S OLIDS 10.3

S OLIDS How do the particles in a solid behave? Shape and Volume Definite Definite Melting Point Melting – the physical change of a solid to a liquid by the addition of energy as heat Melting point – the temp where solid becomes a liquid

S OLIDS Crystals – particles are arranged in an orderly, geometric, repeating pattern Crystalline solids – consists of crystals – Most Common Amorphous solid – particles arranged randomly Glass and plastics

P ROPERTIES Amorphous substances have no definite melting pt Supercooled liquids – (aka amorphous substances) substances that retain certain liquid properties even at temps at which they appear to be solid

P ROPERTIES High Density Low Compressibility Some seem compressible (wood and cork) but are not due to air pockets in the solid Low rate of diffusion

C RYSTALLINE S OLIDS Crystal structure – the 3D arrangement of particles in a crystal Unit Cell – the smallest repeating pattern of a crystal lattice 7 different types of symmetry Pattern repeats in crystal

B INDING F ORCES IN C RYSTALS Classify crystals in 4 main types 1. Ionic Crystals = + and – ions in a regular pattern Very strong forces Hard, brittle, high m.p., good insulators – Ex: Salt

B INDING F ORCES IN C RYSTALS 2. Covalent Network Crystals = each atom is covalently bonded to all neighbors Hard, brittle, high m.p, and usually semiconductors or nonconductors Ex: diamonds

B INDING F ORCES IN C RYSTALS 3. Metallic Crystals = metal cations surrounded by valence e-’s Conductors of electricity Ex: Fe

B INDING F ORCES IN C RYSTALS 4.Covalent molecular crystals = nonpolar molecules held together by London dispersion forces Low m.p., easily vaporized, soft and good insulators – Ex:CO 2