Chapter 18 - The Solid State

18.4 Metallic Bonds and Conduction Bands

Malleability: the ability to be shaped

Ductility: the ability to be drawn out

• possible because bonds between metallic atoms are weak

Band Theory: extension of molecular orbital theory that applies to solids; describes states of electrons and that the behavior of an electron in a solid (and hence its energy) is related to the behavior of all other particles around it

• Valence Band: band of orbitals that are filled or partially filled by valence electrons
  • proximity between the energies of lower and upper portions of valence band allows for electron flow within the solid
• Conduction Band: an unoccupied band with higher energy than the valence band in which electrons can migrate

Conductor: mobile valence electrons, any material with a partially filled valence bond or a filled valence bond that overlaps with an empty conduction band

18.5 Semiconductors

metalloids: physical properties of metals and chemical properties of nonmetals

• conduction and valence bands do not overlap and are separated by an energy gap

Semiconductor: a material with electrical conductivity between metals and insulators that can be chemically modified to increase conductivity

• doping is the replacement of a metalloid with an atom with similar atomic radius but different number of valence electrons; form of substitutional alloy
  • donor level: narrow band that creates an energy difference that allows for donor electrons to reach conduction band, increasing conductivity
  • N-type conductor: dopant donates negative charges to the structure of the host element
  • accepter level: electrons leave valence band into acceptor level, creating positive holes that enhance conductivity
  • P-type semiconductor: electron poor dopant

Insulator: large gap between conductive and valence bands

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