11

CHAPTER 10CHAPTER 10

ORBITAL HYBRIDIZATIONORBITAL HYBRIDIZATION andand

MOLECULAR ORBITALSMOLECULAR ORBITALS

Problems 1-15 + all bold numbered problemsProblems 1-15 + all bold numbered problems

22

33ORBITALS AND BONDING THEORIESORBITALS AND BONDING THEORIES• There are two major theories of bondingThere are two major theories of bonding• The Valence Bond (VB) TheoryThe Valence Bond (VB) Theory

–SimpleSimple–Explains geometryExplains geometry–An extension of the Atomic TheoryAn extension of the Atomic Theory–Fails to account for some paramagnetic Fails to account for some paramagnetic

propertiesproperties–Fails to explain delocalized bondsFails to explain delocalized bonds

• The Molecular Orbital (MO) TheoryThe Molecular Orbital (MO) Theory–More complexMore complex–Explains magnetic propertiesExplains magnetic properties–Explains delocalized bondsExplains delocalized bonds

44

Two Theories of BondingTwo Theories of Bonding

• VALENCE BOND THEORY — VALENCE BOND THEORY — Linus PaulingLinus Pauling

• valence electrons are localized valence electrons are localized between atoms (or are lone between atoms (or are lone pairs).pairs).

• half-filled atomic orbitals half-filled atomic orbitals overlap to form bondsoverlap to form bonds

55MinimumMinimumAttractionAttraction

Maximum Maximum AttractionAttraction Free atomFree atom

Repulsion

66

Sigma Bond Sigma Bond Formation by Formation by

Atomic Orbital Atomic Orbital OverlapOverlap

•• ••

sigma bond ( )

+HH

Two s Two s orbitals orbitals overlapoverlap

77

Sigma Bond Formation by Atomic Sigma Bond Formation by Atomic Orbital OverlapOrbital Overlap

Two s orbitals Two s orbitals overlapoverlap

Two p Two p atomic atomic orbitals orbitals overlapoverlap

s & p s & p atomic atomic orbitals orbitals overlapoverlap

H + F HF

88VALENCE BOND THEORYVALENCE BOND THEORY

• Bonds form when: atomic orbitals overlap, Bonds form when: atomic orbitals overlap, and two electrons with opposite spin are and two electrons with opposite spin are present. present.

• The resulting lower energy state is called a The resulting lower energy state is called a covalent bond.covalent bond.

• If the overlapping orbitals are 1s type If the overlapping orbitals are 1s type orbitals, the resulting bondorbitals, the resulting bond is called a sis called a s1s + 1s1s + 1s (previous H(previous H22) )

• If the overlapping orbitals are 1s and 2p type If the overlapping orbitals are 1s and 2p type orbitals, the resulting bondorbitals, the resulting bond is called a sis called a s1s + 2p1s + 2p. .

• If the overlapping orbitals are 2p type If the overlapping orbitals are 2p type orbitals, the resulting bondorbitals, the resulting bond is called a sis called a s2p + 2p2p + 2p

99

• VBT works well for explaining atomic VBT works well for explaining atomic orbital overlap between 1s-1s, 2p-2p and orbital overlap between 1s-1s, 2p-2p and 1s-2p to make new bonds1s-2p to make new bonds

• What does VBT say about more complex What does VBT say about more complex molecules with more then 2 atom systemsmolecules with more then 2 atom systems

VALENCE BOND THEORYVALENCE BOND THEORY

1010

VALENCE BOND THEORYVALENCE BOND THEORY

•VBT can not account for a 109.5º angle in CH4

due to 2p orbitals constrained 90º bond angle•AO of 90º do not correspond to 109.5º

??

1111

A new theory is neededA new theory is needed

Linus Pauling proposes Hybrid Orbital Theory

1212

Advanced Theories of Advanced Theories of Chemical BondingChemical Bonding

Atomic OrbitalsAtomic Orbitals MoleculesMolecules

1313

Hybrid OrbitalsHybrid Orbitals• Atomic orbitals in the free atoms are “Mixed” to Atomic orbitals in the free atoms are “Mixed” to

make a new Hybrid Orbital for molecules with make a new Hybrid Orbital for molecules with more then 2 atomsmore then 2 atoms

• An example of mixing an An example of mixing an ss and and pp atomic orbital to atomic orbital to make a NEW Hybrid make a NEW Hybrid spsp orbital orbital

