Transcript video slide - Indiana University

Chapter 2: The Chemical Context of Life
Chapter 3: Water and the Fitness of the Environment
Concepts
2.1 Matter consists of chemical elements in pure
form and in combinations
2.2 An element's properties depend on the
structure of its atoms
2.3 The properties of molecules depend on
chemical bonding between atoms
- Ionic Bonds
- Covalent Bonds - Nonpolar and Polar
- Hydrogen Bonds
2.4 Chemical reactions make and break bonds
PowerPoint TextEdit Art Slides for
3.1 The polarity of water molecules results in
Biology, Seventh Edition
hydrogen bonding
Neil Campbell and Jane Reece
3.2 Four emergent properties of water make
water an ideal substance for supporting life
3.3 Dissociation of water molecules leads to
acidic
and
basic
Copyright
© 2005
Pearsonconditions
Education, Inc. publishing as Benjamin Cummings
Figure 2.4 The properties of an element depend on the structure of its atoms
Anatomy of a Helium (42He) atom
Electron Cloud (2 electrons)
This should be review
for most of you; if it is
NOT, read Ch 2 and 3
carefully, or click for a
quick review: p1, p2, p3
Electrons (-) charge
Nucleus
Protons
(+) charge
Neutrons
(no charge)
# of Protons
= Element’s ‘identity’; Atomic Number
# of Electrons
= Equal to protons if an atom (uncharged)
# of Neutrons
= Often equal to number of protons;
Isotopes differ by numbers of neutrons: For Carbon,
12C = 99%, 13C and 14C (radioactive; unstable) = 1%
(Figure 2.6 A PET scan, a medical use for radioactive isotopes)
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Figure 2.8 Electrons determine the chemical reactivity of
an atom: Electron-shell diagrams of the first 18 elements
Hydrogen
1H
First
shell
Chemical reactivity depends mostly
on the number of valence
electrons (in outermost shell).
Atoms are most stable when their
outermost electron shell is filled with
8 electrons (or 2 for H and He),
known as the _________________
Lithium
3Li
Beryllium
4Be
Sodium
11Na
Magnesium
12Mg
Boron
3B
2
He
4.00
Atomic
Mass
(#p+ #n)
Carbon
6C
Nitrogen
7N
Silicon
14Si
Phosphorus
15P
Atomic number
(#p)
Helium
2He
Element symbol
Electron-shell
diagram
Oxygen
8O
Fluorine
9F
Neon
10Ne
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Second
shell
Aluminum
13Al
Third
shell
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Figure 2.13 What is an ionic bond?
The result = Each ion has
1
Na = 1 lone valence electron
Cl= 7 valence electrons
Na
Na
Sodium atom
(uncharged)
Cl
Cl
Chlorine atom
(uncharged)
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2
An ionic bond can form
between the oppositely charged ions.
+
–
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
Figure 2.2 The emergent properties of a compound
+
Sodium
Chloride
You, too, are built of compounds (proteins, lipids, carbohydrates)
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Sodium Chloride
Figure 2.11 What is a Covalent Bond?
Electron-shell
diagram
Hydrogen (H2)
(H =
H
valence electron)
H
Structural
formula
H
H
O
O
O
H
Space-filling
model
Hint: A solid line
between atoms
= covalent bond
Oxygen (O2)
(O =
valence electrons)
O
Water (H2O):
a very special
case - next slide!
O
valence electrons)
H
H
H
H
Methane (CH4)
(C =
O
H
C
H
H
H
C
H
H
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H
Non-polar covalent
Bonds (H2 , O2 , CH4)
= electrons shared
equally.
Figure 2.12 / 3.2 What is a Polar covalent bond?
Not all covalent bonds are shared equally!
Figure 3.2 The polar
covalent bonds ________
water molecules result in
hydrogen bonding
____________ molecules
Because O (8 protons) is more
electronegative than H (1
proton), shared electrons are
pulled more toward oxygen.
This results in a polar covalent
bond, creating a
partial __________ charge on
the oxygen and a
partial __________ charge on
the hydrogens.
