Chapter 5
Chemical Bonding
The Covalent Bond
Covalent or Ionic ???
Electronegativity – the attraction that an
atom has for the electrons that it is sharing
w/ another atom
 Scale devised by Nobel Prize winner Linus
Pauling
 Based on scale with fluorine assigned 4.0,
the highest value

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Forming Chemical Bonds
• According to the Lewis model
– an atom may lose or gain enough electrons to
acquire a filled valence shell and become an ion.
An ionic bond is the result of the force of
attraction between a cation and an anion.
– an atom may share electrons with one or more
other atoms to acquire a filled valence shell. A
covalent bond is the result of the force of
attraction between two atoms that share one or
more pairs of electrons.
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Covalent Bonds
A chemical bond in which 2 atoms share a
single of electron to form one bond
 Examples F and H

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Covalent Bonds
Two nonmetal atoms form a covalent
bond because they have less energy
after they bonded
H +
H
H : H = HH = H2
hydrogen molecule
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Double Covalent Bond
2 pairs of electrons are shared between 2
atoms
Example O2


O


+

O




O::O


double bond
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Triple Covalent Bond
3 pairs of electrons are shared between 2
atoms
Example N2


N


+

N



N:::N

triple bond
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Diatomic Elements





Elements that are naturally in molecules with 2
atoms each.
HONClBrIF (pneumonic)
Existing as diatomic molecule yields a stable octet
Gases that exist as diatomic molecules are H2,
F2, N2, O2, Cl2, Br2, I2
Examples Fluorine & Bromine
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Learning Check
Use the name of the element to
name the following diatomic
molecules.
H2
hydrogen
N2
nitrogen
Cl2
_______________
O2
_______________
I2
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_______________
Solution
Use the name of the element to
name the following diatomic
molecules.
H2
hydrogen
N2
nitrogen
Cl2
chlorine
O2
oxygen
I2
iodine
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Lewis Structures
Other molecules having single covalent bonds
H 2O
The hydrogens share their electrons w/
oxygen so that O has 8 e- and each H has 2
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Covalent Bonds in NH3
Bonding pairs
H

H
:
N
:
H

Lone pair of electrons
(unshared pair)
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Drawing Lewis Structures
1. Determine the number of valence electrons in the
molecule
2. Decide on the arrangement of atoms in the
molecule
3. Connect the atoms by single bonds
4. Show bonding electrons as a single line; show
nonbonding electrons as a pair of Lewis dots
5. In a single bond, atoms share one pair of electrons;
in a double bond, they share two pairs, and in a
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Coordinate Covalent Bond
Bond in which only one atom donates
electrons to form the bond
 Sometimes an arrow is used to designate
the coordinate covalent bond

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Chemical Bonding:
The Covalent Bond Model
cont’d
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Chemical Bonding:
The Covalent Bond Model
cont’d
←
© Bettman/CORBIS
Fig. 5.10
Linus Pauling received
the Nobel Prize in
chemistry in 1954 for his
work on the nature of the
chemical bond.
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Electronegativity
 The attraction of an atom for electrons is
called its electronegativity.
 Fluorine has the greatest electronegativity.
 The metals have low electronegativities.
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Chemical Bonding:
The Covalent Bond Model
cont’d
→
Fig. 5.11
Abbreviated periodic
table showing Pauling
electronegativity
values for selected
representative
elements.
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Electronegativity
• Electronegativity: a measure an atom’s
attraction for the electrons it shares in a
chemical bond with another atom
– on the Pauling scale, fluorine, the most
electronegative element is assigned a value of
4.0, and all other elements are assigned values
relative to fluorine
El ectron egati vity incre ases
-
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Stoker
Bond Polarity: Nonpolar
Nonpolar covalent bond
 Electrons are shared between atoms with
the same electronegativity values.
 Difference = 0
 Examples:
N2
Br2
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Bond Polarity: Polar
Polar covalent bond
 Electrons are shared between different
nonmetal atoms Examples:
O-Cl
O-S
N-Cl
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Chemical Bonding:
The Covalent Bond Model
←
Fig. 5.12
(a) In the nonpolar
covalent bond present,
there is a symmetrical
distribution of electron
density. (b) In the polar
covalent bond present,
electron density is
displaced because of its
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Chemical Bonding:
The Covalent Bond Model
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Learning Check
Identify the type of bond between the
following atoms
A. K-N
1) nonpolar
2) polar
3) ionic
B. N-O
1) nonpolar
2) polar
3) ionic
C. Cl-Cl
1) nonpolar 2) polar
3) ionic
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Solution
A. K-N
3) ionic
B. N-O
2) polar, covalent
C. Cl-Cl
1) nonpolar, covalent
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Covalent or Ionic ???

