ki1101-2012-kd lec05a chemicalbondinggeneralconcepts

8/11/2019 KI1101-2012-KD Lec05a ChemicalBondingGeneralConcepts

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Chapter 9The Basic of Chemical BondingThe Basic of Chemical Bonding


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Summary HighlightsSummary Highlights

Ionic Bonding Electronegativity and Polar Bonds

Reactivity and Electronegativity

Lewis Symbol and Lewis Structures Formal Charges

Coordinate Covalent Bonding

Resonance


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!" Electron trans#er leads to the #ormation o# ionic com$ounds %

Lattice Energy& 'Lattice Energy& '

Com$ound IonsLattice

Energy )*+

mol,"-

LiCl Li.and Cl, /0

1aCl 1a.and Cl, 22

3Cl 3.and Cl, 245

LiF Li.and F, "4%%

CaCl6 Ca6.and Cl, 660

7lCl% 7l%.and Cl, 0/56

Ca8 Ca

6.

and 8

69

%/4"7l

68

% 7l%.and 869 "0&5":

Formation o# gaseous ions #rom an ionic solid

7;By)s-


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!" Electron trans#er leads to the #ormation o# ionic com$ounds /

Born Haber Cycle #or 1aClBorn Haber Cycle #or 1aCl

61a)s-. Cl6)g-< 61aCl)s-=hat has to ha$$en>

Sublime 1a? @HsubA "42!

*+mol

Ionie 1a? IE"A /50!/

*+mol

Brea* Cl bond? D) Cl9Cl-A

"6"!% *+mol

Ionie Cl? E7 A 9%/!

*+mol

Form bond? 9' A 922

*+mol


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!" Electron trans#er leads to the #ormation o# ionic com$ounds 0

' vs! Bond Formation Energy' vs! Bond Formation Energy

he #ormation o# one mole o# solid #rom gaseous ions)ionic bond formation- is numerically the same as the

lattice energy

1a.)g-. Cl9)g- < 1aCl)s-. 22 *+

Since this is energy released& the value #or this $rocesswould be G'

Smaller ions have greater attractive #orces& as have those

with higher charges

krqqU 6"


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!" Electron trans#er leads to the #ormation o# ionic com$ounds :

Electron Con#igurations IonsElectron Con#igurations Ions

"! he #irst electrons to be lost by an atom or ionare always those #rom the shell with the largest

value o# n

6! 7s electrons are removed #rom a given shell&

they come #rom the highest9energy occu$ied

subshell #irst be#ore any are removed #rom a

lower9energy subshell!

%! =ithin a given shell& the energies o# thesubshells vary as #ollows?spdf!


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!" Electron trans#er leads to the #ormation o# ionic com$ounds 2

Electron Con#igurations 8# CationsElectron Con#igurations 8# Cations

ain rou$ metals lose the electrons in theirhighest energysubshell#irst to achieve the

$reviously #illed noble gas )the octet rule-

rou$ Ia? J1oble gas coreKns"

Form ". ions to be isoelectronicwith noble gas coreelement

rou$ IIa? Jn!g!c!Kns6

Forms 6. ions

rou$ IIIa? Jn!g!c!Kns6n$"

Forms %. ions


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!" Electron trans#er leads to the #ormation o# ionic com$ounds

Electron Con#iguration o# CationsElectron Con#iguration o# Cations

ain rou$ metals lose the electrons in theirhighest energy subshell#irst! Elements in grou$

IIIa below 7l also #orm ". ions!

a ? J7rK /s6%d"4/$" 9 " e9 e9

869

1? JHeK6s66$%.>e9

1%9


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"49" Lewis heory? 7n 8verview"49" Lewis heory? 7n 8verview

Oalence e9

$lay a#undamental role in

chemical bonding!

e9trans#er leads to

ionic bonds. Sharing o# e9leads to

covalent bonds.

e- are trans#erred o#

shared to give each atoma noble gas con#iguration

the octet.


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Lewis SymbolsLewis Symbols

7 chemical symbol re$resents the nucleus and the

coree9!

ots around the symbol re$resent valence e-.

Si

1

P

7s

Sb

Bi

7l

Se

7r

I


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!6 Lewis symbols hel$ *ee$ trac* o# valence electrons "/

Lewis Structures 8# 7toms?Lewis Structures 8# 7toms?

he element symbol is imagined to have a bo;around it! he valence e9 are distributed aroundthe #our sides o# the bo;!

For the aQ grou$ elements& the grou$ number is

the number o# valence e9! For& 7l& a grou$ IIIa element& there are % valence

e9! Its Lewis structure is

7l


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!6 Lewis symbols hel$ *ee$ trac* o# valence electrons "0

he 8ctet Rulehe 8ctet Rule

Stable atoms tend to have #ull or e;actly hal#9#ullsublevels!

S$ecial stability is achieved in the noble gases&

which have #ull sublevels!

he octet ruleQ9 atoms will lose or gain e9 in

order to have e9 surrounding them as have the

noble gases!

H and He will need only 6 e9& thus #ollow theduet ruleQ!


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!6 Lewis symbols hel$ *ee$ trac* o# valence electrons ":

Lewis Structures For onatomic IonsLewis Structures For onatomic Ions

Because ions are #ormed by the gain or loss o# e9& theLewis structure indicates this change in the number o#valence e9

=e subtract the charge on the ion #rom the number o#

valence e9 and show these around the element symbol =e enclose the symbol in brac*ets and indicate the

charge

#or 1a.ion "9"A4

#or 869ion& :9)96-A

J 1a K.

J 8 K69


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!6 Lewis symbols hel$ *ee$ trac* o# valence electrons "2

Mour urnNMour urnN

How many electrons are to be shown on 1%9>7! %

B! 0

C! ! 1one o# these


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!6! Lewis symbols hel$ *ee$ trac* o# valence electrons "

Chemical BondsChemical Bonds

Ionic bondsresult #rom attractive #orces between

o$$ositely charged $articles

etal 9 nonmetal bonds are ionic because?

metals have low ioniation energies and easily lose e9to be

stable

non9metals have low electron a##inities

the #ormation o# the lattice stabilies the ions!

Na+ Cl -


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!6! Lewis symbols hel$ *ee$ trac* o# valence electrons "5

Ionic Com$oundsIonic Com$ounds

Ionic crystals: e;ist in a %9dimensional array o# cations and

anions called a lattice structure

Ionic chemical formulas? always

written as em$irical #ormula

)smallest whole number ratio o#

cation to anion-


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!6! Lewis symbols hel$ *ee$ trac* o# valence electrons 64

Ionic Com$ounds G Lewis StructuresIonic Com$ounds G Lewis Structures

Ionic com$ounds are #ormed by the attractionbetween o$$ositely charged ions

show each ion& se$arately& alternating charges

#or the ionic com$ound 36

S?

[ K ]+[ S ]2-[ K ]+


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!6! Lewis symbols hel$ *ee$ trac* o# valence electrons 6"

Mour urnNMour urnN

=hich o# the #ollowing correctly describes a #ormula unit768>

7! J7.KJ 869KJ 7.K

B! J 869

KJ 7.

K J 869

KC! J 7.K J 7.K J 869K

! 7ll o# these are $ossible


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!% Covalent bonds are #ormed by electron sharing 66

Chemical BondsChemical Bonds

Covalent bonds#orm when atoms share valence electrons inthe region o# s$ace created by orbital overla$

1onmetal 9 nonmetal bonds are shared or covalent bonds

because neither element easily loses e9

Symbolied by a line between the atoms

ay include u$ to three $airs o# e9?

two $airs #orm a double bond AM

three $airs #orm a tri$le bond M

H H:


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!% Covalent bonds are #ormed by electron sharing 6%

Potential Energy vs! Internuclear istance In HPotential Energy vs! Internuclear istance In H66


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!% Covalent bonds are #ormed by electron sharing 6/

Bond issociation Energy& Bond issociation Energy&

he energy needed to brea* one mole o# a bond ina covalent molecule in the gas $hase is called

bond dissociation energy& and is symbolied

varies with bond ty$e )single& double& tri$le-

varies with the atoms involved

he #ormation o# bonds stabilies the structure

energetically


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!% Covalent bonds are #ormed by electron sharing 60

olecules 8#ten 8bey he 8ctet Ruleolecules 8#ten 8bey he 8ctet Rule

Share e9

to gain octet ay #orm single& double

or tri$le bonds

Each atom has e9

surrounding it


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!/ Covalent bonds can have $artial charges at o$$osite ends 6:

1ot 7ll 7toms Share Electrons Eually1ot 7ll 7toms Share Electrons Eually

=hile electrons in a covalent bond are shared& the

electrons are not evenly distributed between the twonuclei

Electronegativity is a measure o# the attractive #orcethat one atom in a covalent bond has #or the electrons o#

the bond


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!/ Covalent bonds can have $artial charges at o$$osite ends 62

Bond i$olesBond i$oles

7toms with di##erent electronegativity values willshare electrons uneually

Electron density is uneven& with a higher chargeconcentration around the more electronegative

atom Bond dipolesindicate with delta )T- notation that

a $artial charge has arisen

Partial negative )T9- charge is assigned to the

more electronegative element Such a bond is termed apolar bond


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Learning Chec*?Learning Chec*?

'sing delta notation& indicate the bond $olarity #orthe #ollowing?

F9Cl

C98

C91

19Cl

T. T9

T. T9

T9 T.

T9 T.


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Mour urnNMour urnN

=hich o# the #ollowing is the correct assignment o#the $artial charges in the bond 898>

7! 8)T.-98)T9-

B! 8)T9-98)T.-

C! 8)T9-98)T9-

! 1one o# these It is non9$olar


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!/ Covalent bonds can have $artial charges at o$$osite ends %4

i$ole omenti$ole oment

UAVr A charge in coulombs& C

rA distance se$arating charges& m

" A%!%/V"4%4C m


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!/ Covalent bonds can have $artial charges at o$$osite ends %"

Learning Chec*Learning Chec*

he C8 molecule has a di$ole moment o# 4!"" and a bondlength o# ""% $m! =hat is the amount o# charge& in

electronic charge units& on either end o# the bond>

CD

mC-"4)60!%

"

-"4)%/!%

m"4

$m

$m""%

4!""

rWrXW

6"%4

"6


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!0 he reactivities o# metals and nonmetals can be related to their %6

8;idation 7nd he Periodic able8;idation 7nd he Periodic able


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!: rawing Lewis structures is a necessary s*ill %%

Lewis Structures For Covalent StructuresLewis Structures For Covalent Structures

7rrange atoms around central atom

Sum valence electronsX divide by 6 to #ind $airs

Bond atoms to central atom with a single bond

bond $airs are shown as a lineX non9bonding e9 are

shown as dots

Com$lete the octet #or central atom

istribute e9 to com$lete the octet #or any attached

atoms $lace e;tra electrons on central atom

#orm doubletri$le bonds i# necessary to com$lete octet

atoms andor reduce #ormal charges


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!: rawing Lewis structures is a necessary s*ill %/

E;ce$tions o 8ctet RuleE;ce$tions o 8ctet Rule

H and He #ollow the duet rule B usually has only : surrounding electrons

Be bonds with Yust / surrounding electrons

Elements in the %rd

$eriod and higher contain dQorbitals& so may accommodate more than ! his

is not the most li*ely situation& but can occur!

he result is an e;$anded octetQ


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!: rawing Lewis structures is a necessary s*ill %0

Choosing 7 Central 7tomChoosing 7 Central 7tom

Central atom is the uniue atom I# there is more than one element contributing only

one atom& the element #arther le#t on the $eriodic

table is the central atom

H is always terminal

Halogens are usually terminal

C is always central


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!: rawing Lewis structures is a necessary s*ill %:

raw the Lewis Structure #orraw the Lewis Structure #or1F1F%%

=hich atom is the central atom> How many valence e9 does 1F%have>

Bond 1 to F

Satis#y the 1 octet How many e9remain> istribute them on F to

com$lete octet!

oes each atom have an octet> I# not& multi$lebond!

N

F

:

:..