• # AO # AO = = # of HO # of HO

+

1414

spsp22

spsp33

spsp33dd

New HO from AONew HO from AO+

s p sp2 sp2p sp2

+

s p sp3 sp3p sp3p sp3

+

s p sp 3d sp3dp sp3dp sp3d

d sp3d

1515

spsp33dd22

These new HO do two things1. Allow the orbitals to physically rearrange in such a

fashion to adopt the 109.5º bond angle in the sp3 for example

2. Account for 6 coordinate molecules as in the case of sp3d2

+

s p sp3d2 sp3d2p sp 3dp sp3d2

d sp3d2d

sp3d2

1616

Hybrid Orbitals: a “Mixing” of Hybrid Orbitals: a “Mixing” of AO’sAO’s

• Other possibilitiesOther possibilities

–one one ss with one with one pp (just (just described)described)

–one one ss with two with two pp’s’s–one one ss with three with three pp’s’s–one one ss with three with three pp’s and one ’s and one dd

–one one ss with three with three pp’s and two ’s and two dd’s’s

New NameNew Name spsp spsp22

spsp33

spsp33dd spsp33dd22

These are the newly mixed Hybrid OrbitalsThese are the newly mixed Hybrid Orbitals

1717

Hybridization of Atomic OrbitalsHybridization of Atomic OrbitalsSpSp3 3

• To form polyatomic molecules having three To form polyatomic molecules having three or more atoms, it is frequently necessary or more atoms, it is frequently necessary (always in the second period) to hybridize (always in the second period) to hybridize the atomic orbitals of the central atom to the atomic orbitals of the central atom to permit maximum orbital overlap and to permit maximum orbital overlap and to maximize the number of bonds formed. maximize the number of bonds formed.

• Carbon, for example, always forms four (4) Carbon, for example, always forms four (4) bonds. bonds.

1818

Orbitals needed to hybridize

1919

2020

Bonding in CHBonding in CH44

Need to use 4 atomic Need to use 4 atomic orbitals — s, porbitals — s, pxx, p, pyy, , and pand pzz — to form 4 — to form 4 new hybrid orbitals new hybrid orbitals pointing in the correct pointing in the correct direction.direction.

109o109o

2121

Bonding in a Tetrahedron Bonding in a Tetrahedron Formation of Hybrid Atomic Formation of Hybrid Atomic

OrbitalsOrbitals

4 C atom orbitals 4 C atom orbitals hybridize to form four hybridize to form four equivalent spequivalent sp33 hybrid hybrid atomic orbitals.atomic orbitals.

2222

spsp33

• These hybrid atomic orbitals are These hybrid atomic orbitals are linear linear combinationscombinations of the atomic orbitals. of the atomic orbitals.

• The number of hybrid orbitals produced is always The number of hybrid orbitals produced is always equal to the number of atomic orbitals hybridized.equal to the number of atomic orbitals hybridized.

2323

New Linear CombinationNew Linear Combination

2424

Bonding in a TetrahedronBonding in a TetrahedronFormation of Hybrid Atomic OrbitalsFormation of Hybrid Atomic Orbitals

4 C atom orbitals hybridize to form 4 C atom orbitals hybridize to form four equivalent spfour equivalent sp33 hybrid atomic hybrid atomic orbitals.orbitals.

2525

spsp33

• Hybridization for water and ammonia is Hybridization for water and ammonia is

explained on page 445.explained on page 445.

• Figures 10.8 & 10.9.

• (Examples 10.1 and 10.2 page 446.) (Examples 10.1 and 10.2 page 446.)

• Predict the hybridization and geometry for Predict the hybridization and geometry for

CHClCHCl33 and OF and OF22. Describe the sigma bonds . Describe the sigma bonds

in each molecule.in each molecule.

2626Figure 10.8

2727Figure 10.9

2828spsp22

• If one If one ss orbital and two orbital and two pp orbitals are orbitals are combined, the resulting combined, the resulting hybridhybrid orbitals are orbitals are called called spsp22 orbitals orbitals. .

• The trigonal planar shape of this set of The trigonal planar shape of this set of three orbitals is consistent with the VSEPR three orbitals is consistent with the VSEPR theory. theory.

• Figure 10.10, page 448, and , page 448, and Figure 10.8 (3rd ed.) illustrates this Figure 10.8 (3rd ed.) illustrates this

concept. concept.

• The orbital box diagrams can be used to The orbital box diagrams can be used to confirm the bonding. confirm the bonding.

• BHBH33 is and example (show model). is and example (show model).

