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Bio100 Lecture2

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Table 2.1
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Figure 2.10
Name and
Molecular
Formula
Electron
Distribution
Diagram
(a) Hydrogen (H2)
H
H
(b) Oxygen (O2)
O
O
(c) Water (H2O)
H
O
H
(d) Methane (CH4)
H
H
C
H
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H
Lewis Dot
Structure and
Structural
Formula
SpaceFilling
Model
Figure 4.4
Hydrogen
(valence = 1)
Oxygen
(valence = 2)
Nitrogen
(valence = 3)
Carbon
(valence = 4)
H
O
N
C
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Figure 2.11
δ−
δ−
O
δ+
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H
H
H2 O
δ+
Figure 2.12_1
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
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Figure 2.12_2
+
−
Na
Cl
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na+
Sodium ion
(a cation)
Cl−
Chloride ion
(an anion)
Sodium chloride (NaCl)
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Animation: Ionic Bonds
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Figure 2.13
Na+
Cl−
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Figure 2.14
δ–
δ+
δ–
Water (H2O)
δ+
δ–
Hydrogen bond
Ammonia (NH3)
δ+
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δ+
δ+
Figure 2.16
Carbon
Hydrogen
Natural
endorphin
Nitrogen
Sulfur
Oxygen
Morphine
(a) Structures of endorphin and morphine
Natural
endorphin
Brain cell
Morphine
Endorphin
receptors
(b) Binding to endorphin receptors
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Figure 3.2
δ+
δ+
Polar covalent bond
δ–
δ–
Region of partial
negative charge
δ+
δ+
δ–
δ–
δ+
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Hydrogen bond
δ+
δ–
Surface tension is a measure of how difficult it is to
break the surface of a liquid
Water has an unusually high surface tension due to
hydrogen bonding between the molecules at the
air-water interface and to the water below
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Figure 3.3
Evaporation pulls water upward.
H2O
Adhesion
Two types of
water-conducting
cells
Direction
of water
movement
Cohesion
300 µm
H2O
H2O
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Evaporative Cooling
Evaporation (or vaporization) is transformation of
a substance from liquid to gas
Heat of vaporization is the heat a liquid must
absorb for 1 g to be converted to gas
As a liquid evaporates, its remaining surface
cools, a process called evaporative cooling
Evaporative cooling of water helps stabilize
temperatures in organisms and bodies of
water
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Figure 3.6
Ice floats in liquid water because hydrogen bonds in ice are more “ordered,”
making ice less dense than water
Water reaches its greatest density at 4ºC
If ice sank, all bodies of water would eventually freeze solid, making life
impossible on Earth
Hydrogen bond
Ice:
Hydrogen bonds
are stable
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Liquid water:
Hydrogen bonds
break and re-form
Figure 3.8
–
Na+
+
–
+
CI–
–
+
–
–
CI–
+
–
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–
Na+
+
–
+
–
+
–
+
–
Hydrophilic and Hydrophobic
Substances
A hydrophilic substance is one that has an affinity for water
A hydrophobic substance is one that does not have an affinity for water
Oil molecules are hydrophobic because they have relatively nonpolar bonds
Hydrophobic molecules related to oils are the major ingredients of cell
membranes
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The pH Scale
The pH of a solution is defined by the negative logarithm of H+
concentration, written as
pH = –log [H+]
For a neutral aqueous solution, [H+] is 10–7, so
pH = –(–7) = 7
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Figure 3.11
pH Scale
0
Acidic
solution
Increasingly Acidic
[H+] > [OH–]
1
Neutral
Neutral
solution
Basic
solution
Increasingly Basic
[H+] < [OH–]
[H+] = [OH–]
2 Gastric juice (in stomach),
lemon juice
3 Vinegar, wine,
cola
4 Tomato juice
Beer
5 Black coffee
Rainwater
6 Urine
Saliva
7 Pure water
Human blood, tears
8 Seawater
Inside small intestine
9
10
Milk of magnesia
11
Household ammonia
12
Household
13 bleach
14
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Battery acid
Oven cleaner
Figure 3.UN04
0
Acidic –
[H ] > [OH ]
+
+
Acids donate H in
aqueous solutions.
Neutral –
+
[H ] = [OH ]
7
–
Basic –
+
[H ] < [OH ]
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Bases donate OH
+
or accept H in
aqueous solutions.
14
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