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When Atoms Meet
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Bonding Forces
Electronelectron
repulsive forces
Nucleusnucleus
repulsive forces
Electronnucleus
attractive forces
Bonds
Forces that hold groups of atoms
together and make them function as a
unit.
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Metals and Nonmetals
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Types of Chemical Bonding
1. Metal with nonmetal:
electron transfer and ionic bo nding
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Three models of chemical bonding
Electron transfer
Ionic
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Types of Chemical Bonding
1. Metal with nonmetal:
electron transfer and ionic bo nding
2. Nonmetal with nonmetal:
electron shar ing and covalent b onding
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Three models of chemical bonding
Electron transfer Electron sharing
Ionic Covalent
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Types of Chemical Bonding
1. Metal with nonmetal:
electron transfer and ionic bo nding
2. Nonmetal with nonmetal:
electron shar ing and covalent b onding
3. Metal with metal:
electron pool ing and metal l ic bo nding
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Three models of chemical bonding
Electron transfer Electron sharing Electron pooling
Ionic Covalent Metallic
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The outer shell electrons of an atom
Participate in chemical bonding
1A 1ns1
2A 2ns2
3A 3ns2np1
4A 4ns2np2
5A 5ns2np3
6A 6ns2np4
7A 7ns2np5
Group # of valence e-e-configuration
Valence Electrons
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G. N. Lewis
Developed the idea in1902.
Lewis Structures
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Nitrogen, N, is in Group 5A and therefore has 5 valence
electrons.
N:
.
..
:
N .. .
.N :.
.:
N ...
Place one dot per valence electron on each of the four
sides of the element symbol.
Pair the dots (electrons) until all of the valence electrons are
used.
Lewis Dot Symbols
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Lewis Dot Symbols
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The OctetRule
Chemical compounds tend to form so that each
atom, by gaining, losing, or sharing electrons, haseightelectrons in its highest occupied energy
level.
The same number of electrons as in the nearestnoble gas
The first exception to this is hydrogen, which
follows the duet rule.The second exception is helium which does not
form bonds because it is already full with its
two electrons
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Li + F Li+ F -
Ionic Bond
1s22s11s22s22p5 1s21s22s22p6[He][Ne]
Li1s 2s 2p
F
1s 2s 2p
+
Li+
1s 2s 2p
F-
1s 2s 2p
+
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Lattice energy (E) increases
as Q increases and/oras r decreases.
cmpd lattice energy
MgF2
MgO
LiF
LiCl
2957
3938
1036
853
Q= +2,-1
Q= +2,-2
r F< r Cl
Electrostatic (Lattice) Energy
E = kQ+Q-
r
Q+is the charge on the cation
Q-is the charge on the anion
r is the distance between the ions
Latt ice energy(E) is the energy required to completely separate
one mole of a solid ionic compound into gaseous ions.
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A chemical bond in which two or more electrons are shared by
two atoms.
How should two atoms share electrons?
F F+
7e- 7e-
F F
8e- 8e-
F F
F F
Lewis structure of F2
lonepairslonepairs
lonepairslonepairs
single covalent bond
single covalent bond
Covalent Bond
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Distribution of electron density of H2
H H
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8e-
H HO+ + OH H O HHor
2e- 2e-
Lewis structure of water
Double bondtwo atoms share two pairs of electrons
single covalent bonds
O C O or O C O
8e- 8e-8e-double bonds double bonds
Triple bond
two atoms share three pairs of electrons
N N
8e-8e-
N N
triple bondtriple bond
or
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H F FH
A covalent bond with greater electron density around
one of the two atoms
electron rich
regionelectron poor
region e-riche-poor
d+ d-
Polar Covalent Bond
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Electron density distributions in
H2, F2, and HF.
El t ti iti (EN)
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Electronegativities (EN)
The ability of an atom in a molecule to attract shared electrons to itself
Linus Pauling
1901 - 1994
Cl ifi ti f B d
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Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-
Increasing difference in electronegativity
Classification of Bonds
Difference in EN Bond Type
0 Covalent2 Ionic
0 < and
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Classify the following bonds as ionic, polar covalent,
or covalent: The bond in CsCl; the bond in H2S; and
the NN bond in H2NNH2.
Cs 0.7 Cl 3.0 3.0 0.7 = 2.3 Ionic
H 2.1 S 2.5 2.5 2.1 = 0.4 Polar Covalent
N 3.0 N 3.0 3.0 3.0 = 0 Covalent
Classification of Bonds
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1. Draw skeletal structure of compound showing what
atoms are bonded to each other. Put leastelectronegative element in the center.
