Transcript Mader 11 ch 2 Basic Chemistry

Biology
Sylvia S. Mader
Michael Windelspecht
Chapter 2
Basic Chemistry
1
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Mader Chapter 2 ~ Basic Chemistry
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This chapter should be a review.
We will go over this material very
quickly.
Read second ½ of Ch 2 for
tomorrow.
You should also read appropriate
pages of CliffsAP
Take the Sample test on page 27,
grade it and turn in by Sept 2.
Topics
2.1 Chemical Elements
2.2 Compounds and Molecules
2.3 Chemistry of Water
2.4 Acids and Bases
Mills Biology 2001
2.1 Chemical Elements
• Matter is defined as anything that has mass
and occupies space.
• Matter exists in three states: solid, liquid, and
gas.
• All matter (both living and non-living) is
composed of elements.
3
Elements
• An element is a substance that cannot be broken down into
substances with different properties; composed of one type of
atom.
• Six elements make up 95% of the body weight of organisms:
(acronym CHNOPS)
 Carbon
 Hydrogen
 Nitrogen
 Oxygen
 Phosphorus
 Sulfur
4
Composition of Earth’s Crust and Its Organisms
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Percent by Weight
60
Earth’s crust
organisms
40
20
0
Fe Ca
K
S
P
Si Al Mg Na
Element
O
N
C
H
© Gunter Ziesler/Peter Arnold, Inc.
5
Atoms
• An atom is the smallest part of an element
that displays the property of the element.
• An element and its atom share the same name.
 Composed of subatomic particles: protons,
neutrons, electrons
 Central nucleus
• Protons- positively charged
• Neutrons- no charge
 Orbiting clouds around nucleus (electron shells)
• Electrons- negatively charged, very low massnegligible in calculations
6
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= proton
= neutron
= electron
a.
b.
Subatomic Particles
Atomic Mass Unit
(AMU)
Location
+1
1
Nucleus
Neutron
0
1
Nucleus
Electron
–1
0
Electron shell
Particle
Proton
Electric
Charge
7
c.
Atomic Number and Mass Number
• Each element is represented by one or two letters to give
it a unique atomic symbol.
 H = hydrogen, Na = sodium, C = carbon
• The atomic number is equal to the number of protons in
each atom of an element.
• The mass number of an atom is equal to the sum of the
number of protons and neutrons in atom’s nucleus.
 The atomic mass is approximately equal to the mass number.
8
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mass number
atomic number
atomic symbol
Atomic number?
Atomic mass?
9
Periodic Table
• