1. Solids

2. Kinetic Molecular Theory
Particles of a solid more closely packed than those of a liquid or gas.
Intermolecular forces are more effective.
These forces tend to hold the particles in relatively fixed positions where they vibrate.
Solids are more ordered than liquids or gases.

3. Types of Solids
Crystalline solids – consists of crystals – particles arranged in an orderly, geometric, repeating pattern
Amorphous solids – particles are arranged randomly
Plastics and glass

4. Properties of Solids Definite shape and volume Definite melting point
Crystalline solids only
Amorphous solids melt over a range of temperatures
High density and incompressibility
Low rate of diffusion

5. Crystalline Solids
Exist either as single crystals or groups of crystals fused together.
Crystal structure is the total 3-D arrangement of particles
The crystal can be represented by a coordinate system called a lattice.
Unit cell is the smallest part of a crystal lattice that shows the 3-D pattern of the entire lattice

6. Crystal Structure
The unit cell of a crystal can have one of 7 types of symmetry
Cubic
Tetragonal
Hexagonal
Trigonal
Orthorhombic
Monoclinic
Triclinic

7. cubic

8. Tetragonal

9. Hexagonal

10. Trigonal

11. Orthorhombic

12. monoclinic

13. triclinic

14. Binding Forces in Crystals
Crystalline solids can also be classified by the types of particles in them and the types of chemical bonds between the particles
There are four types of crystals in this method of classification

15. Ionic Crystals
Positive and negative ions arranged in a regular pattern
Ions can be monatomic or polyatomic
Hard and brittle, high melting points, good insulators
Examples – NaCl, MgF2

16. Covalent Network Crystals
Single atoms covalently bonded to nearest neighboring atoms
Covalent bonding extends throughout a network of large numbers of atoms
Very hard and brittle, rather high melting points, nonconductors
Examples – (SiO2)x (quartz) and Cx (diamond)

17. Metallic Crystals
Metal cations surrounded by a sea of delocalized valence electrons which are donated by the metal atoms and belong to the crystal as a whole.
High electrical conductivity, wide range of melting points
Examples – mercury, copper, lead

18. Covalent Molecular Crystals
Covalently bonded molecules held together by intermolecular forces
Covalent bonds are stronger than the intermolecular forces
Low melting points, easily vaporized, relatively soft, good insulators
Examples – H2O, NH3, CH4, H2

19. Amorphous Solids Amorphous means without shape
Atoms are not arranged in a regular pattern.
Hold shape for long time, but may flow slowly
Glass and plastics are examples