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
1A
2A
3A
4A
5A
6A
7A
2
Li
Be
B
C
N
O
F
Ne
3
Na Mg
Al
Si
P
S
Cl
Ar
8A
1. Determine the number of valence electrons
2. Place one dot at a time on four sides.
Lewis electron-dot Structures
1A
2A
3A
4A
5A
6A
7A
2
Li
Be
B
C
N
O
F
Ne
3
Na Mg
Al
Si
P
S
Cl
Ar
8A
1. Determine the number of valence electrons
2. Place one dot at a time on four sides.
All correct:
O
O
O
Octet Rule
1A
2A
3A
4A
5A
6A
7A
2
Li
Be
B
C
N
O
F
Ne
3
Na Mg
Al
Si
P
S
Cl
Ar
8A
when elements form compounds they attain a filled outer
shell of eight electrons
(exceptions)
Ionic Bonding Model
See sample problem 9.1
4Na + O2 ! 2Na2O
3s
2s
3p
Na
Na
2s
3s
3p
2p
3s
3p
+
inner shell
2p
2s
2p
2-
+O
O
2s
Na
2p
3s
3p
3s
3p
Na+
inner shell
Ionic Bonding Model
See sample problem 9.1
4Na + O2 ! 2Na2O
3s
2s
3p
Na
Na
2s
3s
Na
3p
2p
+
inner shell
2p
2s
2p
2-
+O
O
2s
2p
Na+
inner shell
3s
3p
Ionic Bonding Model
See sample problem 9.1
4Na + O2 ! 2Na2O
3s
2s
3p
Na
Na
2s
3s
3p
2p
3s
3p
+
inner shell
2p
2s
2p
2-
+O
O
2s
Na
2p
3s
3p
Na+
inner shell
Na
+
2Na+ +
O
O
2-
Na
Lattice Energy: the Driving Force
LiF
Li + 1/2F2 ! LiF
Lattice Energy: the Driving Force
LiF
Li + 1/2F2 ! LiF
Li (g) ! Li+(g) + e- "H(IE) = 520 kJ
F (g) + e- ! F"H(EA) = -328 kJ
"Htotal = +192 kJ
Lattice Energy: the Driving Force
LiF
Li + 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
E
n
t
h
a
l
p
y
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
Born-Haber Cycle
E
n
t
h
a
l Li (g) + 1/2F (g)
2
p o
"H vapor= 161 kJ/mol
y
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
Born-Haber Cycle
E
n
t
h
a
Li (g) + F (g)
l Li (g) + 1/2F (g)
BE ("HoBE)=79.5 kJ/mol
2
p o
"H vapor= 161 kJ/mol
y
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
Born-Haber Cycle
Li+ (g) + F (g)
E
IE of Li ("Hof (Li+))
n
520.5 kJ/mol
t
h
a
Li (g) + F (g)
l Li (g) + 1/2F (g)
BE ("HoBE)=79.5 kJ/mol
2
p o
"H vapor= 161 kJ/mol
y
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
Born-Haber Cycle
Li+ (g) + F (g)
E
EA of F ["Hof (F-(g))]
o
+
IE of Li ("H f (Li ))
n
-328 kJ/mol
520.5
kJ/mol
t
Li+ (g) + F¯ (g)
h
a
Li (g) + F (g)
l Li (g) + 1/2F (g)
BE ("HoBE)=79.5 kJ/mol
2
p o
"H vapor= 161 kJ/mol
y
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
Born-Haber Cycle
Li+ (g) + F (g)
E
EA of F ["Hof (F-(g))]
o
+
IE of Li ("H f (Li ))
n
-328 kJ/mol
520.5
kJ/mol
t
Li+ (g) + F¯ (g)
h
a
Li (g) + F (g)
l Li (g) + 1/2F (g)
BE ("HoBE)=79.5 kJ/mol
2
"Holattice (LiF(s))
p o
"H vapor= 161 kJ/mol
y
-1050 kJ/mol
H
Li (s) + 1/2F2(g)
"Hoverall
"Hof=-617 kJ/mol
LiF (s)
The Covalent Bond
H
HH
+
H
H• + •H !
