CHE 132 – Exam 3

Metallic Bonds

  • Dense packing
  • over lap of large number valence orbitals
  • large interaction = strong
  • limited sharing fo e- between any two atoms, weak bonds between individual atoms

n – type semiconductor

  • excess electrons contributed by electro rich dopant atoms
  • If two atoms have more than +8 valence elecrtrons combined.

p-type semiconductor

  • holes due to elecron deficient dopant atoms
  • The sum of the valence electrons are less than 8.

What is doping, and criteria?

  • replace atoms with element of similar atomic radius and with a different # of valence electrons.

Define Crystalline Solid and Crystalline Lattice

  • Crystalline Lattice: Ordered three dimensional array of particles in a crystalline solid
  • Crystalline Solid: Substance exhibiting an ordered array of atoms, ions or molecules

Define Alloy vs Ore

  • Alloy: Metallic material that blends atoms of host metal with atoms of one or more other elements to change its properties of the host metal. 2nd element doesn’t have to be a metal.
  • Ore: naturally occuring compounds or mixtures of compounds from which elements can be extracted

Substitutional Alloy

  • atoms of added elements replace host metal in crystal lattics
  • Forms between metals of similar radii (15%)
  • i.e Bronze, Pewter, Ferrous Alloys (stainless steel)

Covalent Network Solids

  • Rigid, multidimensional array of covalently bonded atoms

Molecular Solids

  • Neutral, covalently bonded molecules held together by intermolecular attractive forces


  • Ordered collections of atoms that are larger than typical molecular solids, smaller than network covalent solids.


  • Different molecular structures of an element
  • i.e allotrope of carbon, diamond vs graphite

Graphite vs Diamond

  • Graphite: 2 dimensional covalent network of sp2 hybridized carbon atoms in sheets of fused 6 membered rings
  • soft, lubricant, sheets held together by dispersion forces
  • Diamond: network covalent solid, all carbons in sp3 hybridized tetrahedral config. (hard, non-conductive)

3 dimensional network of sp2 hybridized carbon atoms fuzed in 5 and 6 membered rings. like a soccer ball.

Allotropes of Phosphorus

White, Red

  • White Phosphorus: Molecular solid pased on P4 tetrahedra.
  • Red Phosphorus: polymer of covalently linked P4 tetrahedra , stable in air, network soild

Allotrope: Boron


forms B12 cluster arranged in icosahedral
Allrtope: Sulfur

  • more allotropes than any other element
  • most common in S8 ring

Other Ionic Crystals: Sphalerite

  • fcc unit cell of Sn2- with Zn2+ in four of the 8 tetrahedral holes

Polymorphs vs Amorphous Solids

  • Polymorphs: Same empirical formula but different crystal structure/properties
  • Amorphous Solids: non-crystalline, disordered array of atoms ions or particules in a solid state (e.g glass)

Polymorphs of Silica

  • Quartz: hexagonal ordering of SiO2 tetrahedra (Network solid)
  • Obsidian: amorphous/glassy polymorph of Silica. 

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