Lewis electron-dot Structures Chemical Bonding, again B

Chemical Bonding, again

• ionic bonding (in salts): transfer of e-

• covalent bonding (organic molecules, non-metals): sharing e-

• metallic bonding: electron pooling (delocalization)

Lewis electron-dot Structures

Li

Na

Be

Mg

B

Al

C

Si

N

P

O

S

F

Cl

Ne

Ar

1A 2A 3A 4A 5A 6A 7A 8A

2

3

1. Determine the number of valence electrons

2. Place one dot at a time on four sides.

Lewis electron-dot Structures

Li

Na

Be

Mg

B

Al

C

Si

N

P

O

S

F

Cl

Ne

Ar

1A 2A 3A 4A 5A 6A 7A 8A

2

3

1. Determine the number of valence electrons

2. Place one dot at a time on four sides.

All correct: O OO

Octet Rule

when elements form compounds they attain a filled outer

shell of eight electrons

Li

Na

Be

Mg

B

Al

C

Si

N

P

O

S

F

Cl

Ne

Ar

1A 2A 3A 4A 5A 6A 7A 8A

2

3

(exceptions)

Ionic Bonding ModelSee sample problem 9.1

4Na + O2 ! 2Na2O

+ O

Na

NaNa+

Na+

O2-

3s

3s

3p

3p

2s 2p

2s 2p

2s 2p

2s 2p

3s 3p

3s 3p

inner shell

inner shell


4Na + O2 ! 2Na2O

+ O

Na

NaNa+

Na+

O2-

3s

3s

3p

3p

2s 2p

2s 2p

2s 2p

2s 2p

3s 3p

3s 3p

inner shell

inner shell


4Na + O2 ! 2Na2O

+ O

Na

NaNa+

Na+

O2-

3s

3s

3p

3p

2s 2p

2s 2p

2s 2p

2s 2p

3s 3p

3s 3p

inner shell

inner shell

+ O

Na

Na

+ O2Na+

2-

Lattice Energy: the Driving Force

LiFLi + 1/2F2 ! LiF


LiFLi + 1/2F2 ! LiF

Li (g) ! Li+(g) + e- "H(IE) = 520 kJ

F (g) + e- ! F- "H(EA) = -328 kJ

"Htotal = +192 kJ


LiFLi + 1/2F2 ! LiF

Li (g) ! Li+(g) + e- "H(IE) = 520 kJ

F (g) + e- ! F- "H(EA) = -328 kJ

"Htotal = +192 kJ

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Li (g) + 1/2F2(g)

"Hovapor= 161 kJ/mol

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Li (g) + 1/2F2(g)


Li (g) + F (g)

BE ("HoBE)=79.5 kJ/mol

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Li (g) + 1/2F2(g)


Li (g) + F (g)


Li+ (g) + F (g)

IE of Li ("Hof (Li+))

520.5 kJ/mol

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Li (g) + 1/2F2(g)


Li (g) + F (g)


Li+ (g) + F (g)


EA of F ["Hof (F

-(g))]

520.5 kJ/mol-328 kJ/mol

Li+ (g) + F¯ (g)

Born-Haber Cycle

Li (s) + 1/2F2(g)

E

n

t

h

a

l

p

y

H

LiF (s)

"Hoverall

"Hof=-617 kJ/mol

Li (g) + 1/2F2(g)


Li (g) + F (g)


Li+ (g) + F (g)


EA of F ["Hof (F

-(g))]

"Holattice (LiF(s))

520.5 kJ/mol-328 kJ/mol

-1050 kJ/mol

Li+ (g) + F¯ (g)

The Covalent Bond

H

H

HH+

HHH • + • H ! H : H

Lewis electron-dot structures

single bond, a shared pair of electrons

The Covalent Bond

H

H

HH+

HH

E

N

E

R

G

Y

kJ/mol

distance74 pm, bond distance

432

kJ/mol

H

H

+

The Covalent Bond

The Covalent Bond

bond length is proportional to atomic size

Types of Bonds and Bond

Order

single bond: bond order 1

H Br+ BrH H Br

double bond: bond order 2

O+ OOO O O

triple bond: bond order 3

N+ NNN N N

shared electrons


Order

O OCC

H

H

H

H


Order

O OCC

H

H

H

H

C O

H

H

formaldehyde


Order

O OCC

H

H

H

H

C O

H

H

formaldehyde

H O H O H O

HO-

hydroxide anion


Order

adenosine triphosphate, ATP

which atoms have an unshared pair of electrons, and how many?

C C

C

O

C

CH2

H

N

H

OHOH

C

C

N

C

NC

N

C

NH2

OP

O

O

O

PO

O

O

PO

O

O H

H

H H


Order

C C

C

O

C

CH2

H

N

H

OHOH

C

C

N

C

NC

N

C

NH2

OP

O

O

O

PO

O

O

PO

O

O H

H

H H

C C

C

O

C

CH2

H

N

H

OHOH

C

C

N

C

NC

N

C

NH2

OP

O

O

O

PO

O

O H

H

H HOHPO

O

O

"Hrxn = -31 kJ/mol H2O

Bond Energy

A—B ! A• + •B

"Hrxn= bond energy

in gas phase

Bond Length and Energy

C—F 133

C—Cl 177

C—Br 194

C—I 213

bond length

pm

C—F 453

C—Cl 339

C—Br 276

C—I 216

bond energy

kJ/mol


H—F 92

H—O 96

H—N 101

H—C 109

bond length

pm

H—F 565

H—O 467

H—N 391

H—C 413

bond energy

kJ/mol


C—C 154 347

C=C 134 614

C#C 121 839

bond length

pm

bond energy

kJ/mol

Electronegativity

Electronegativity

Electronegativity,

introduced by Pauling,

ranges from 0 to 4

Electronegativity

Electronegativity

F, fluorine - highest electronegativity, 4.0

Cs, Fr - lowest electronegativity, 0.7

generally, electronegativity is

inversely proportional to atomic size within a group

Electronegativity

O.N. and Electronegativity

more electronegative element will have the “negative sign”

