Topics for Today

1
Topics for Today

• Lewis Dot Structures I
• Quiz 5

H
H
. .


C
H
C
H
H
H
. .
H
H
2
Readings for Today

• Atomic Structure and Periodicity Section 2.2
• Whats in a bond? Seeing Electrons Section 2.3

H
H
. .


C
H
C
H
H
H
. .
H
H
3
Topics for Monday

• Lewis Dot Structures II

O
O
O
O
O
O
4
Readings for Monday (Review)

• Atomic Structure and Periodicity Section 2.2
• Whats in a bond? Seeing Electrons Section 2.3

H
H
. .


C
H
C
H
H
H
. .
H
H
5
Topics for Wednesday

• Back to CFCs and Cl.

Weve got Styrofoam boxes for the ozone layer
6
Review
From Friday,
7
PSCs
In the spring (October), the clouds melt and the
chemicals (like Cl.) are released.
8
Cl
C
F
Cl
F
Dichlorodifluoromethane
9
Where does the Cl. come from?
10
Topics for Today

• Lewis Dot Structures I
• Electron Pairs
• Single Bonds
• Double Bonds
• Quiz 5

H
H
. .


C
H
C
H
H
H
. .
H
H
11
How are atoms different from one another?
12
How are atoms different from one another?
13

• Protons
• Neutrons
• Electrons
• Physical Properties
• Chemical Properties
• Radioactive?

How are atoms different from one another?
14
Another way atoms are different
15
Another way atoms are different
The form different numbers of bonds!
What is a bond?
16
Every chemical bond has
Just like every rose has its thorn
TWO Electrons!
OCO
17
H
H
. .


C
H
C
H
H
H
. .
H
H
18
That is, the electrons that participate in
chemical reactions!
These are the VALENCE / OUTER / BONDING electrons
H
H
. .


C
H
C
H
H
H
. .
H
H
19
What types of bonds are there?
20
Ionic Bonds

• A bond where electrons are transferred, not shared

21
Ionic Bonds

• A bond where electrons are transferred, not shared

What do the charges mean?
NaCl
MgO
O2-
Mg2
Cl-
Na
Magnesium Ion
Oxide Ion
Sodium Ion
Chloride Ion
22
Ionic Bonds
What other types of bonds are there?
1 LESS electron than proton!
1 MORE electron than proton
NaCl
MgO
O2-
Mg2
Cl-
Na
Magnesium Ion
Oxide Ion
Sodium Ion
Chloride Ion
23
Covalent Bonds
A bond where two atoms share electrons
..
..
O
O
C
OCO
..
..
carbon dioxide, CO2
H
H
. .


C
H
C
H
H
H
. .
H
H
methane, CH4
24
How else do elements differ?
The number of valence (bonding) electrons!
25
Lets focus on these (for now)
26
C
N
O
Cl
How many valence (bonding) electrons?
27
Look at the periodic table!
28
4A
5A
6A
7A
Group
4
5
6
7
Valence Electrons
C
N
O
Cl
29
Valence Electrons
4
5
6
7
Valence Electrons
.
..
..
..
.
.
.
.
.
.
C
N
O
Cl
..
.
.
.
How many bonds do these atoms form?
30
Valence Electrons
4
5
6
7
Valence Electrons
.
..
..
..
.
.
.
.
.
.
C
N
O
Cl
..
.
.
.
These look like unpaired electrons
How many bonds do these atoms form?
31
Valence Electrons
4
5
6
7
Valence Electrons
.
..
..
..
.
.
.
.
.
.
C
N
O
Cl
..
.
.
.
The octet rule!
4
3
2
1
of bonds
8
8
8
8
32
Valence Electrons

• The octet rule.
• Atoms will usually react until they have EIGHT
  valence electrons.

Atoms can get eight electrons by sharing
(covalent) or stealing (ionic) electrons!
33
Important Exception!

• Hydrogen and helium are too small for 8
  electrons. They only need TWO electrons.

How many bonds does H form?
.
H
34
Handout!

• Part A
• Molecules
• (bonding electrons only)

35

• Drawing Lewis Dot Structures!!

2) KNOW the octet (or duet) rule!!
1) MEMORIZE the valence electrons for C, H, O,
N, Cl and related elements!
36
Lets work on the handout!
37
How many bonds around C?
H
C
H
H
H
Methane, CH4
4 bonds around C (8 electrons)
38
Structural Formula!
H
H
C
H
C
H
H
H
Chemical formula
Ethane, C2H6 CH3CH3
Condensed structural formula
39
Structural Formula!
H
H
C
C
H
H
Chemical formula
Ethene, C2H4 CH2CH2
Condensed structural formula
40
Double Bond When four valence electrons are
shared between two atoms.
H
H
C
C
H
H
Ethene, C2H4
41
C
H
H
C
Ethyne, C2H2
42
Be able to complete this worksheet from all
directions!
43
Handout B!
44

• N

How many bonds likely to form?
45
Ammonia
Note the nonbonding pair.
N
H
H
H
3 bonds around N
46

• O

How many bonds?

47
Water
O H H
2 bonds around O
48

• Cl

How many bonds is Cl likely to form?

49
Hydrogen chloride

• H Cl
• 1 bond from Cl

50

• One major exception to the rule!! CO, carbon
  monoxide

51
Carbon Monoxide, CO
C O
We will find out why next time!
A colorless, odorless, tasteless gas
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