2. Count total number of valence e-. Add 1 for each
negative charge. Subtract 1 for each positive
charge.
3. Use one pair of electrons to form a bond (a single
line) between each pair of atoms.
4. Arrange the remaining electrons to satisfy an octetfor all atoms (duet for H), starting from outer atoms.
5. If a central atom does not have an octet, move in
lone pairs to form double or triple bonds on the
central atom as needed.
Rules for Writing Lewis Structures
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Write the Lewis structure of nitrogen trifluoride (NF3).
Step 1 N is less electronegative than F, put N in center
F N F
F
Step 2
Count valence electrons N - 5 (2s2
2p3
) and F - 7 (2s2
2p5
)5 + (3 x 7) = 26 valence electrons
Step 3 Draw single bonds between N and F atoms.
Step 4 Arrange remaining 20 electrons to complete octets
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Write the Lewis structure of the carbonate ion (CO32-).
Step 1 C is less electronegative than O, put C in center
O C O
O
Step 2
Count valence electrons C - 4 (2s2
2p2
) and O - 6 (2s2
2p4
)-2 charge 2e-
4 + (3 x 6) + 2 = 24 valence electrons
Step 3 Draw single bonds between C and O atoms
Step 4 - Arrange remaining 18 electrons to complete octets
Step 5 The central C has only 6 electrons. Form a double bond.
2-
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More than one valid Lewis structures can be written for a
particular molecule
The actual structure of the carbonate ion is an average of the
three resonance structures
O C O
O
- -O C O
O
-
-
OCO
O
-
-
Resonance
2- 2- 2-
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Exceptions to the Octet Rule
The Incomplete Octet
H HBeBe 2e-
2H 2x1e-
4e-
BeH2
BF3
B 3e-
3F 3x7e-24e-
F B F
F
3 single bonds (3x2) = 6
9 lone pairs (9x2) = 18Total = 24
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Exceptions to the Octet Rule
Odd-Electron Molecules
N 5e-O 6e-
11e-
NO N O
The Expanded Octet (central atom with principal quantum number n > 2)
SF6S 6e-
6F 42e-
48e-S
F
F
F
F
F
F
6 single bonds (6x2) = 12
18 lone pairs (18x2) = 36
Total = 48
C l t B d L th
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Bond
Type
Bond
Length
(pm)
C-C 154
CC 133
C
C 120
C-N 143
C
N 138C
N 116
Covalent BondLengths
Bond Lengths
Triple bond < Double Bond < Single Bond
Covalent Bond Energy
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The energy required to break a particular bond in one mole of
gaseous molecules is the bond energy.
H2 (g) H (g)+ H (g) 436.4 kJ
Cl2 (g) Cl (g)+ Cl (g) 242.7 kJ
HCl(g) H (g)+ Cl (g) 431.9 kJ
O2 (g) O (g)+ O (g) 498.7 kJ O O
N2 (g)
N(g)
+ N(g)
941.4 kJ N N
Bond Energy
Bond Energies
Single bond < Double bond < Triple bond
Covalent BondEnergy
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Contoh : O C O
tot= 0
H2O HOH
CO2 Non polar
Polar
Molecular Shape
VSEPR
Valence Shell Electron-pair Repulsion
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Vibrational Modes of Water
Infrared light
Infrared Spectrum of Water
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Infrared Spectrum of Water
100015002000
Wavenumber (cm-1)
Absorbance
100020003000
Liquid
Gas
Reveal the interactions between molecules and their environments
Infrared Spectrum of Caffeine
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Infrared Spectrum of Caffeine
100020003000
Wavenumber (cm-1)
Absorbance
Identification of compounds
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Acknowledgment
Some images, animation, and material have been taken from the following sources:
Chemistry, Zumdahl, Steven S.; Zumdahl, Susan A.; Houghton Mifflin Co., 6th Ed., 2003;
supplements for the instructor
General Chemistry: The Essential Concepts, Chang, Raymon; McGraw-Hill Co. Inc., 4th
Ed., 2005; supplements for the instructor
Principles of General Chemistry, Silberberg, Martin; McGraw-Hill Co. Inc., 1st Ed., 2006;
supplements for the instructor
NIST WebBook: http://webbook.nist.gov/
http://www.lsbu.ac.uk/water/vibrat.html
http://en.wikipedia.org/wiki/Caffeine
http://www.wilsonhs.com/SCIENCE/CHEMISTRY/MRWILSON/Unit%204%20Chemical%2
0Bonding%20Powerpoint1.ppt