to more throughout the crystal explains the high electric conductivity of metal's