Covalent Bonding
Skeleton Diagrams
Edward A. Mottel
Department of Chemistry
Rose-Hulman Institute of Technology
Only the noble gases have exactly the
correct number of electrons to fill
their outermost s and p orbitals.
All other atoms have to lose, gain or share
electrons to attain the stability
associated
with the noble gases.
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Atoms which gain or lose electrons are called ions.
An ionic bond is the electrostatic attraction
that holds ions together.
A covalent bond is the sharing of electrons
between two atoms.
Atoms share electrons to attain
the electronic configuration and stability
of a noble gas.
Each atom has a tendency to form a certain number
of bonds in stable, neutral compounds.
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Bonding Tendencies
Bonds
Kernal
diagram
Skeleton
diagram
H
1
H•
H-
Li
1
Li •
Li -
Be
2
• Be •
- Be -
B
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3
•
•B•
-B-
Bonding Tendencies
Bonds
Kernal
diagram
•
Skeleton
diagram
C
4
•C •
•
N
3
•N •
•
O
2
• O•
-O-
F
1
•• F •
F-
••
-C-
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••
•• ••
••
-N-
Skeleton Diagrams
 These
atoms are neutral in charge.
 Only outer shell (valence) electrons are
included.
 Each atom tends to form a specific number of
bonds when it forms a molecule.
 Often, an unique atom is at the center of the
structure.
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Skeleton Diagrams of Molecules
hydrogen
fluoride
carbon
dioxide
boron
nitride
beryllium
oxide
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H–F
O=C=O
BN
Be=O
– represents a single bond
between two atoms
= represents a double bond
(i.e., two bonds) between the
same two atoms
 represents a triple bond
(i.e., three bonds) between
the same two atoms
Skeleton
Skeleton diagrams
diagramsprovide
indicate
information
whichsome
atoms
are boundabout
together.
the strength of the bond.
Skeleton Diagrams of Molecules
H
H N H
ammonia
H-N-H bond angle
107°
H O H
water
H-O-H bond angle
104.5°
H
H C
methane
H-C-H bond angle
109.5°
H
H
H C H
formaldehyde
H-C-H bond angle
~120°
O
Skeleton diagrams do not indicate bond angles!
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Skeleton Diagrams of Molecules
Bond Order
Bond Energy
fluorine
gas
(difluorine)
F–F
1
155 kJ·mol–1
oxygen
gas
(dioxygen)
O=O
2
495 kJ·mol–1
nitrogen
gas
(dinitrogen)
NN
3
941 kJ·mol–1
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Which gas is the most reactive?
Pairs Activity
 A pair
of people will work on one problem:
• One person is responsible for writing all
the information.
• The other person is responsible for saying
what should be written.
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On a card or a piece of paper
 Write
each sequential step necessary to draw
a skeleton diagram.
 Number each step.
 Amend and update the list.
• Either person may do this.
Draw the skeleton diagram of acetic acid, CH3COOH
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Isomers
 An
isomer is a compound with the same
molecular formula, but different structure.
• The atoms are linked differently together.
Draw the skeleton diagram of an isomer of
acetic acid, CH3COOH
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Isomers of C2H4O2
H
H
H C C O H
H C C O H
H O
acetic acid
O H glycolaldehyde
H
H C O C H
methyl formate H
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O
Unstable Isomers of C2H4O2
H
H H
H C O
H C C O H
O
O C H
H
H H
H C C H
O O
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Small ring structures
(containing 3 or 4 atoms
in the ring) are either
unstable or very reactive
Sodium Acetate
 Acetic
acid reacts with sodium hydroxide to
form sodium acetate and water.
Draw the skeleton diagram of sodium acetate.
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Draw the skeleton diagrams for
 boric
acid, H3BO3
 aluminum hydroxide
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Compare the Structures of Boric Acid
H3BO
Al(OH)3
3 and Hydroxide
and
Aluminum
H
O
aluminum hydroxide
H O B O H
H
boric acid
O
Both have similar
skeleton diagrams,
but different
chemical properties.
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H O Al O H
Thetheir
Periodic
Compare
position onStaircase
the periodic table.
Separates Metals and Nonmetals
nonmetals
metals
Boron is a metalloid or semi-metal,
whereas aluminum is metallic.
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Compare
the bond
Structures
of Boric Acid
Which
might break
to show
each chemical
character?
and Aluminum
Hydroxide
H
O
Metal oxides
are basic
H O B O H
H
Nonmetal oxides
are acidic
O
H O Al O H
Both have amphoteric character.
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Skeleton Diagrams
 The
skeleton bonding approach works for
many molecules;
• however, it fails to explain the bonding in
some simple molecules and ions.
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Skeleton Diagrams
 What
is the skeleton diagram for
• carbon monoxide
• ammonium ion
• cyanide ion
 Which atom(s) in each structure breaks the
skeleton bonding rules?
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Skeleton Diagram Failures
C O
or
H +
C O
H +
H N H or H N H
H
C N
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H
or
C N
Types of Bonds Formed
Lighter members of a family
often form multiple bonds
N N
P
P
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O O
S S S S S
S S S
P
P
Heavier members favor
additional single bonds.
Heavier Members of a Family
tend to form single bonds
O
O
O C O
Si
Si
O
O
carbon dioxide
Si
O
silicon dioxide
quartz, glass, sand
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O
O
O
Si
Si
O
Bonding Theories
 Ionic
Model
 Skeleton Diagrams
• Identifies how atoms are linked together
• Fails to describe the bonding in ions and
+
certain molecules (e.g., CO, NH4 , CN–)
• Fails to explain the geometry of molecules
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