electronegativity

As 2.0

S 2.5

H 2.1

Si 1.8

As2S3

SiH4silane



electronegativity

As 2.0

S 2.5

H 2.1

Si 1.8

As2S3

SiH4

-2+3

silane



electronegativity

As 2.0

S 2.5

H 2.1

Si 1.8

As2S3

SiH4

-2+3

+4 -1

silane

Bond Polarity

H F H F

!+ !-

Bond Polarity

N

H

H H

!+

!-N

H

H H!+!+

ammonia

Bond Polarity

generally, bond polarity is proportional to "EN

H—F "EN 1.9

H—Cl "EN 0.9

H—Br "EN 0.7

H —I "EN 0.1

po

larity

dec

reas

es

Bond Polarity

generally, bond polarity is proportional to "EN

H—F "EN 1.9

H—O—H "EN 1.4

NH3 "EN 0.9

po

larity

dec

reas

es

Polar Covalent/Ionic

"EN

Metallic Bonding

• is formed by a “sea” of electrons

• this electron “sea” holds the metal cations in the crystal

lattice

• electrons are highly delocalized and mobile

• good conductors of electricity and heat

Metallic Bonding

in gas phase: Na• + •Na ! Na:Na

metallicbond

Valence electrons

nuclei

coreelectrons

Metallic Bonding

sea of electrons

Metallic Bonding

! ductility of metals and the electron-sea model

Key Concepts in Chapter 9

! Lewis Electron-Dot Structures and Chemical Bonding

“octet rule”: when atoms bond, they gain, lose

or share electrons to attain a filled outer shell of

eight electrons (two for hydrogen)

O OCC

H

H

H

H

C O

H

H

pay attention to the unshared pairs of electrons


! Bonding: Ionic, Covalent, and Metallic

Born-Haber cycle and lattice energy

effects of ionic size and charge

Polar and Non-polar covalent bondstrends in bond length and strength

and polarity

bond order: single, double and triple

bonds


! Electronegativity

relative ability of a bonded atom to attract

the shared electrons

F F Br F H F

"EN = 0

non-polar

"EN = 1.2

polar

"EN = 1.9

more polar

Practice Problems

9.66. Use Lewis electro-dot symbols to represent the formation

of

(a) BrF3 from bromine and fluorine atoms

(b) AlF3 from aluminum and fluorine atoms

Practice Problems9.67. Even though so much energy is required to form a

divalent metal cation, the alkaline earth metals form halides

with a general formula of MX2, rather than MX. Let’s see

why.(a) Use the following data to calculate the "Ho

f of MgCl:

Mg(s) ! Mg (g) "Ho = 148 kJ

Cl2(g) ! 2Cl (g) "Ho = 243 kJ

Mg(g) ! Mg+(g) + e- "Ho = 738 kJ

Cl(g) + e- ! Cl- (g) "Ho = -349 kJ

"Holattice = -783.5 kJ

(b) Is MgCl stable relative to its elements? Explain.

(c) Use Hess’s law to calculate "Ho for the conversion of MgCl

to Mg and MgCl2 ("Hof of MgCl2 = -641.6 kJ/mol)

Practice Problems9.52. Use Figure 9.16 to indicate the polarity of each bond with

polar arrows:

(a) N—B

(b) N—O

(c) C—S

(d) S—O

(e) N—H

(f) Cl—O

Figure 9.16

EN

H 2.1

B 2.0

C 2.5

N 3.0

O 3.5

S 2.5

Cl 3.0

Practice Problems9.58. Rank the members of each set of compounds in order of

increasing polarity of their covalent bonds. Use polar arrows

to indicate the bond polarity of each.

(a) HBr, HCl, HI

(b) H2O, CH4, HF

(c) SCl2, PCl3, SiCl4

ENENEN

HHH 2.12.12.1

BBB 2.02.02.0

CCC 2.52.52.5

NNN 3.03.03.0

OOO 3.53.53.5

SSS 2.52.52.5

ClC lC l 3.03.03.0

PPP 2.12.12.1

SiS iS i 1.81.81.8

Practice Problems9.71. Infrared Spectroscopy.

Carbon dioxide is a linear molecule. The vibrations of the three

atoms include symmetrical stretching, bending, and

asymmetrical stretching, and their frequencies are

4.02X1013 s-1, 2.00X1013 s-1, and 7.05X1013 s-1, respectively.

(a) What region of electromagnetic spectrum corresponds to

these frequencies?

(b) Calculate the energy (in J) of each vibration. Which occures

most easily?

Practice Problems9.65.

During welding, a highly exothermic reaction of acetylene C2H2

and pure oxygen heats the metal pieces and fuses them.

Use Table 9.2 to find the heat of reaction per mole of acetylene

(with water formed as a gas)

(a) When 500.0 g of acetylene burns, how many kilojoules of

heat are given of?

(b) How many liter of O2 at 298 K and 18.0 atm are consumed?

C—H 413 kJ/mol

C # C 839 kJ/mol

O—H 467 kJ/mol

C=O 799 kJ/mol

Lewis electron-dot Structures Chemical Bonding, again B

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