5 + 3(7)=26 e-

FF:

:

:

:

: :

:


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raw the Lewis Structureraw the Lewis Structure

C86

HC1

NC

H

OC

O


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E;$anded octet may occur #or atoms below theE;$anded octet may occur #or atoms below the

66ndnd$eriod$eriod

For e;am$le& SF:

S

F

F

F

F

F

F


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!: rawing Lewis structures is a necessary s*ill /4

Carbon Hates Lone PairsNCarbon Hates Lone PairsN

7#ter you have drawn your structure& chec* to see i#

carbon has any lone )unshared- e9 $airs

i# it does& chec* to see i# there is any other arrangement

wo common s$ecies e;ist with lone $airs on C? C19&

and C8! =hat are their Lewis structures>


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!: rawing Lewis structures is a necessary s*ill /"

=rite Electron ot Structures For=rite Electron ot Structures For

e8F/

SbCl0

HC8%9


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Mour urnNMour urnN

raw the Lewis structure #or eF:! How manybonding $airs are there>

7! :

B!

C! 60

! 1one o# these


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!: rawing Lewis structures is a necessary s*ill /%

Bond Length 7nd Bond 8rderBond Length 7nd Bond 8rder

Bond lengthis the distance between the nuclei o# thetwo atoms in a bond

Bond orderis the number o# electron $airs shared

between the atoms

7s bond order increases& the bond length decreases and

the bond energyincreases& $rovided we are com$aring

bonds between the same elements

Bond Bond Length )$m- Bond Energy )*+mol-

CGC "0/ %/

CZC "%/ :"0

CC "64 "6


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!: rawing Lewis structures is a necessary s*ill //

Formal ChargesFormal Charges

FC A J[ Oalence e9K GJ [ bonds . [ unshared e9K

Sum o# FC A charge on $article

Calculated #or all atoms in the structure

7 good structure should have ?

small #ormal charge values )4 is best- #ew atoms with a non9ero #ormal charge

most electronegative element is 4 or negative

no adYacent $ositive or negative #ormal charges


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Learning Chec*N?Learning Chec*N?

: [[

+

Calculate he Formal Charges 8n

Each 7tom


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!: rawing Lewis structures is a necessary s*ill /:

Mour urnNMour urnN

=hat is the #ormal charge on 1 in 1H/.

>7! 4

B! ."

C! 9"! .6

E! 1one o# these


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Coordinate Covalent BondsCoordinate Covalent Bonds

In most covalent bonds& each atom su$$lied one o#the e9in the bond $air

=hen the same atom su$$lies both e9& bond is

called a coordinate covalent bond.

Com$are 1 to 1 in 1H/! Its lone $air site is now

occu$ied by a bond? the bond is coordinate!

e;! 1 vs 1 in 1H/

1 HHH1

H

.


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!2 Resonance a$$lies when a single Lewis structure #ails /

Isomerism and Resonance? Oariations on aIsomerism and Resonance? Oariations on a

hemeheme

Structures with the same #ormula in which theatoms are in di##erent arrangement are termed

isomers

I# the atoms are in the same geometric

con#iguration but the electrons are arrangeddi##erently& the structures are termed

resonance structures

How do you *now i# your structure isreasonable> Chec* theformal chargesN


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!2 Resonance a$$lies when a single Lewis structure #ails /5


=hich is better>


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!2 Resonance a$$lies when a single Lewis structure #ails 04

Evidence o# Resonance? Carbonate& C8Evidence o# Resonance? Carbonate& C8%%6969

C:O..

:O:

..O:

..

C:O..

..:O:

..O:

C:O..

..:O:

..O:

....

6969

69

..0 0

0

0

0 0

-1 -1

-1

-1 -1

-1

hree $ossible ways o# writing the Lewis structure

Structures have eually good #ormal chargedistribution

E;$erimental bond lengths are the same

7ctual molecule must be a blend


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!2 Resonance a$$lies when a single Lewis structure #ails 0"

Resonance Structures? he 1itrate Ion& 18Resonance Structures? he 1itrate Ion& 18%%99

N OO

O

0

-1

+ 1

-1

N OO

O

-1

-1

0

+ 1

ONO

O 0

-1

-1 + 1


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!2 Resonance a$$lies when a single Lewis structure #ails 06


raw three structures #or 168! Identi#y the best!

raw three resonance structures #or the $hos$hateion& P8/

%9! Identi#y the best!


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Mour urnNMour urnN

=hich is the best structure #or the sul#ate ion>

7! B! C! !

ki1101-2012-kd lec05a chemicalbondinggeneralconcepts

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