The Basics of
Chemical Bonding
CHAPTER 9
Chemistry: The Molecular Nature of Matter, 6th edition
By Jesperson, Brady, & Hyslop
CHAPTER 9: Basics of Chemical Bonding
Learning Objectives
Communicate the difference between ionic and covalent bonding.
…
Predict which ionic compounds have relatively larger lattice energies
Predict ionic compounds
Use the Octet Rule
Familiarity with common covalent molecules: organic molecules
Draw lewis dot structures for covalent molecules
 Utilize multiple bonds
 Know the exceptions to the octet rule
 Predict electronegativity of a bond and overall dipole moment
 Recognize and create reasonable resonance structures for molecules
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2
Covalent Compounds
• Form individual separate molecules
– Atoms bound by sharing electrons
• Do not conduct electricity
• Often low melting point
Covalent Bonds
• Shared pairs of electrons between two
atoms
• Two H atoms come together, why?
3
Covalent
Bonds
Ionic vs Covalent Bonds
Ionic Bonds result from electrostatic attraction
between a cation and anion: metal-nonmetal (with the
exception of NH4+ and H3O+ cations).
Covalent bonds result from the sharing of electrons
between two atoms: nonmetal-nonmetal.
Li
F
Ionic Bonds
Covalent Bonds
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Molecular Nature of Matter, 6E
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Covalent Bond
• Attraction of valence electrons of one atom
by nucleus of other atom
• Shifting of electron density
• As distance between nuclei decreases,
probability of finding either electron near
either nucleus increases
• Pulls nuclei closer together
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Covalent Bond
• As nuclei get
close
– Begin to repel
each other
– Both have
high positive
charge
 Final internuclear distance between two atoms in
bond
 Balance of attractive and repulsive forces
 Bond forms since there is a net attraction
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Covalent Bond
• Two quantities characterize this bond
Bond Length (bond distance)
– Distance between 2 nuclei = rA + rB
Bond Energy
– Also bond strength
– Amount of energy released when bond formed
(decreasing PE) or
– Amount of energy must put in to “break” bond
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Lewis Structures
• Molecular formula drawn with Lewis Symbols
• Method for diagramming electronic structure
of covalent bonds
• Uses dots to represent electrons
• Covalent bond
– Shared pair of electrons
– Each atom shares electrons so has complete
octet ns 2np 6
• Noble gas electron configuration
• Except H which has complete shell with 2
electrons
8
Octet Rule:
When atoms form covalent bonds, they tend
to share sufficient electrons so as to achieve
outer shell having eight electrons
– Indicates how all atoms in molecule are
attached to one another
– Accounts for ALL valence electrons in ALL atoms
in molecule
Let’s look at some examples
Noble Gases: eight valence electrons
– Full octet ns 2np 6
– Stable monatomic gases
– Don’t form compounds
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Covalent
Bonds
Lewis Dot Structures
Diatomic Gases:
• H and Halogens
H2
• H· + ·H  H: H or H  H
• Each H has two electrons through sharing
• Can write shared pair of electrons as a line ()
: or  signify a covalent bond
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Lewis Dot Structures
Many nonmetals form more than one covalent bond
C
Needs 4 electrons
Forms 4 bonds
H
Needs 3 electrons
Forms 3 bonds
H N H
H C H
H
O
N
H
O H
H
H
H C H
H N H
H
H
methane
Needs 2 electrons
Forms 2 bonds
ammonia
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
O H
H
water
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Covalent
Bonds
Lewis Dot Structures: Multiple Bonds
Double Bond
Two atoms share two pairs of electrons e.g. CO2
O
C
O
O C O
O C O
Triple bond
Three pairs of electrons shared between two atoms e.g. N2
N
N
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
N
N
N
N
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Covalent
Bonds
Lewis Dot Structures
Diatomic Gases:
F2
F
+
F
FF
F
F
• Each F has complete octet
• Only need to form one bond to complete octet
• Pairs of electrons not included in covalent bond are called
lone pairs
• Same for rest of halogens: Cl2, Br2, I2
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Molecular Nature of Matter, 6E
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Covalent
Bonds
Lewis Dot Structures
Diatomic Gases:
HF
H + F
HF
H F
• Same for HCl, HBr, HI
• Molecules are diatomics of atoms that need only one
electron to complete octet
• Separate molecules
– Gas in most cases because very weak intermolecular
forces
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Lewis Dot Structures: Method
Step [1] Arrange the atoms next to each other that you
think are bonded together. Place H and
halogens on the periphery, since they can only
form one bond.
