I. Metallic Bonds

A. Properties of Metals Extremely high boiling point Shiny Malleable Ductile Good conductors of electricity

B. Metallic Bonds The bonding in metals is explained by the electron sea model Electron sea model - atoms in a metallic solid contribute their valence electrons to form a “sea” of electrons that surrounds metallic cations These delocalized electrons are not held by any specific atom and can move easily throughout the solid. Metallic bonds consist of the attractions between the free floating electrons and the positively charged metal ions

- Al3+ - - - - - - - - - - - - -

B. Metallic Bonds Cont. a force can change the shape of the metal Ions and free floating electrons rearrange their structure when a force is applied.

B. Metallic Bonds Cont. Metals are malleable (can be pounded into another shape). Conversely, a force can shatter an ionic crystal. A metal rod can be forced through a narrow opening in a die to produce wire. a) As this occurs, the metal changes shape but remains in one piece. b) If an ionic crystal were forced through the die, it would shatter. Interpreting Diagrams What causes the ionic crystal to break apart?

B. Metallic Bonds Cont. Metals can conduct an electric current

C. Metal Alloys Alloys – mixture of two or more elements, at least one of which is a metal Important because their properties are superior to those of individual elements. Generally, alloys are stronger and harder than their main metals, less malleable (harder to work) and less ductile (harder to pull into wires). Two basic types of alloys: substitutional and interstitial

C. Metal Alloys Cont. Substitutional Alloy – one in which atoms of the original metal are replaced by other atoms of similar size Examples: sterling silver, pewter, bronze, brass Interstitial Alloy - one in which the small holes in a metallic crystal are filled by smaller atoms Example: Carbon steel

C. Metal Alloys Cont. Important Alloys Steel (iron and carbon) Pewter (tin, silver, antimony, bismuth) Bronze (copper and tin) Sterling Silver (silver and copper)

Napoleon’s Buttons December 1812, Napoleon + his army return from Moscow His army was defeated by harsh Russian winter conditions. Chemist’s theory of Napoleon’s defeat At the time, all button fasteners were composed of tin (“from the greatcoats of Napoleon’s officers to the trousers and jackets of his foot soldiers.”) At cold temperatures (-30oC or -22oF) tin changes from shiny metallic to crumbly, nonmetallic powder All buttons most likely disintegrated in the cold Russian winter