Solids
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.
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
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
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
Crystal Structure The unit cell of a crystal can have one of 7 types of symmetry Cubic Tetragonal Hexagonal Trigonal Orthorhombic Monoclinic Triclinic
cubic
Tetragonal
Hexagonal
Trigonal
Orthorhombic
monoclinic
triclinic
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
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
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)
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
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
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