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8/14/2019 Chapter 2 Notes Lecture
1/26
ChemistryOnline, 2009-2011
Chapter 2
Molecular Substance
and Lewis Structures
8/14/2019 Chapter 2 Notes Lecture
2/26
ChemistryOnline, 2009-2011
ANNOUNCEMENTS
HW#1: Chapter1: due (09/13/13)
HW#13.3 (Electron Config.), due:09/18/13
HW#2: Chapter 2: due (09/23/13)
HW#3: Chapter 3: due (09/23/13)
Exam#1: 09/23/13
(We will have it indifferent rooms)
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
A polyatomic ionis a group of atoms that are bonded
together by covalent bonds (a molecular compound)that has a net ionic charge. These combine with simple
ions to give more complex ionic compounds.
POLYATOMICIONS
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
Draw the Lewis structure for chlorate anion(ClO3-).
Cl OO
O
IN-CLASSPROBLEM
Draw the atoms and their
associated electrons.
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
5/26
ChemistryOnline, 2009-2011
Draw the Lewis structure for chlorate anion(ClO3-).
Cl OO
O
IN-CLASSPROBLEM
Draw the atoms and their
associated electrons.
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
6/26
ChemistryOnline, 2009-2011
IN-CLASSPROBLEM
Draw the atoms and their
associated electrons.
Next, add an extra electron
to the chlorine to give the
negative charge.
Draw the Lewis structure for chlorate anion(ClO3-).
Cl OO
O
8/14/2019 Chapter 2 Notes Lecture
7/26 ChemistryOnline, 2009-2011
Group the atoms and their
associated electrons so that
each oxygen has eight
electrons.
O Cl O
OThis also leaves eight electrons
around the chlorine.
IN-CLASSPROBLEM
Draw the Lewis structure for chlorate anion(ClO3-).
O Cl O
O
8/14/2019 Chapter 2 Notes Lecture
8/26 ChemistryOnline, 2009-2011
Draw the Lewis structure for nitrate anion(NO3-).
Draw the atoms and their
associated electrons.N OO
O
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
9/26 ChemistryOnline, 2009-2011
Draw the Lewis structure for nitrate anion(NO3-).
Draw the atoms and their
associated electrons.N OO
O
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
10/26
8/14/2019 Chapter 2 Notes Lecture
11/26 ChemistryOnline, 2009-2011
Draw the atoms and their
associated electrons. Next add an
extra electronto the nitrogen to
give the negative charge.
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
N OO
O
8/14/2019 Chapter 2 Notes Lecture
12/26 ChemistryOnline, 2009-2011
Group the atoms and their
associated electrons so that
each oxygen has eight
electrons.
O N O
O
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
This is not good, this is
not right, nitrogen only
has six electrons!
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
We can fix this, however, by simply
moving a pair of electrons from
one of the oxygens to form a
double bond to the nitrogen.
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
O N O
O
8/14/2019 Chapter 2 Notes Lecture
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8/14/2019 Chapter 2 Notes Lecture
15/26
ChemistryOnline, 2009-2011
This is a correct structure for
the nitrate anion...but is it
the only correct structure?
N OO
O
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
16/26
ChemistryOnline, 2009-2011
What if we had chosen to form
the double bond with the
oxygen on the left?
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
N OO
O
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ChemistryOnline, 2009-2011
How about the oxygen on the
bottom?N OO
O
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
So which one is correct?
All of them!
Draw the Lewis structure for nitrate anion(NO3-).
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
N OO
O
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
These structures are
called resonance forms
and because they differ
only in the arbi trary
placement of electrons,
they are all equivalent.
N OO
O
N OO
O
N OO
O
IN-CLASSPROBLEM
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
To indicate that they are resonance
forms, a special double headed
arrowis used to connect them. It
is important to note that theseforms do not represent distinct
structures, but that the nitrate
anion is a hybridof all of these
forms.
N OO
O
N OO
O
N OO
O
IN-CLASSPROBLEM
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
The hybrid looks something
like this.
N OO
O
N OO
O
N OO
O
N OO
O
IN-CLASSPROBLEM
8/14/2019 Chapter 2 Notes Lecture
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ChemistryOnline, 2009-2011
Nobody is perfect not even Lewis. As it turns out, the
octet ruleis a good guide, but there are manyexceptions. Many of these involve elements in the third
period and beyond
EXCEPTIONSTOTHEOCTETRULE
F
FF
F 120
0
S
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ChemistryOnline, 2009-2011
IN-CLASSPROBLEM
I VIII
II III IV V VI VII1
2
6
4
5
3
Draw the Lewis structure for sulfur tetrafluoride(SF4).
Draw the atoms and their
associated electrons so that
we can make four bonds.
S F
F
FF
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ChemistryOnline, 2009-2011
S F
F
FF
We seem to have a problem.
In order to form four bonds,
we must move one electron
pair on sulfur into storage
and then split the remaining
pair into single electrons.
IN-CLASSPROBLEM
Draw the Lewis structure for sulfur tetrafluoride(SF4).
Draw the atoms and their
associated electrons so that
we can make four bonds.
storage
S F
F
FF
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ChemistryOnline, 2009-2011
Finally, we must put our pair of
electrons back on the sulfur.
S F
F
FF
This gives the sulfur ten valence
electrons. This is called valence
expansion. Elements above the
second period may undergo
valence expansionif needed.
IN-CLASSPROBLEM
Draw the Lewis structure for sulfur tetrafluoride(SF4).
Now we can form fourbonds, giving the fluorines
eight electrons each.
8/14/2019 Chapter 2 Notes Lecture
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Ch i t O li 2009 2011
Group 4A Group 5A Group 6A Group 7A
S
F
F
F
F
Cl
F
F
F
Xe
F
F
P
F
F
F
F
F
Si
F
F
F
F
F
S
F
F
F
F
F
F
P
F
F
F
F
F
F
Si
F
F
F
F
F
F
2
Br
F
F
F
F
F
Xe
FF
F F
Group 8A
The table below shows several other examples of
valence expansion. These molecules and theirshapeswill be addressed further next semester.
EXCEPTIONSTOTHEOCTETRULE
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