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Class 3Class 3 General Review ofGeneral Review ofClass 3Class 3 General Review ofGeneral Review of

Atomic BondingAtomic BondingAtomic BondingAtomic Bonding

READING Chapter 2 in DeGraef and McHenry, pp. 38-48.

HANDOUT from Cha ter 2 of R.J.D. Tille Understandin Solids: The Science of Materials

(Wiley, New York, 2004).

ADDITIONAL REFERENCES:

Chapter on bonding from any Introduction to Materials book.

Prof. M.L. Weaver

Chapter 1 in Rohrer

Chapter 8 in Bloss

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The next 16 view ra hs are a

review of the previous lecture.

Prof. M.L. Weaver

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Atomic Structure (Freshman Chem.)Atomic Structure (Freshman Chem.)

atom electrons 9.11 x 10-31 kgprotons

neutrons atomic number= # of protons in nucleus of atom

1. 7x10 g

= # of electrons of neutral species

= = = 12

Atomic wt = wt of 6.022 x 1023 molecules or atoms

1 amu/atom = 1g/mol

C 12.011

Prof. M.L. Weaver56

H 1.008 etc.RECALL/REVIEW

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AtomicStructureAtomicStructure Valence

electrons

determine

all

of

the

following

properties

1) Chemical

2) Electrical

3) Thermal

4) Optical

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ImpactofBondingonPropertiesImpactofBondingonProperties

The

Bohr

model

shows

electronsrevolving

discreteenergylevels

Quantummechanicsgovernhowthese

electronsfill

the

specific

levelsandhowtheyElectrons revolve around the nucleus in discrete

energy levels. For an electron to change energy

levels it must either gain or lose specificamounts of energy.

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our uantum um ersour uantum um ers

the electrons.

general shape of the electron cloud.(*aka. Subsidiary or azimuthal quantum number)

Third Quantum Number** (ml or ml) indicates the

spatial orientation of the electron cloud.

(**aka. Magnetic quantum number)

Fourth Quantum Number*** (Ms) represents the spin of

the individual electrons.

(***aka. Spin quantum number) RECALL/REVIEW

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econ uantum um erecon uantum um er Someoftheenergylevels

splitintosublevels(orbitals/suborbitals)

follows

First=s(l=

0)

= =1

Third=d(l=2)

Fourth=f(l=3)

Etc l=n1but:

Max.numberofsuborbitals=principlequantumnumber

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ThirdQuantumNumberThirdQuantumNumber

Indicatesthespatialorientationoftheelectroncloud.

RECALL/REVIEW

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=

ShapesoftheElectronOrbitalsShapesoftheElectronOrbitals

l = 1

ml = 0 ml = +1 ml = -1

l = 2

ml = 1ml = 2 ml = - ml = -

Differentshapescorrespondingtodifferent

ml = 0

Chapter1 TypesofMaterials,

ElectronEnergy

Bands,

and

ChemicalBonds

suborbitals.

Veryimportant

in

bonding

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FourthQuantumNumberFourthQuantumNumber

The

fourth

quantum

number

(spin)

has

no

relationshiptotheotherthree.

ThetwopossiblevaluesareMs =+or

Electronswith

the

same

value

have

parallelspins

whilethoseofoppositevalueshaveoppositespins ThePauli exclusion principle showsthatnotwo

e ectronscan avet esameseto ourquantumnumbers. Nomorethantwoelectronswithopposite

.

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Electron Energy States have discrete energy states

tend to occu lowest available ener state.

Electrons...

4p4d

N-shell n = 4

3d

4s

3s3p M-shell n = 3Energy

Ada ted from Fi . 2.4,

2s2p

L-shell n = 2Callister & Rethwisch 8e.

Chapter 2 - 65

1s K-shell n = 1

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SURVEY OF ELEMENTS Most elements: Electron configuration not stable.Electron configurationAtomic #Element1s 1

(stable)1s 22Helium1s 22s 13Lithium1s 22s24Beryllium

2 2 1

...1s 22s 22p 26Carbon

...

1s 22s 22p 6 (stable)10Neon

. ,

Callister & Rethwisch 8e.

...

s s p s11Sodium1s 22s 22p 63s 212Magnesium1s 22s 22p 63s 23p 113Aluminum

...

1s 22s 22p 63s 23p 6 (stable)...

1s 22s 22p 63s 23p 63d 10 4s 24p 6 (stable)

18...

36

Argon...

Krypton

Chapter 2 - 66

Why? Valence (outer) shell usually not filled completely.

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Electronic Configurationsex: Fe - atomic # = 26 1s2 2s2 2p6 3s2 3p6 3d6 4s2

valenceelectrons

4p4d N-shell n = 4

4s

Adapted from Fig. 2.4,

Callister & Rethwisch 8e.

3sp -s e n =Energy

2sp L-shell n = 2

Chapter 2 - 68

-

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ReviewReview

Aufbau PrincipleAufbau Principle

ReviewReview

Aufbau PrincipleAufbau Principle Energy levels of quantum shells dont fill in strictnumerical order. Thus there are deviations.

TheAufbau principle is a graphical device used topredict deviations from expected ordering.