2929

Figure 10.10

3030

Using VB TheoryUsing VB TheoryBonding in BFBonding in BF33

F

F F

Boron configuration

2p2s1s•• ••

••••

••

•• ••

••••

B

planar triangleplanar triangleangle = 120angle = 120oo

3131

Bonding in BFBonding in BF33

• How to account for 3 bonds 120How to account for 3 bonds 120oo apart using a spherical s apart using a spherical s orbital and p orbitals that are 90orbital and p orbitals that are 90oo apart? apart?

• Pauling said to modify VP approach with Pauling said to modify VP approach with ORBITAL ORBITAL HYBRIDIZATIONHYBRIDIZATION

• — — mix available orbitals to form a new set of mix available orbitals to form a new set of orbitals — HYBRID ORBITALS — that will give the orbitals — HYBRID ORBITALS — that will give the maximum overlap in the correct geometry.maximum overlap in the correct geometry.

3232

rearrange electronshydridize orbs.

unused porbital

three sp 2 hybrid orbitals

2p2s

Bonding in BFBonding in BF33

3333

• • The three hybrid orbitals are made The three hybrid orbitals are made from 1 s orbital and 2 p orbitals from 1 s orbital and 2 p orbitals 3 sp 3 sp22 hybrids.hybrids.• • Now we have 3, half-filled HYBRID Now we have 3, half-filled HYBRID orbitals that can be used to form B- F orbitals that can be used to form B- F sigma bonds. sigma bonds.

Bonding in BFBonding in BF33

rearrange electronshydridize orbs.

unused porbital

three sp2 hybrid orbitals

2 p2 s

120o

threesp2 hybridorbitals•

3434

Bonding in BFBonding in BF33

An orbital from each F overlaps one of the An orbital from each F overlaps one of the spsp22 hybrids to form a B-F hybrids to form a B-F bond. bond.

B

F

F

F

B

F

F

F

rearrange electronshydridize orbs.

unused porbital

three sp2 hybrid orbitals

2 p2 s

120o

threesp2 hybridorbitals•

3535

spsp

• Figure Figure 10.11, page 448, & Figure 10.9 (3rd , page 448, & Figure 10.9 (3rd ed.) illustrates the outcome of hybridizing an ed.) illustrates the outcome of hybridizing an s and a p orbital to produce two sp hybrid s and a p orbital to produce two sp hybrid atomic orbitals with a linear geometry. atomic orbitals with a linear geometry.

• BeFBeF22 is an example of this type hybridization. is an example of this type hybridization.

• Predict the hybridization and geometry for Predict the hybridization and geometry for PFPF33 and BeH and BeH22. Describe the sigma bonds in . Describe the sigma bonds in each molecule. each molecule.

• We would expect the first to be spWe would expect the first to be sp33 hybridized, but it actually uses the 3p atomic hybridized, but it actually uses the 3p atomic orbital (3rd period) instead and has orbital (3rd period) instead and has approximately 90approximately 90oo bond angles. bond angles.

3636

Figure 10.11

36

3737

Orbital HybridizationOrbital HybridizationOrbital HybridizationOrbital Hybridization

BONDSBONDS SHAPESHAPE HYBRID REMAINHYBRID REMAIN

22 linear linear sp sp 2 p’s2 p’s

33 trigonal trigonal sp sp22 1 p1 p planar planar

44 tetrahedral tetrahedral sp sp33 nonenone

3838dspdsp33 and d and d22spsp33

• These hybridizations require five (5) and six These hybridizations require five (5) and six (6) atomic orbitals respectively and produce (6) atomic orbitals respectively and produce an equal number of hybrid atomic orbitals. an equal number of hybrid atomic orbitals. The electronic geometries are trigonal-The electronic geometries are trigonal-bipyramidal, and octahedral. bipyramidal, and octahedral.

• Figure Figure 10.12 provides an overview of these provides an overview of these cases and a review of the others. (page 450) cases and a review of the others. (page 450)

• Examples 10.3 & 4 cover PFExamples 10.3 & 4 cover PF55 and others. and others.

• Describe the hybridization, bonding, and Describe the hybridization, bonding, and

geometry for geometry for SFSF44 and SF and SF66..

3939

Figure 10.12

4040

Multiple BondingMultiple Bonding

• The second type of covalent bond is the The second type of covalent bond is the p p bondbond..

• The The pi bond (p)pi bond (p) results from the sideways results from the sideways overlap of two atomic p orbitals. The electron overlap of two atomic p orbitals. The electron density is above and below the plane. density is above and below the plane.