To decide whether a bond is covalent or
ionic find the difference in electronegativities
< 2.0 covalent
> 2.0 ionic
Try KF, MgS, Cl2
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Character of Bonds
Chemist find it better to express chemical
bonds as % ionic and % covalent
 Relates electronegativity to ionic and
covalent percentages
 Table 7.2 (p 159) in text

Try KF, MgS, Cl2
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Molecular Polarity
Just like bonds molecules can have polarity
 Look at

Molecule geometry atoms (how atoms are
arranged in space)
 Bond polarity

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Chemical Bonding:
The Covalent Bond Model
Fig. 5.13
(a) Methane is a
nonpolar tetrahedral
molecule. (b) Methyl
chloride is a polar
tetrahedral molecule.
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Electronegativity
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Writing Formulas
Nonmetal/Nonmetal
 In covalent bonds, the element with the
lowest electronegativity is written first
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Chemical Bonding:
The Covalent Bond Model
→
Table 5.1
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Chemical Bonding:
The Covalent Bond Model
→
Table 5.2
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Naming of 2 Nonmetals
Name each element
2. End the last element in –ide
3. Add prefixes to show more than 1 atom
Prefixes
mon
1
hexa
6
di
2
hepta
7
tri
3
octa
8
tetra
4
nona
9
pent
5
deca
10
1.
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Learning Check
Fill in the blanks to complete the following
names of covalent compounds.
© Karen Timberlake
CO
carbon ______oxide
CO2
carbon _______________
PCl3
phosphorus _______chloride
CCl4
carbon ________chloride
N2O
_____nitrogen _____oxide
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Solution
© Karen Timberlake
CO
carbon monoxide
CO2
carbon dioxide
PCl3
phosphorus trichloride
CCl4
carbon tetrachloride
N2O
dinitrogen monoxide
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Learning Check
A.
B.
C.
P2O5
Cl2O7
Cl2
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Solution
© Karen Timberlake
A.
P2O5
diphosphorus pentoxide
B.
Cl2O7
dichlorine heptoxide
C.
Cl2
chlorine
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Learning Check
• Examples
– draw a Lewis structure for hydrogen
peroxide, H2O2
– draw a Lewis structure for methanol,
CH3OH
– draw a Lewis structure for acetic acid,
CH3COOH
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Lewis Structures
O
H
H N H
H
H 2O (8)
Water
H
H
NH 3 (8)
Ammonia
H
C C
H
H C H
H
CH 4 (8)
Methane
H Cl
HCl (8)
Hydrogen chloride
O
H
H C C H
C
O
H
H
C2 H 4 (12)
C2 H 2 (10)
H
CH 2O (12)
Ethylene
Acetylene
Formaldehyde
H
C
H
O
O
H 2CO 3 (24)
Carbonic acid
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3-D Characteristics of
Molecules


Atoms and molecules have 3 dimensions
Shapes of molecules lead to additional properties
of covalent compounds

Polar covalent Bonding



When electrons are not shared equally between two atoms
Bond that is certain % ionic
Nonpolar covalent Bonding


Electrons are shared equally
Diatomic atoms
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More Electron Pairs
Electron Angle
Pairs
4
109°
Bonded Name of
Atoms Shape
4
tetrahedral
4
109°
3
pyramidal
4
109°
2
bent, angular
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Shapes of Molecules
Number of electron pairs
(= negative charge clouds)
Number of bonded atoms
Angle
180°
Name of shape
2
2
linear
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Electron Shape with 3 Pairs
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SO2
S has 2 bonded atoms , 1 lone pair (electron cloud)
120°, angular
.. .. ..
:O:: S:O:
..
S
O
O
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