Topics for TodayTopics for TodayLewis Dot Structures IILewis Dot Structures II

Nonbonding electronsNonbonding electrons

ResonanceResonance

ElectronegativityElectronegativity

O OO

O OO[

[

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[

[

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”

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

Topics for TodayTopics for TodayLewis Dot Structures IILewis Dot Structures II

Nonbonding electronsNonbonding electrons

ResonanceResonance

ElectronegativityElectronegativity

O OO

O OO[

[

Handout B!

Non-Bonding Electrons

What are What are non-bondingnon-bonding electrons? electrons?

What are What are non-bondingnon-bonding electrons? electrons?

Valence electrons that do not partake in bonding. Easy

enough….

Valence ElectronsValence Electrons

C N :O :Cl.... .

.. .. ..... ..

..

4 5 6 7 Valence Electrons

4 3 2 1 # of bonds

Review

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!!

How many nonbonding

electrons are in methane, ammonia,

water, and HCl?

C.... How many

bonds will form?

REVIEW

C HH

H

H

Methane, CH4

4 bonds around C (8 electrons)

REVIEW

•• N N •• How many bonds are likely to

form?

Ammonia, NHAmmonia, NH33

HH

H

N

3 bonds around N

Note the nonbonding

pair.

O O

How many bonds?

WaterWater

O — H

H

2 bonds around O

How many nonbondin

g pairs?

Cl Cl

How many bonds is Cl likely to

form?

Hydrogen chlorideHydrogen chloride

H — ClH — Cl

1 bond from Cl 1 bond from Cl

How many nonbondin

g pairs?

What happens to CFCs when they

get into the atmosphere?

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!

CCl2F2

λ < 220 nm

UV-C light

.CClF2 + Cl.

Where in the atmosphere

does this take place?

http://www.windows.ucar.edu/earth/images/atmosphere_mural.jpg

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????

Be able to write the same thing for

OH. and OH-1

Which is more reactive?

Why?

ON YOUR OWN

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?

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

Be able to complete this

worksheet from all directions!

Handout C!(resonance

forms!)

Handout CHandout C

Be careful of Be careful of resonance resonance forms!forms!

ResonanceResonance

Sometimes just Sometimes just oneone Lewis structure cannot Lewis structure cannot completely describe the actual chemical completely describe the actual chemical structure…structure…

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!

Look at Handout C!

Resonance - EXAMPLE

AHEAD

O OO..

..

..

.... ..

Ozone, O3

How many valence

electrons?

Is this the only way we could write

this structure?

O OO

O OO..

..

..

.... ..

.......

. ....OR

They are both

equal!

Neither ONE is correct!

Resonance structures for OResonance structures for O33

O OO[ [

O OO..

..

..

.... ..

.......

. ....

No one resonance form actually

represents the true structure of ozone.

Actual structure for

ozone…

O OO

An average of the two

resonance structures

Compare with O2

O=O O=O

oxygenoxygen ozoneozone

O OO

Which bond is

stronger?

OO22 O + O O + O

λ< 242 nmλ< 242 nm

OO33 O O22 + O + O

λ< 320 nmλ< 320 nm

UV- C

UV- B

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!

BenzeneBenzene

CC66HH66

A A hydrocarbonhydrocarbon

How many valence

electrons?

Fig.10.04aFig.10.04a

Figure 10.4p. 438

Fig.10.04bFig.10.04b

Figure 10.4p. 438

Fig.10.04bFig.10.04b

Figure 10.4p. 438

Is there any other way to

draw this structure?

So, how do we usually draw

benzene?

How many bonds are

between each carbon?

Fig.10.04cFig.10.04c

Figure 10.4p. 438

What is ANOTHER way that

atoms can differ??

Their “greediness” for electrons.

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)

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

Electronegativity: Electronegativity: Increases to the right and up the periodic table! WHY?

(RANGES FROM 0 to 4)

Why do we worry about

electronegativity?

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!!!

COVALENT BONDS

NONPOLAR POLAR

TYPES OF BONDSTYPES OF BONDS

Electronegativity Difference

Low High

IONICPOLARNONPOLAR

COVALENT

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!

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”

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.

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!

C HH

H

H

: :. .

. .

The electrons are shared (relatively) equally by the two atoms