Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Section 10.5 CARBON & SILICON: NETWORK ATOMIC SOLIDS NETWORK SOLIDS: SOLIDS CONTAINING STRONG DIRECTIONAL COVALENT BONDS TO FORM A SOLID THAT MIGHT BE BEST VIEWED AS A “GIANT MOLECULE” EXAMPLE: DIAMOND AND GRAPHITE

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Figure The Structures of Diamond and Graphite

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 DIAMOND HARDEST NATURALLY OCCURING SUBSTANCE ELECTRICAL INSULATOR C ATOM COVALENTLY BONDED BY OVERLAP OF sp 3 HYBRID ORBITALS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure The Structures of Diamond and Graphite

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 GRAPHITE SLIPPERY BLACK ELECTRICAL CONDUCTOR LAYERS OF C ATOMS STRONGLY BONDED TO 3 OTHERS THROUGH sp 2 HYBRID ORBITAL WEAK BONDING BETWEEN LAYERS BY UNHYBRIDIZED 2p ORBITALS TO FORM DELOCALIZED  BOND  ELECTRICAL CONDUCTIVITY

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure The p Orbitals See also Figure

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 SILICON IMPORTANT CONSTITUENT OF COMPOUNDS THAT MAKE UP EARTH’S CRUST SILICA FUNDAMENTAL COMPOUND A SILICON – OXYGEN COMPOUND EMPIRICAL FORMULA: SiO 2 BUT ACTUALLY NETWORK OF SiO 4 TETRAHEDRA

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Figure The Structure of Quartz Si at the center of tetrahedral arrangement with 4 oxygen atoms.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 SILICATES SIMILAR SiO 4 TETRAHEDRA AS SILICA HOWEVER O/Si RATIO > 2:1 CONTAINS SILICON-OXYGEN ANIONS ALSO CONTAIN CATIONS TO BALANCE NEGATIVE CHARGE SILICATES ARE SALTS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure Silicate Anions

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Figure Two Dimensional Representations of (a) a Quartz Crystal and (b) a Quartz Glass Glass is an amorphous Solid - melt silica then cool rapidly.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Glass Substances are added to common glass to alter its properties. See Table 10.5.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 CERAMICS MADE FROM CLAYS (CONTAIN SILICATES) HARDENED BY FIRING AT HIGH TEMP. EXCELLENT STABILITY AT HIGH TEMP. RESISTANT TO CORRISION HOWEVER BRITTLE

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Semiconductors Elemental Silicon has same structure as diamond. (Both in Group 4A) Diamond is insulator due to large energy gap between filled & unfilled Molecular Orbitals.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure Partial Representation of the Molecular Orbital Energies in A) Diamond and B) a Typical Metal

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 SEMICONDUCTORS ELEMENTAL SILICON HAS SMALLER GAP BETWEEN FILLED AND UNFILLED MOLECULAR ORBITALS AT ROOM TEMP, A FEW e 1- CAN CROSS THE GAP PROVIDING SEMICONDUCTIVITY AS TEMP , MORE e 1- ARE EXCITED AND CONDUCTIVITY 

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 DOPING CONDUCTIVITY OF SILICON ENHANCE BY DOPING Si CRYSTALS WITH OTHER ELEMENTS TWO TYPES: 1) n-TYPE SEMICONDUCTORS 2) p-TYPE SEMICONDUCTORS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 n- TYPE SEMICONDUCTOR REPLACE SMALL FRACTION OF Si WITH ATOMS LIKE ARSENIC (As) EACH HAVING ONE MORE Ve 1- THAN Si EXTRA e 1- ‘ s AVAILABLE FOR CONDUCTION

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 p- TYPE SEMICONDUCTOR Si DOPED WITH ATOMS HAVING FEWER Ve 1- ‘ s CREATES HOLES ELECTRON MOVES TO FILL THE HOLE, CREATING NEW HOLE PROCESS IS REPEATED

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Figure Silicon Crystal Doped with (a) Arsenic and (b) Boron N-type P-type

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure Energy Level Diagrams for (a) an n-Type Semiconductor and (b) a p-Type Semiconductor

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 p-n JUNCTION CONNECTION OF p-TYPE AND n-TYPE MOST IMPORTANT APPLICATION OF SEMICONDUCTORS

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Figure The p-n Junction

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 RECTIFIER DEVICE THAT PRODUCES A PULSATING DIRECT CURRENT (i.e., FLOWS IN ONLY ONE DIRECTION) FROM ALTERNATING CURRENT (i.e., FLOWS IN BOTH DIRECTIONS ALTERNATELY.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 REVOLUTIONIZED ELECTRONICS!! p-n JUNCTION TRANSMITS CURRENT ONLY UNDER FORWARD BIAS CONVERTS ALTERNATING CURRENT TO DIRECT CURRENT