–
+
–
+
Hydrogen
bonds
H
–
H
–
+
+
–
Q: Can you draw in the
polar covalent bonds?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fig 2-15: Hydrogen Bonding: Between molecules
Made possible via the __________________ of electrons (polar covalent bonds).
O and N are big, electronegative atoms compared to H, resulting in +/- charges.
Opposites attract, forming Hydrogen bonds BETWEEN molecules.
Electronegative
atoms

Hydrogen
bond
Hint: Any time you see a dashed line
connecting 2 molecules = think Hydrogen Bond
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemical reactions make and break chemical bonds
O
H
H
H
H
+
O
O
H
H
H
O
O2
2 H2
H
2 H2O
Reactants
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Products
Figure 3.4 WATER! Amazing Property I:
Transpirational Pull
Surface Tension
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Figure 3.5 Amazing Property II:
Ice
Hydrogen bonds are stable
Liquid water
Hydrogen bonds
constantly break and re-form
Brrr...
Amazing Property III:
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Figure 3.6 Amazing Property IV: water is an excellent solvent
Hydration of NaCl:
Salt dissolving in
water:
Partially (-)
interacts
with Na+
–
Na+
+
The collective ‘pull’
of hydrogen bonds
–
+
+
–
Partially (+)
interacts
with Cl-
–
Na+
+
Cl–
+
Cl –
–
+
+
–
+
–
–
–
–
See also:
Figure 3.7 Hydration
of Lysozyme, a
water-soluble protein
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Water can spontaneously break into ions: (H+ and OH-)
1 L of pure (degassed) water has 0.0000001 g of H+ ions (or 10-7 g/L) = 10-7 M
Expressing this in simpler terms, we can say that water has a pH of 7
(percent hydrogen ion concentration) ***
–
+
H
H
H
H
H
***Formula***
pH = -log [H+]
pH = -log [10-7]
pH =
TRY IT!
H
H
Hydronium
ion (H3O+)
(or H2O and H+)
In pure water: H+ = (10-7 M)
+
H
Hydroxide
ion (OH–)
OH–= (10-7 M )
pH 7 is considered neutral (equal concentrations).
Handout: Converting [H+] to pH
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Figure 3.8 The pH scale and pH values of some aqueous solutions
-Battery acid:
-Stomach acid:
-Vinegar:
0.1 M H+
0.01 M H+
0.001 M H+
Increasingly Acidic
[H+] > [OH–]
Acids are chemicals that add H+ to
a solution, raising the [H+] to 10-6,
or 10-4 or 10-2 ! (There is a 10-fold
difference between each number
on the scale at right.)
pH Scale
0
1
Battery acid
2 Digestive (stomach) juice, lemon juice
3
Vinegar, beer, wine, cola
4 Tomato juice
5 Black coffee Rainwater
6 Urine
-Ammonia
0.00000000001 M H+
*********************************
Buffers readily accept or donate
H+ or OH- ions, keeping pH
relatively stable.
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7 Pure water
8
Increasingly Basic
[H+] < [OH–]
Bases are chemicals that accept
H+ ions (or release OH- ions) into
solution
Neutral
[H+] = [OH–]
Human blood
Seawater
9
10
11
Milk of magnesia
Household ammonia
12
Household bleach
13
14
Oven cleaner
Objectives, Ch 2 (Atoms/Chemistry) and Ch 3 (Water)
1.
Compare the physical properties (mass and charge) and the locations
of electrons, protons, and neutrons.
2.
Define the terms electron orbital and electron shell. Relate electron
shells to principle energy levels.
3.
Explain how the number of valence electrons of an atom is related to
its chemical properties.
4.
Distinguish among covalent bonds, hydrogen bonds, and ionic bonds.
Compare them in terms of the mechanisms by which they form and
their relative bond strengths.
5.
Explain how hydrogen bonds between adjacent water molecules
govern many of the properties of water.
6.
Explain how water ionizes and contrast acids and bases
7.
Convert the hydrogen ion concentration of a solution to a pH value.
Describe how buffers help minimize changes in pH.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings