topics for today lewis dot structures ii nonbonding electrons resonanceelectronegativity oo o oo o [...
TRANSCRIPT
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Topics for TodayTopics for TodayLewis Dot Structures IILewis Dot Structures II
Nonbonding electronsNonbonding electrons
ResonanceResonance
ElectronegativityElectronegativity
O OO
O OO[
[
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Readings for Today (Review)Readings for Today (Review)
Atomic Structure and Periodicity Atomic Structure and Periodicity Section 2.2Section 2.2What’s in a bond? Seeing Electrons What’s in a bond? Seeing Electrons Section 2.3Section 2.3
O OO
O OO[
[
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Topics for WednesdayTopics for Wednesday
CFCs and the Ozone HoleCFCs and the Ozone HoleThe ClThe Cl.. Radical RadicalProperties and Uses of CFCs!Properties and Uses of CFCs!
“We’ve got Styrofoam boxes
for the ozone layer”
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Readings for WednesdayReadings for Wednesday
Review 2.9 CFCs: Properties, uses and Review 2.9 CFCs: Properties, uses and interactions with ozone interactions with ozone
2.11 Responses to a global concern2.11 Responses to a global concern
2.12 Looking to the future2.12 Looking to the future
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Topics for TodayTopics for TodayLewis Dot Structures IILewis Dot Structures II
Nonbonding electronsNonbonding electrons
ResonanceResonance
ElectronegativityElectronegativity
O OO
O OO[
[
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Handout B!
Non-Bonding Electrons
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What are What are non-bondingnon-bonding electrons? electrons?
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What are What are non-bondingnon-bonding electrons? electrons?
Valence electrons that do not partake in bonding. Easy
enough….
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Valence ElectronsValence Electrons
C N :O :Cl.... .
.. .. ..... ..
..
4 5 6 7 Valence Electrons
4 3 2 1 # of bonds
Review
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Drawing Lewis Dot Structures!!Drawing Lewis Dot Structures!!
1) MEMORIZE the # valence electrons for C, H, O, N, Cl
and related elements!
2) KNOW the octet (or duet)
rule!!
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How many nonbonding
electrons are in methane, ammonia,
water, and HCl?
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C.... How many
bonds will form?
REVIEW
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C HH
H
H
Methane, CH4
4 bonds around C (8 electrons)
REVIEW
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•• N N •• How many bonds are likely to
form?
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Ammonia, NHAmmonia, NH33
HH
H
N
3 bonds around N
Note the nonbonding
pair.
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O O
How many bonds?
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WaterWater
O — H
H
2 bonds around O
How many nonbondin
g pairs?
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Cl Cl
How many bonds is Cl likely to
form?
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Hydrogen chlorideHydrogen chloride
H — ClH — Cl
1 bond from Cl 1 bond from Cl
How many nonbondin
g pairs?
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What happens to CFCs when they
get into the atmosphere?
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FREON-12 (dichlorodifluoromethane)
C
Cl
Cl
F
F
UV-C
What does UV light
usually do to bonds?
CCl
F
F.
+ Cl.
Don’t forget about the
nonbonding electrons!
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CCl2F2
λ < 220 nm
UV-C light
.CClF2 + Cl.
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Where in the atmosphere
does this take place?
http://www.windows.ucar.edu/earth/images/atmosphere_mural.jpg
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What is the difference
between Cl. And Cl-?
Cl. Cl-
Chlorine radical Chloride ion
Draw the Lewis
structure for each!
What do we do with the charge?
:Cl....
. :Cl:....
-
Which one is more
reactive?
Why????
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Be able to write the same thing for
OH. and OH-1
Which is more reactive?
Why?
ON YOUR OWN
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Write the complete reaction for the ionization Write the complete reaction for the ionization of Hof H22O in Lewis structure form!!O in Lewis structure form!!
H2O vs H2O.+
Don’t forget the
nonbonding electrons!
ON YOUR OWN
Which is more reactive?
Why?
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Why do CO and NWhy do CO and N22 look the same? look the same?
1. Count the
valence electrons
2. Follow
the octet rule!
ON YOUR OWN
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Be able to complete this
worksheet from all directions!
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Handout C!(resonance
forms!)
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Handout CHandout C
Be careful of Be careful of resonance resonance forms!forms!
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ResonanceResonance
Sometimes just Sometimes just oneone Lewis structure cannot Lewis structure cannot completely describe the actual chemical completely describe the actual chemical structure…structure…
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Sometimes Sometimes oneone Lewis structure cannot Lewis structure cannot completely describe the structure…completely describe the structure…
Resonance structures will always involve
a double bond!
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Look at Handout C!
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Resonance - EXAMPLE
AHEAD
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O OO..
..
..
.... ..
Ozone, O3
How many valence
electrons?
Is this the only way we could write
this structure?
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O OO
O OO..
..
..
.... ..
.......
. ....OR
They are both
equal!
Neither ONE is correct!
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Resonance structures for OResonance structures for O33
O OO[ [
O OO..
..
..
.... ..
.......
. ....
No one resonance form actually
represents the true structure of ozone.
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Actual structure for
ozone…
O OO
An average of the two
resonance structures
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Compare with O2
O=O O=O
oxygenoxygen ozoneozone
O OO
Which bond is
stronger?
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OO22 O + O O + O
λ< 242 nmλ< 242 nm
OO33 O O22 + O + O
λ< 320 nmλ< 320 nm
UV- C
UV- B
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Try the rest of the worksheet on your own!
HINT: SO2 will look a lot like
ozone… WHY?
HINT: Don’t forget the charge on
nitrate!
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BenzeneBenzene
CC66HH66
A A hydrocarbonhydrocarbon
How many valence
electrons?
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Fig.10.04aFig.10.04a
Figure 10.4p. 438
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Fig.10.04bFig.10.04b
Figure 10.4p. 438
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Fig.10.04bFig.10.04b
Figure 10.4p. 438
Is there any other way to
draw this structure?
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So, how do we usually draw
benzene?
How many bonds are
between each carbon?
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Fig.10.04cFig.10.04c
Figure 10.4p. 438
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What is ANOTHER way that
atoms can differ??
Their “greediness” for electrons.
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Electronegativity Electronegativity – the measure of an atom’s – the measure of an atom’s attraction for electrons in a chemical bond attraction for electrons in a chemical bond (CiC)!(CiC)!
Every element has its own
electronegativity!
(RANGES FROM 0 to 4)
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2.1
1.0
0.9
0.8
1.2
1.0
3.0 3.52.5 4.0
2.5 3.0
2.8
2.5
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Electronegativity: Electronegativity: Increases to the right and up the periodic table! WHY?
(RANGES FROM 0 to 4)
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Why do we worry about
electronegativity?
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Covalent BondsCovalent Bonds
O=C=O
C HH
H
H
C HH
H
H
: :. .
. .
O:: OC::
A bond where two atoms share electrons
..
.. ....
methane, CH4
carbon dioxide, CO2
Not all covalent bonds are
created equal!!!
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COVALENT BONDS
NONPOLAR POLAR
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TYPES OF BONDSTYPES OF BONDS
Electronegativity Difference
Low High
IONICPOLARNONPOLAR
COVALENT
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Polar Bonds: Polar Bonds: Unequal sharingUnequal sharing of electrons of electrons in a chemical bond. Still a in a chemical bond. Still a covalentcovalent bond! bond!
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H ClEN
H
Cl
2.1
3.0
High difference
in EN!
Cl pulls the electrons
towards it!
δ-δ+
Read as “delta minus”
Means “slightly negative”
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H H —— Cl or H Cl or H ::ClCl
Unequal sharingUnequal sharing of 2 electrons by 2 of 2 electrons by 2 atoms. The bond in HCl is a atoms. The bond in HCl is a polar polar bond.bond.
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H Cl
C HH
H
H
EN
H
Cl
C
2.1
2.5
3.0
High difference
in EN!HCl is a
polar bond!
δ-δ+
What about
methane?
The C-H bond is
nonpolar!
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C HH
H
H
: :. .
. .
The electrons are shared (relatively) equally by the two atoms