• The second bond between two atoms is always The second bond between two atoms is always a p bond as is the third bond in the case of a a p bond as is the third bond in the case of a triple bond.triple bond.

• Figures 11.8 Figures 11.8 (2nd ed.)(2nd ed.) & 10.13, 10.14, 10.16 and & 10.13, 10.14, 10.16 and models.models.

4141

Figure 10.13

4242Figure 10.14

4343

Figure 10.16

2 p bonds

4444

Bonding in GlycineBonding in Glycine

4545

Multiple BondsMultiple BondsMultiple BondsMultiple BondsConsider ethylene, CConsider ethylene, C22HH44

H H

C

H H

sp2120o

C

4646

Sigma Bonds in CSigma Bonds in C22HH44Sigma Bonds in CSigma Bonds in C22HH44

H H

C

H H

sp2120o C

4747

pp Bonding in C Bonding in C22HH44pp Bonding in C Bonding in C22HH44

The unused p orbital on each C atom contains an The unused p orbital on each C atom contains an electron and this p orbital overlaps the p orbital on the electron and this p orbital overlaps the p orbital on the neighboring atom to form the p bond. (See Fig. 10.13)neighboring atom to form the p bond. (See Fig. 10.13)

p orb.for bond

3 sp 2

hybrid

orbitals

2p2s

4848

Multiple BondingMultiple Bondingin Cin C22HH44

Multiple BondingMultiple Bondingin Cin C22HH44

4949

Consequences of Multiple BondingConsequences of Multiple Bonding

Restricted rotation around C=C bond.Restricted rotation around C=C bond.

5050

Multiple BondingMultiple Bonding

• Describe the hybridization, bonding, and Describe the hybridization, bonding, and geometry for Hgeometry for H22CO and HCN. Also do a CO and HCN. Also do a valence bond valence bond bonding diagram for each.bonding diagram for each.

• Figure Figure 10.15 for H for H22CO bonding.CO bonding.

• OO33, ozone, is an excellent example of pi , ozone, is an excellent example of pi resonance and a need for a better theory, resonance and a need for a better theory, the delocalized molecular theory. the delocalized molecular theory.

5151Figure 10.15

5252

Isomers Resulting from p BondingIsomers Resulting from p Bonding

• Since the pi bond is not free to rotate, two Since the pi bond is not free to rotate, two isomer are created, the isomer are created, the ciscis and the and the trans trans. .

• See page 457 and Figure See page 457 and Figure 10.18..

• The cis structure has the same atoms on the The cis structure has the same atoms on the same side of the double bond.same side of the double bond.

• The trans isomer has the atoms across the The trans isomer has the atoms across the double bond diagonally. double bond diagonally.

• There is a third possible isomer which has There is a third possible isomer which has both terminal atoms on the same central both terminal atoms on the same central atom, but this is a structural isomer. atom, but this is a structural isomer.

• Illustrate with CIllustrate with C22HH22BrBr22. .

5353

Figure 10.18

5454

Isomers of CIsomers of C22HH22BrBr22

Trans

Cis

5555

• MOLECULAR MOLECULAR ORBITAL THEORY — ORBITAL THEORY — Robert Mullikan (1896-Robert Mullikan (1896-1986)1986)

• valence electrons are valence electrons are delocalizeddelocalized

• valence electrons are valence electrons are in orbitals (called in orbitals (called molecular orbitals) molecular orbitals) spread over entire spread over entire molecule.molecule.

Two Theories of BondingTwo Theories of Bonding

5656

BenzeneBenzene

• The bonding p in benzene, CThe bonding p in benzene, C66HH66, can be , can be explained using resonance, but that explained using resonance, but that explanation leaves as many questions as explanation leaves as many questions as answers. answers.

• A theory involving delocalization of A theory involving delocalization of bonding p electrons is needed: bonding p electrons is needed:

The M.O. Theory.The M.O. Theory.

• Figure 10.19 and 3rd ed.Figure 10.19 and 3rd ed.

5757

Figure 10.19

57

585810.3 MOLECULAR ORBITAL THEORY10.3 MOLECULAR ORBITAL THEORY

• Instead of considering atomic orbitals or Instead of considering atomic orbitals or hybrid atomic orbitals localized on a single hybrid atomic orbitals localized on a single atom, we consider a set of orbitals atom, we consider a set of orbitals common to the whole molecule, common to the whole molecule, delocalizeddelocalized M.O. theory.M.O. theory.