NH3
N
H
H
H
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Molecular Nature of Matter, 6E
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Covalent
Bonds
Step [2]
Lewis Dot Structures: Method
Count the valence electrons. The sum gives the
total number of e− that must be used in the Lewis
structure. For each atom the number of bonds =
8 – valence electrons.
Nitrogen has 5 valence electrons, so it will
have 8 – 5 = 3 bonds. Hydrogen will have
2-1 = 1 bond.
There are 8 total valance electrons
NH3
N
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
H
H
H
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Covalent
Bonds
Lewis Dot Structures: Method
Step [3] Arrange the electrons around the atoms.
Place one bond (two e−) between every two
atoms. Use all remaining electrons to fill
octets with lone pairs, beginning with atoms
on the periphery.
H
N
H
H
1 lone pair: 2
3 bonds:
6
Total e8
= total valence eJesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
1.
–
–
2.
3.
–
4.
5.
6.
–
–
Lewis Dot Structures: Method
Decide how atoms are bonded
Skeletal structure = arrangement of atoms.
Central atom
• Usually given first
• Usually least electronegative
Count all valence electrons (all atoms)
Place two electrons between each pair of atoms
Draw in single bonds
Complete octets of terminal atoms (atoms attached to central
atom) by adding electrons in pairs
Place any remaining electrons on central atom in pairs
If central atom does not have octet
Form double bonds
If necessary, form triple bonds
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Lewis Dot Structures: Ex: SiF4
Skeletal Structure
1 Si = 1 
= 4
4 F = 4  7e– = 28 e–
Total = 32 e–
single bonds – 8 e–
24 e–
F lone pairs – 24 e–
0 e–
4e–
F
e–
F
Si
F
F
Complete terminal atom
octets
F
F
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
Si
F
F
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Covalent
Bonds
Covalent Compounds: Organic Molecules
• Organic Molecules contain C-H bonds
• Carbon containing compouns
– Exist in large variety
– Mostly due to multiple ways in which C can form bonds
• Functional groups
– Groups of atoms with similar bonding
– Commonly seen in C compounds
• Molecules may contain more than one functional group
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Organic Molecules: Carbon
Alkanes
e.g.
CH4
methane
– Hydrocarbons
CH3CH3 ethane
– Only single bonds
CH3CH2CH3 propane
Isomers
– Same molecular formula
H
– Different physical properties
H C H
– Different connectivity (structure)
H
H
H H H H
H C C C H
H C C C C H
H H H
H H H H
butane
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
iso-butane
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Covalent
Bonds
Organic Molecules: Hydrocarbons
• Alkenes
– Contain at least one
double bond
H C C H
H H
ethylene
(ethene)
H H
H C C C C H
H H H H
• Alkynes
– Contain at least one
triple bond
H C C H
H H
butene
acetylene
(ethyne)
H C C C C H
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
H H
butyne
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Covalent
Bonds
Organic Molecules:
Oxygen Containing Organics
• Alcohols
– Replace H with OH
H
H H
H C O
H C C O
H H
H H H
methanol
• Ketones
– Replace CH2 with C=O
– Carbonyl group
Aldehydes
Ketones
Carboxylic acids
ethanol
H O H
H C C C H
H
H
acetone
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Organic Molecules:
Oxygen Containing Organics
H O
• Aldehydes
– At least one atom
attached to C=O is H
H C C H
H
acetaldehyde
• Organic Acids
– Contains carboxyl group
– COOH
H O
H C C O
H
H
acetic acid
Jesperson, Brady, Hyslop. Chemistry: The
Molecular Nature of Matter, 6E
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Covalent
Bonds
Organic Molecules:
Nitrogen Containing Organics
Amines
– Derivatives of NH3 with H’s replaced by alkyl groups
H H
H H H
H C N H
H C N C H
H
methylamine
H
H
dimethylamine
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Molecular Nature of Matter, 6E
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Problem
Set B
1. …..