bonding with chemistry lewis dot structures vsepr and molecular geometry
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Bonding with Chemistry
Lewis Dot Structures
VSEPR and Molecular Geometry
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A chemical bond is made by sharing electrons between two atoms to achieve the outer electron configuration of the noble gases.
Chemical Bonds
Ionic Covalent
Polar (dipole moment)
Nonpolar
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Each element has a preferred outer shell electron configuration.
An element tends to form enough bonds to achieve the number of electrons corresponding to the nearest noble gas.
This is a periodic (repeating) property of each column (family) of elements.
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So the number of outer shell electrons can be determined from the periodic table:
1 H
2 He
3 Li
4 Be
5 B
6 C
7 N
8 O
9 F
10Ne
11Na
12Mg
13Al
14Si
15P
16S
17Cl
18Ar
19K
20Ca
21Sc
22Ti
23V
24Cr
25Mn
26Fe
27Co
28Ni
29Cu
30Zn
31Ga
32Ge
33As
34Se
35Br
36Kr
37Rb
38Sr
39Y
40Zr
41Nb
42Mo
43Tc
44Ru
45Rh
46Pd
47Ag
48Cd
49In
50Sn
51Sb
52Te
53I
54Xe
55Cs
56Ba
57La**
72Hf
73Ta
74W
75Re
76Os
77Ir
78Pt
79Au
80Hg
81Tl
82Pb
83Bi
84Po
85At
86Rn
87Fr
88Ra
89Ac**
104Rf
105Ha
106Sg
107Ns
108Hs
109Mt
110 111 Etc.
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Lewis dot structures provide a simple means to determine bonding capacity:
Bonding requirements for achieving an octet of electrons in the outer orbital:
Element Bonds needed
C 4
N 3
P 3 or 5
O 2
S 2 or 6
F 1
Cl 1
Br 1
I 1
H 1
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VSEPR = valence shell electron pair repulsion theory indicates what molecular geometry we expect.
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Essential bonding characteristic of carbon atoms:
Carbon has 4 outer shell electrons.It needs 4 more to achieve the Neon
configuration of 1s22s22p6.It forms 4 bonds total.
Never forget this. It will help you a lot!!!
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Review:
How many bonds does hydrogen form? How many bonds does oxygen form? How many bonds does carbon form?
What is the molecular geometry of water? What is the molecular geometry of oxygen
gas? What is the molecular geometry of CH4?
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Organic chemistry
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We begin with Hydrocarbons
Hydrocarbons are composed of the elements __________ and __________, just like the name implies.
Three major classes of hydrocarbons Alkanes Alkenes Alkynes
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Speaking of alkanes, alkenes, alkynes, etc:
Every subject has its own language. Listen to military people talk and you know this is true!
Organic chemistry is positively loaded with new language to learn. Hang in there, it will come with time…
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Alkanesaka saturated hydrocarbons
StructureNames = nomenclatureProperties
PhysicalChemical
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We don’t have to stop at C10… for example, C20 is called eicosane. We’ll see that in a later chapter.
# Carbons Name1 methane2 ethane3 propane4 butane5 pentane6 hexane7 heptane8 octane9 nonane10 decane
Counting the organic way
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Melting and boiling points of alkanes
Straight Chain Alkanes: Melting Points (o C)
-182
-183
-188
-138 -1
30
-95
-91
-57
-54
-30 -26 -1
0 -5.5 6 10
18 22 28 32 36.8
-200
-150
-100
-50
0
50
0 5 10 15 20
Number of carbon atoms
Me
ltin
g p
oin
t (o
C)
Straight Chain Alkanes: Boiling points (o C)
-161
.5
-88.
6 -42.
1 -0.5 36
.1 68.7 98
.4 125.
7 174.
1
195.
9
216.
3
235.
5
253.
5
270.
5
287 30
3
316.
7
330
343
150.
8
-200
-100
0
100
200
300
400
0 5 10 15 20
Number of carbon atoms
Bo
ilin
g p
oin
t (o
C)
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Cycloalkanes
Structural featuresNomenclatureProperties: similar to noncyclic alkanes
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Alkenesaka unsaturated hydrocarbons
Structural featuresNomenclatureProperties
PhysicalChemical
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Melting and boiling points of alkenes
Alkenes: Melting points (o C)
-169
-185 -185
-139
-106
-165
-138 -140
-119
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 1 2 3 4 5 6 7 8
Number of carbon atoms
Mel
tin
g p
oin
t (o
C)
Alkenes: Boiling points (o C)
-151
-47
30
63
94
31
0.93.7
-6.3
-200
-150
-100
-50
0
50
100
150
0 1 2 3 4 5 6 7 8
Number of carbon atoms
Bo
ilin
g p
oin
t (o
C)
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Alkynesaka unsaturated hydrocarbons
Structural featuresNomenclatureProperties
PhysicalChemical
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More families of organic compounds:
When we introduce other atoms than carbon and
hydrogen into hydrocarbons, we call these
functional groups. They have their own special
names.
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Examples of functional groups:
C C OH
CH3
CH3
CH3
CH3
H3CH3C
CH3
OH
O
OH
Cl
Cl
Cl
O
OH
ibuprofen
O
H
11
12
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More examples of functional groups in molecules:
O
O
O
OH
OH
HO
O
O
O
N
HO
O
O
OH
erythromycin
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Review:
Chemical bonding re: carbon compounds How many bonds?
Three major classes of hydrocarbons 1. 2. 3.
Counting the organic way:
Recognizing functional groups
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Problems to practice on:
Chapter 11 & Chapter 12: check out the chapter problems sheet for recommended problems for practice.