• In the case of In the case of localizedlocalized M.O. theory, the M.O. theory, the orbitals are common to the two atoms orbitals are common to the two atoms being bonded.being bonded.

• This new theory is needed to explain the This new theory is needed to explain the paramagnetic property of oxygen and paramagnetic property of oxygen and certain other diatomic molecules. certain other diatomic molecules.

• ParamagneticParamagnetic species have one or more species have one or more unpaired electrons. unpaired electrons.

• DiamagneticDiamagnetic species have no unpaired species have no unpaired electrons.electrons.

5959

Paramagnetic/diamagneticParamagnetic/diamagnetic

6060

MOLECULAR ORBITAL THEORYMOLECULAR ORBITAL THEORY

• Molecular orbitals, like atomic orbitals, are Molecular orbitals, like atomic orbitals, are assigned electrons according to theassigned electrons according to the Pauli Pauli principle and principle and Hund'sHund's rule. rule.

• The electrons fill the lowest energy orbitals The electrons fill the lowest energy orbitals first with out pairing, then pair. first with out pairing, then pair.

• Once these orbitals are filled, electrons are Once these orbitals are filled, electrons are assigned to the next highest energy assigned to the next highest energy orbitals.orbitals.

6161There are four principles in the M. O. T.There are four principles in the M. O. T.

1)1) The number of molecular orbitals is The number of molecular orbitals is always equal to the number of atomic orbitals always equal to the number of atomic orbitals for the atoms forming the molecule (or ion). for the atoms forming the molecule (or ion). For every bonding molecular orbital there is a For every bonding molecular orbital there is a corresponding antibonding orbital. corresponding antibonding orbital.

• Figure 10.21, page 461. Figure 10.21, page 461. • In this case we see a sIn this case we see a sbb and a s*. The bonding and a s*. The bonding

orbitals result from an in phase combination of orbitals result from an in phase combination of the atomic orbitals, and the antibonding the atomic orbitals, and the antibonding orbitals result from an out of phase orbitals result from an out of phase combination to the atomic orbitals. combination to the atomic orbitals.

6262Figure 10.21

6363

There are four principles in the M. O. T.There are four principles in the M. O. T.

2)2) The bonding molecular orbital is The bonding molecular orbital is always lower in energy than the parent always lower in energy than the parent atomic orbitals and stabilizes the atomic orbitals and stabilizes the molecule. The antibonding orbital is molecule. The antibonding orbital is always higher in energy that the parent always higher in energy that the parent atomic orbitals and destabilizes the atomic orbitals and destabilizes the molecule.molecule.

• Figure 10.22, page 461.Figure 10.22, page 461.

–This figure illustrates the bonding for HThis figure illustrates the bonding for H22..

6464

Figure 10.22

64

6565

There are four principles in the M. O. T.There are four principles in the M. O. T.

3)3) Electrons in the molecule are Electrons in the molecule are assigned to orbitals of successively higher assigned to orbitals of successively higher energy according to the Pauli principle and energy according to the Pauli principle and Hund's rule. Hund's rule.

Bonding orbitals stabilize and antibonding Bonding orbitals stabilize and antibonding orbitals destabilize the molecule. orbitals destabilize the molecule.

4)4) Atomic orbitals combine most Atomic orbitals combine most effectively to form molecular orbitals when effectively to form molecular orbitals when the atomic orbitals have similar energies. the atomic orbitals have similar energies.

6666

Bond orderBond order

• Bond order is defined as the number of net Bond order is defined as the number of net bonding electrons divided by two. bonding electrons divided by two.

B.O. = (# bonding eB.O. = (# bonding e-- - # antibonding e - # antibonding e--)/2.)/2.

• The bond order can be fractional, but is never The bond order can be fractional, but is never negative. negative.

• A bond order of zero indicates that the A bond order of zero indicates that the molecule (ion) is not stable. molecule (ion) is not stable.

• Example 10.7 and Exercise 10.7.Example 10.7 and Exercise 10.7.

6767

ContinuedContinued

• Do a molecular orbital diagram and Do a molecular orbital diagram and molecular orbital configuration for: molecular orbital configuration for:

• HH22- - and Heand He22

++..

• Figure Figure 10.24, page 463, illustrates the , page 463, illustrates the bonding for Libonding for Li22..

• Do a molecular orbital diagram and Do a molecular orbital diagram and molecular orbital configuration for: Hemolecular orbital configuration for: He22

- -

and Beand Be22++..

• Example 10.8 and Exercise 10.8.Example 10.8 and Exercise 10.8.

6868

Figure 10.24Figure 10.24

6969Molecular Orbitals for Homonuclear Diatomic Molecular Orbitals for Homonuclear Diatomic MoleculesMolecules

• P orbitals can be used for both s molecular P orbitals can be used for both s molecular orbitals and p molecular orbitals. Figure orbitals and p molecular orbitals. Figure 10.25 and 10.26, pages 464. and 10.26, pages 464.

• This gives rise to a new form of molecular This gives rise to a new form of molecular orbital diagram.orbital diagram.

• Figure Figure 10.27, page 465. , page 465.

• Notice the differences with the p bonding Notice the differences with the p bonding orbitals lower in energy than the sorbitals lower in energy than the s2p2p bonding bonding orbitals, but the reverse order for the orbitals, but the reverse order for the antibonding orbitals. antibonding orbitals.

7070

Figure 10.25

7171Figure 10.26

7272Figure 10.27

7373Molecular Orbitals for Homonuclear Diatomic MoleculesMolecular Orbitals for Homonuclear Diatomic Molecules

• O.H.O.H. Table 10.1 page 466 for the second Table 10.1 page 466 for the second period molecules. period molecules. Examples and Exercises 10.9.Examples and Exercises 10.9.

• For For heteronuclear heteronuclear diatomic ions and diatomic ions and molecules, the element with the higher molecules, the element with the higher electronegativity always has the lower electronegativity always has the lower energy atomic orbitals, and receives the energy atomic orbitals, and receives the additional electrons if the ion is an anion.additional electrons if the ion is an anion.

• Do a molecular orbital diagram and molecular Do a molecular orbital diagram and molecular orbital configuration for: NO, OForbital configuration for: NO, OF--,, and CNand CN++.. Give Give the bond order and magnetic properties for the bond order and magnetic properties for each.each.

7474

Delocalized Molecular TheoryDelocalized Molecular Theory

• OO33 is an excellent example. is an excellent example.

• Figure 10.28 page 469. page 469.

• The molecule has one The molecule has one p p bond and two bond and two bonding sites. bonding sites.

• The bond order is 1.5, with 1 sigma bond The bond order is 1.5, with 1 sigma bond between each oxygen atom and one between each oxygen atom and one p p bond spread between the three atoms. bond spread between the three atoms.

• The other pair of electrons is in a The other pair of electrons is in a pp nonbonding orbital. nonbonding orbital.

• The molecule is diamagnetic.The molecule is diamagnetic.

7575

Figure 10.28

See the M.O. diagram page 468.

0 e-

2 e-

2 e-

7676

Figure 10.19

Benzene Delocalized electrons

7777Figure 10.29

Benzene

M.O. diagram

7878

7979

10.410.4 METALS AND SEMICONDUCTORSMETALS AND SEMICONDUCTORS

• The atomic orbitals of metals form The atomic orbitals of metals form delocalized, conducting bands. delocalized, conducting bands.

• Figure Figure 10.30, page 470. , page 470.

• In the case of metals with s and p orbitals, In the case of metals with s and p orbitals, these bands overlap. these bands overlap.

• This is called the Band theory.This is called the Band theory.

• Use the Band theory to show how Mg and Al Use the Band theory to show how Mg and Al are conductors.are conductors.

8080

Figure 10.30

Sodium as a conductor

8181

Lithium, a metal conductorLithium, a metal conductor

8282

METALS AND SEMICONDUCTORSMETALS AND SEMICONDUCTORS

• Nonmetals hybridize first and then form Nonmetals hybridize first and then form two bands, the valence band and the two bands, the valence band and the conduction band, with a gap between conduction band, with a gap between them. See Figure 10.32, page 471. them. See Figure 10.32, page 471.

• If the gap is small as in Si and Ge which If the gap is small as in Si and Ge which are semiconductors, the electrons are are semiconductors, the electrons are easily promoted from one band the other easily promoted from one band the other allowing for conduction.allowing for conduction.

8383

Doping Si with AlDoping Si with Al

8484

METALS AND SEMICONDUCTORSMETALS AND SEMICONDUCTORS

• Use the Band theory to show how C and Ge Use the Band theory to show how C and Ge behave.behave.

• If Si and Ge are doped with atoms having 3 If Si and Ge are doped with atoms having 3 or 5 valence electrons, p and n type or 5 valence electrons, p and n type semiconductors are created.semiconductors are created.

• Figure 10.34, page 472.Figure 10.34, page 472.

8585Figure 10.34

85