K (2)

SHELL (# e--)

L (8)

M (18)

N 32

See this website for a good review

O (50)

P (72)

Prof. M.L. Weaver 2011CengageLearningEngineering.AllRightsReserved.

http://www.avogadro.co.uk/light/aufbau/aufbau.htm

s2 p6 d10 f14 g18 h22 i26

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Aufbau ExampleAufbau Example contdcontdAufbau ExampleAufbau Example contdcontd Electrons will usually occupy every orbital singly

.

a om c num er :

1s2

2s2

2p3

Each of the threep orbitals in theL shell contains one

e ec ron as oppose o one or a con a n ng oneelectron and one containing zero electrons.

Prof. M.L. Weaver

See this website for a good reviewhttp://www.avogadro.co.uk/light/aufbau/aufbau.htmRECALL/REVIEW

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OptimalDistancebetweenAtomsOptimalDistancebetweenAtoms Interactionsareblendsof

attractiveand

repulsive

forces

Bothforcesareafunctionof

distance

Thepointatwhichthedifferencebetweenthe

attractive repulsive

forces

is

greatestrepresentstheo timaldistance

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PolarityPolarity Whendifferentmolecules

interact,one

has

agreater

affinit forelectronsthantheother.

ee ec ron ens yo atypicalpolarbondisshownontheright.

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ElectronegativityElectronegativity

Electronegativity

is

the

ability

of

an

atom

to

accept

electrons.

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Electronegativity Ranges from 0.7 to 4.0, Large values: tendency to acquire electrons.

Smaller electronegativity Larger electronegativity

Chapter 2 - 78

Adapted from Fig. 2.7, Callister & Rethwisch 8e. (Fig. 2.7 is adapted from Linus Pauling, The Nature of the

Chemical Bond, 3rd edition, Copyright 1939 and 1940, 3rd edition. Copyright 1960 by Cornell University.

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ReviewReviewReviewReview

Metallicity (electropositivity):

Tendency of an atom to donate electrons to metallic or

ionic bonds. This is opposite of electronegativity.

ncreases as an atom n s t va ence e ectrons w t re uce

strength (i.e., as valence electron-nucleus separation increases,

binding force decreases). As you go from right to left on the periodic table, the valence

electron-nucleus separation is about the same, but nuclear charge

decreases (thus, binding force decreases).

Increases from top to bottom and from right to left of

periodic table.

Prof. M.L. Weaver

RECALL/REVIEW

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ReviewReviewReviewReview

Size:

.

REMEMBER that cations (+) are smaller than protons(neutral), whereas anions (-) are larger.

Mass: ncreases w a om c num er e you now w y .

,these trends to predict bonding and properties.

Prof. M.L. Weaver

RECALL/REVIEW

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Types of BondingTypes of BondingTypes of BondingTypes of Bonding

IONIC0.9 3.0

METALLIC

Van der Waals

There are many models that describe

Prof. M.L. Weaver 2011CengageLearningEngineering.AllRightsReserved.

.

information in the next two lecture

modules. Please read them.

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RECALLRECALL

RECALLRECALL

21

41nm mx x

e

xnm is the electronegativity of the nonmetallic element

xm is the electronegativity of the metallic element

Assume: f > 0.5 (x > 1.7) ionic bonds

0.5 x 1.7 covalent bonds

Actual change from metallic to ionic/covalent is more

Prof. M.L. Weaver

complex. Thus we assign some elements as metalloid.

RECALL/REVIEW

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Primary BondingPrimary BondingPrimary BondingPrimary Bonding

Metallic Bond -- delocalized as electron cloud

Ionic-Covalent Mixed Bonding

% ionic character= %100x1 e (XA XB )2

4

whereXA

&XB

are Pauling electronegativities

Ex: MgO XMg =1.2XO =3.5

ionic73.4%(100%)xe1characterionic% 4)2.15.3(

2

Prof. M.L. Weaver

83RECALL/REVIEW

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Bonding GeneralizationsBonding Generalizations

RECAP

In ternary or more complex compounds, the fractional ionicity

can be determined b usin stoichiometricall wei hted avera es

for the values of xm

and/or xnm

, ex.: In4Sn

3O

12

nonmetallic character is continuous and complex, so much so

that many authors would refute the apparently arbitrary binarycategor zat on e ne t us ar.

It is more common to define a third class of elements, the

metalloids, which straddle the metalnonmetal boundary (e.g.:B, Si, Ge, As, Te, and Se).

Prof. M.L. WeaverRECALL/REVIEW

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BondingBonding Property InterrelationshipsProperty Interrelationships

However, a binary classification is nevertheless implemented because it has the

practical advantage of leading to a simple set of rules to determine bond types.

nce e on ype s e ne , e ype o a om c s ruc ure an proper es a e

solid might have can also be inferred.This is illustrated schematically:

When crossing metal-nonmetal

Prof. M.L. Weaver

oun ary, proper es c ange

dramatically with variation in

bonding:

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CovalentvsIonicBondingCovalentvsIonicBonding Thepolarityofacovalent

bondis

the

partial

ionic

character

Realbonds

lie

somewhere

e ween on can cova en

Thedifferencein

electronegativitycorresponds

directlytothepercentioniccharacterofthebond

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