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CHAPTER 5CHEMICAL BONDING
CHEMISTRY – DACS 1232
LECTURER
IMRAN SYAKIR MOHAMAD │MOHD HAIZAL MOHD HUSIN │ NONA MERRY MERPATI MITAN
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Valence electrons are the outer shell electrons of an atom.The valence electrons are the electrons that participate inchemical bonding.
1A
1
ns1
2A
2
ns2
3A
3
ns2np1
4A
4
ns2np2
5A
5
ns2np3
6A
6
ns2np4
7A
7
ns2np5
Group
# of valence e-
e- configuration
3
4
Li
+
F
Li+
F
-
The Ionic Bond (Electrovalence)
1s22s1
1s22s22p5
1s2
1s22s22p6
[He]
[Ne]
Li
Li+ + e-
e- +
F
F
-
F
-
Li+ +
Li+
F
-
An Ionic bond is the electrostatic force that holds ions together
in an ionic compound
Ionic compound combine a Group IA & Group IIA metal with
a halogen or oxygen
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A covalent bond is a chemical bond in which two or moreelectrons are shared by two atoms. (Non metal & non metal)
Why should two atoms share electrons?
F
F
+
7e-
7e-
F
F
8e-
8e-
F
F
F
F
Lewis structure of F2
lone pairs
lone pairs
lone pairs
lone pairs
single covalent bond
single covalent bond
The Covalent Bond
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8e-
H
H
O
+
+
O
H
H
O
H
H
or
2e-
2e-
Lewis structure of water
Double bond – two 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 bond
triple bond
or
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Bond Type
BondLength
(pm)
C-C
154
CC
133
CC
120
C-N
143
CN
138
CN
116
Lengths of Covalent Bonds
Bond Lengths
Triple bond < Double Bond < Single Bond
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Comparison of Ionic and Covalent Compounds
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H
F
F
H
Polar covalent bond or polar bond is a covalent bond withgreater electron density around one of the two atoms
electron rich
region
electron poor
region
e- rich
e- poor
+
-
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Electronegativity is the ability of an atom to attract toward itselfthe electrons in a chemical bond.
Electron Affinity - measurable, Cl is highest
Electronegativity - relative, F is highest
Both are related butdifferent concepts. EArefers to an isolatedatom and E refers to anatom in chemical bond.Usually, EA > then E >.
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Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-
Increasing difference in electronegativity
Classification of bonds by difference in electronegativity
Difference
Bond Type
0
Covalent
2
Ionic
0 < and <2
Polar Covalent
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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.
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Intermolecular Forces
Intermolecular forces are attractive forces between molecules.
Intramolecular forces hold atoms together in a molecule.
Intermolecular vs Intramolecular
•41 kJ to vaporize 1 mole of water (inter)
•930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally,intermolecularforces are muchweaker thanintramolecularforces.
“Measure” of intermolecular force
boiling point
melting point
Hvap
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Intermolecular Forces
Dipole-Dipole Forces
Attractive forces between polar molecules
Orientation of Polar Molecules in a Solid
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Intermolecular Forces
Ion-Dipole Forces
Attractive forces between an ion and a polar molecule
Ion-Dipole Interaction
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Intermolecular Forces
Dispersion Forces (London)
Attractive forces that arise as a result of temporarydipoles induced in atoms or molecules
ion-induced dipole interaction
dipole-induced dipole interaction
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Intermolecular Forces
Dispersion Forces Continued
Polarizability is the ease with which the electron distributionin the atom or molecule can be distorted.
Polarizability increases with:
•greater number of electrons
•more diffuse electron cloud
Dispersionforces usuallyincrease withmolar mass.
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What type(s) of intermolecular forces exist betweeneach of the following molecules?
HBr
CH4
SO2
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Intermolecular Forces
Hydrogen Bond
The hydrogen bond is a special dipole-dipole interactionbetween they hydrogen atom in a polar N-H, O-H, or F-H bondand an electronegative O, N, or F atom.
A & B are N, O, or F
A H--B
A H--A
or
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Why is the hydrogen bond considered a “special”
dipole-dipole interaction?
Decreasing molar mass
Decreasing boiling point