1. Bonding in Metals Notes 5-4 Key Ideas: 1. How do the properties of metals and alloys compare? 2. How do metal atoms combine? 3. How does metallic bonding result in useful properties of metals?

2. Metals and Alloys An alloy is a mixture made of two or more elements, at least one of which is a metal. They are generally stronger and less reactive than the pure metals from which they are made. Physical Properties Pure gold= shiny and soft Gold alloys = still shiny but much harder (mixed with copper or silver) Chemical Properties Pure iron = rusts when exposed to air and water Iron alloy = stronger, resists rust (mixed with one or more other elements to make steel) Are hard, brittle crystals a characteristic that results from a metallic bond? No!!!

3. Metallic Bonding and Metallic Properties Bonds:  Metal atoms combine in regular patterns in which the valence electrons are free to move from atom to atom (think of metal atoms floating in a sea of electrons).  Each metal ion is held in place by a metallic bond - an attraction between a positive metal ion and the many electrons surrounding it. (The more valence electrons, the stronger the bond.) 5 Properties: Malleability = easily rolled into sheets or made into complex shapes Ductility = easily bent or pulled into wires Luster = shiny and reflective Electrical Conductivity = conduct electricity easily (because electrons move freely) Thermal Conductivity = conduct heat easily (because electrons move freely)