1. Solids  Metallic Crystals  Alloys – mixtures of metals – done to strengthen or make a metal less brittle or subject to oxidation.  2 types  Substitutional – when metal atoms are of similar size  Interstitial – when one atom is smaller than the other, fills in the spaces between the larger ones Substitutional Interstitial

2. Solids  Metallic crystals  Substitutional alloy  Silver alloyed with gold, replace one set of attractive forces with an almost equal set of attractive forces with the added metal.  Result: alloy has properties that tend to fall somewhere between the two separate metals

3. Solids  Metallic crystals  Interstitial alloys  Incorporate one atom into the existing structure with little change in volume- results in increased density  Increases total attractive forces in the alloy  Usually stronger and harder than original materials

4. Solids  Ionic Crystals  Attraction of a cation and an anion is the strongest attractive force known in chemistry.  Alternating positive & negative ions  Almost all ionic compounds are solids with rigid crystal structures (lattices)  Take a large amount of lattice energy to separate the ions!