Download - Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Section 10.5 CARBON & SILICON: NETWORK ATOMIC SOLIDS NETWORK SOLIDS: SOLIDS CONTAINING

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


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Figure 10.22

The Structures of Diamond and Graphite


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DIAMOND

• HARDEST NATURALLY OCCURING SUBSTANCE

• ELECTRICAL INSULATOR

• C ATOM COVALENTLY BONDED BY OVERLAP OF sp3 HYBRID ORBITALS


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Figure 10.22

The Structures of Diamond and Graphite


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GRAPHITE• SLIPPERY

• BLACK

• ELECTRICAL CONDUCTOR

• LAYERS OF C ATOMS STRONGLY BONDED TO 3 OTHERS THROUGH sp2 HYBRID ORBITAL

• WEAK BONDING BETWEEN LAYERS BY UNHYBRIDIZED 2p ORBITALS TO FORM DELOCALIZED BOND ELECTRICAL CONDUCTIVITY


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Figure 10.24

The p Orbitals

See also Figure 10.25.


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SILICON

• IMPORTANT CONSTITUENT OF COMPOUNDS THAT MAKE UP EARTH’S CRUST

• SILICA

FUNDAMENTAL COMPOUND

A SILICON – OXYGEN COMPOUND

EMPIRICAL FORMULA: SiO2 BUT ACTUALLY NETWORK OF SiO4 TETRAHEDRA


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Figure 10.26

The Structure of Quartz

Si at the center of tetrahedral arrangement with 4 oxygen atoms.


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SILICATES

• SIMILAR SiO4 TETRAHEDRA AS SILICA HOWEVER O/Si RATIO > 2:1

• CONTAINS SILICON-OXYGEN ANIONS

• ALSO CONTAIN CATIONS TO BALANCE NEGATIVE CHARGE

• SILICATES ARE SALTS


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Figure 10.27

Silicate Anions


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Figure 10.28

Two Dimensional Representations of (a) a Quartz Crystal and (b) a Quartz Glass

Glass is an amorphousSolid - melt silica then cool rapidly.


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Glass

• Substances are added to common glass to alter its properties.

• See Table 10.5.


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CERAMICS

• MADE FROM CLAYS (CONTAIN SILICATES)

• HARDENED BY FIRING AT HIGH TEMP.

• EXCELLENT STABILITY AT HIGH TEMP.

• RESISTANT TO CORRISION

• HOWEVER BRITTLE


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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.


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Figure 10.23

Partial Representation of the Molecular Orbital Energies in A) Diamond and B) a Typical Metal


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SEMICONDUCTORS

ELEMENTAL SILICON HAS SMALLERGAP BETWEEN FILLED AND UNFILLEDMOLECULAR ORBITALS

AT ROOM TEMP, A FEW e1- CANCROSS THE GAP PROVIDINGSEMICONDUCTIVITY

AS TEMP , MORE e1- AREEXCITED AND CONDUCTIVITY


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DOPING

CONDUCTIVITY OF SILICON ENHANCEBY DOPING Si CRYSTALS WITHOTHER ELEMENTS

TWO TYPES:

1) n-TYPE SEMICONDUCTORS

2) p-TYPE SEMICONDUCTORS


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n- TYPE SEMICONDUCTOR

REPLACE SMALL FRACTION OF SiWITH ATOMS LIKE ARSENIC (As)EACH HAVING ONE MORE Ve1- THAN Si

EXTRA e1- ‘s AVAILABLE FORCONDUCTION


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p- TYPE SEMICONDUCTOR

Si DOPED WITH ATOMS HAVING FEWER Ve1- ‘s

CREATES HOLES

ELECTRON MOVES TO FILL THE HOLE,CREATING NEW HOLE

PROCESS IS REPEATED


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Figure 10.29

Silicon Crystal Doped with (a) Arsenic and (b) Boron

N-type

P-type


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Figure 10.30

Energy Level Diagrams for (a) an n-Type Semiconductor and (b) a p-Type Semiconductor


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p-n JUNCTION

CONNECTION OF p-TYPE AND n-TYPE

MOST IMPORTANT APPLICATIONOF SEMICONDUCTORS


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Figure 10.31

The p-n Junction


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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.


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REVOLUTIONIZED ELECTRONICS!!

• p-n JUNCTION TRANSMITS CURRENT ONLY UNDER FORWARD BIAS

CONVERTS ALTERNATING CURRENT TO DIRECT CURRENT

Download - Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Section 10.5 CARBON & SILICON: NETWORK ATOMIC SOLIDS NETWORK SOLIDS: SOLIDS CONTAINING

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