Solid State Electrical Conductivity & Reactivity Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

Solid State Electrical Conductivity Solid ionic compounds are poor electrical conductors. Mobile charges (ions or electrons) are needed for electrical conductivity. The difference in energy of bonding and antibonding orbitals in a solid can explain many electrical properties.

Bonding Band Theory Si silicon (diamond structure) directional localized bonds Si 4 Si atoms 4/17/2017

Bonding Band Theory directional localized bonds Si 4 Si atoms conduction band band gap valence band for silicon the valence band is full the conduction band is empty 4/17/2017

Smaller gap for heavier elements Band Gap carbon (diamond) silicon germanium tin Smaller gap for heavier elements 4/17/2017

Band Gap C diamond - insulator Si semimetal, semiconductor Ge Sn graphite has a different structure than diamond and is a conductor C Si Ge Sn diamond - insulator semimetal, semiconductor grey tin - metallic, conductor Smaller gap for heavier elements 4/17/2017

Bonding Covalent and Metallic Bonding directional localized bonds C 4 C atoms conduction band no band gap valence band Insulator Metallic Conductor 4/17/2017

Density of States Insulator Semiconductor Metal overlapping mo’s in extended structure conduction band valence band levels are not uniformly spaced Insulator Semiconductor Metal 4/17/2017

Conductivity e- metal semiconductor insulator T   4/17/2017

Band Gap average T2 > T1 Energy  number of electrons T2 > T1 free electrons or holes move charge higher temperature puts more e- in conduction band

Conductivity e- metal semiconductor insulator T   4/17/2017

Elements in Semiconductors B C N O F Al Si P S Cl Cu Zn Ga Ge As Se Br Ag Cd In Sn Sb Te I Intrinsic: Si, Ge, Fe3O4 Alloys: GaP, GaAs, ZnS, CdS, CdSe, SiC 4/17/2017

Doped Semiconductors n-type semiconductor 1% As in Ge p-type excess mobile electrons p-type semiconductor 1% Ga in Ge excess mobile holes conduction band valence band 4/17/2017

Diode n-type p-type a combination of an n-type semiconductor and a p-type semiconductor that allows current flow in a preferred direction 4/17/2017

Diode - + n-type p-type e- flow can occur with e- moving to more stable energy levels Both conduct because there are mobile electrons or holes and locations to move to. e- Battery provides e- on one side and drain on the other side. - e- + 4/17/2017

Diode - + n-type p-type Current flow in the reverse direction requires e- move to higher energy levels, and occurs only with large applied potentials (breakdown voltage). The semiconductors are charge neutral, and additional charge will build up in the valence band preventing significant current flow. - + e- e- 4/17/2017

Diode Current   Reverse Bias Forward Bias  Applied Voltage

Light Emitting Diodes band gap  = E h = c  wavelength (color) h = 6.62 x 10-34 J·s·molecule-1 c = 3.00 x 108 m·s-1

Solid State Photoreactions Ag+ Br- Ag+ Br- Ag+ Br- h Br- Ag+ Br- Ag+ Br- Ag+ Ag+ Br- Ag+ Br- Ag+ Br- Br- Ag+ Br- Ag+ Br- Ag+ Ag+ Br- Ag+ Br- Ag+ Br- Br- Ag+ Br- Ag+ Br- Ag+

Solid State Photoreactions Ag+ Br- Ag+ Br- Ag+ Br- Br- Ag+ Br- Ag+ Br- Ag+ Ag+ Br- Ag+ Br Ag Br- Br- Ag+ Br- Ag+ Br- Ag+ Ag+ Br- Ag+ Br- Ag+ Br- Br- Ag+ Br- Ag+ Br- Ag+

AgBr(s)  Ag(s) + ½ Br2(l) ½ Br2(g) 325 kJ·mol-1 Ag+(g) Br-(g) Ag(g) Ag(l) Ag(s) + Br2(l) 100 kJ·mol-1 AgBr(s) major energy requirement is reverse of EA of Br- 4/17/2017

AgBr(s)  Ag(s) + ½ Br2(l) E = 325,000 J·mol-1  = E h = c  h = 6.62 x 10-34 J·s·molecule-1 c = 3.00 x 108 m·s-1 mol = 6.02 x 1023 molecules causes sun darkening glasses to turn darker.  = hc E = 3.68 x 10-7 m = 3680 Å (near uv) 4/17/2017

1-2-3 Superconductor YBa2Cu3O7 barium yttrium copper oxygen

Resistivity metal superconductor resistivity resistivity temperature Tc

Superconductivity

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Heavier Members of a Family tend to form single bonds silicon dioxide quartz, glass, sand C O carbon dioxide 4/17/2017

Si silicon 4/17/2017