Coordination # = 8 2 Particles per Unit Cell Body-Centered Cubic Sodium

Conduction band 3s band Valence band Application of a voltage to the metal (perhaps in the form of a wire) would excite electrons into the conduction band (unoccupied molecular orbitals) where they would be free to move throughout the crystal.

Coordination # = 12 4 Particles per Unit Cell Face-Centered Cubic Copper

ABC…ABC…ABC Stacking

A C B X X X X X A

Coordination # = 12 4 Particles per Unit Cell Face-Centered Cubic AKA… cubic closest packing Copper

Hexagonal Unit Cell AB…AB…AB stacking Magnesium AKA…hcp Conduction band Valence band Hexagonal Unit Cell AB…AB…AB stacking Magnesium AKA…hcp

Insulator Semiconductor ex: Si or Ge A material that doesn’t conduct electricity because the band gap is too large. A material (whose band gap is not too big) that has low conductivity at room temp., but increases in conductivity as the temperature increases.** **Opposite of metals whose conductivity goes down as the temperature increases.** Insulator Semiconductor ex: Si or Ge

silicon doped with phosphorous n-type semiconductor

silicon doped with boron p-type semiconductor

Current flows Current does not flow Rectifier – allows current to flow in just one direction Current does not flow

Alloy: a mixture of elements that has metallic properties. Brass Substitutional Alloy

Alloy: a mixture of elements that has metallic properties. Steel Interstitial Alloy