H:H
H
H
Lewis electron-dot structures
single bond, a shared pair of electrons
The Covalent Bond
H
HH
+
H
H
H
The Covalent Bond
H
+
H
E
N
E
R
G
Y
kJ/mol
74 pm, bond distance
432
kJ/mol
The Covalent Bond
bond length is proportional to atomic size
distance
Types of Bonds and Bond
Order
single bond: bond order 1
H
+
+
Br
shared electrons
double bond: bond order 2
O
H
H Br
Br
O
triple bond: bond order 3
N + N
O
O
O
O
N
N
N
N
Types of Bonds and Bond
Order
H
H
C
H
O
C
H
O
Types of Bonds and Bond
Order
H
H
C
O
H
C
H
H
C
O
O
H
formaldehyde
Types of Bonds and Bond
Order
H
H
C
O
H
C
H
H
C
O
O
H
formaldehyde
H
O
H O
H
O
HO-
hydroxide anion
Types of Bonds and Bond
Order
NH2
O
O
N
H
O
C
C
C
N
O
P
O
P
O
O
P
O
O
CH2
C
O
H
H
C
N
O
C
C
N
C
H
H
C H
OH OH
adenosine triphosphate, ATP
which atoms have an unshared pair of electrons, and how many?
Types of Bonds and Bond
Order
NH2
O
O
N
H
O
C
C
C
N
O
P
O
P
O
O
P
O
O
CH2
O
C
O
H
"Hrxn = -31 kJ/mol
H2O
O
O
C
N
C
C
H
C
N
C H
H
H
OH OH
NH2
N
H C
C
C
N
O
O
O
O
P
O
P
O
P
O
CH2
H
OH
O
C
O
H
N
N
C
C
C H
OH OH
C
H
C
H
Bond Energy
A—B ! A• + •B
"Hrxn= bond energy
in gas phase
Bond Length and Energy
bond length
pm
bond energy
kJ/mol
C—F
133
C—F
453
C—Cl
177
C—Cl
339
C—Br
194
C—Br
276
C—I
213
C—I
216
Bond Length and Energy
bond length
pm
bond energy
kJ/mol
H—F
92
H—F
565
H—O
96
H—O
467
H—N
101
H—N
391
H—C
109
H—C
413
Bond Length and Energy
bond length
pm
bond energy
kJ/mol
C—C
154
347
C=C
134
614
C# C
121
839
Electronegativity
Electronegativity
Electronegativity
Electronegativity,
introduced by Pauling,
ranges from 0 to 4
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
electronegativity
As
S
H
Si
2.0
2.5
2.1
1.8
As2S3
SiH4
silane
more electronegative element will have the “negative sign”
O.N. and Electronegativity
+3 -2
electronegativity
As
S
H
Si
2.0
2.5
2.1
1.8
As2S3
SiH4
silane
more electronegative element will have the “negative sign”
O.N. and Electronegativity
+3 -2
electronegativity
As
S
H
Si
2.0
2.5
2.1
1.8
As2S3
+4 -1
SiH4
silane
more electronegative element will have the “negative sign”
Bond Polarity
H
!+
H
F
!F
Bond Polarity
!+
H
!N
!+
!+
H
H
ammonia
H
H
N
H
Bond Polarity
generally, bond polarity is proportional to "EN
polarity decreases
H—F
"EN 1.9
H—Cl
"EN 0.9
H—Br
"EN 0.7
H —I
"EN 0.1
Bond Polarity
generally, bond polarity is proportional to "EN
polarity decreases
H—F
"EN 1.9
H—O—H
"EN 1.4
NH3
"EN 0.9
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
Valence electrons
core
electrons
nuclei
metallic
bond
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)
H
C
H
O
H
C
H
H
O
C
O
H
pay attention to the unshared pairs of electrons
Key Concepts in Chapter 9
! Bonding: Ionic, Covalent, and Metallic
Born-Haber cycle and lattice energy
effects of ionic size and charge
Polar and Non-polar covalent bonds
trends in bond length and strength
and polarity
bond order: single, double and triple
bonds
Key Concepts in Chapter 9
! Electronegativity
relative ability of a bonded atom to attract
the shared electrons
F
F
"EN = 0
non-polar
Br
F
"EN = 1.2
polar
H
F
"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 Problems
9.67. 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 "Hof 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 Problems
9.52. 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 Problems
9.58. 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.
EN
H
2.1
(a) HBr, HCl, HI
B
2.0
C
2.5
(b) H2O, CH4, HF
N
3.0
O
3.5
(c) SCl2, PCl3, SiCl4
S
2.5
Cl
3.0
P
2.1
Si
1.8
Practice Problems
9.71. 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 Problems
9.65.
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
O—H
C=O
839 kJ/mol
467 kJ/mol
799 kJ/mol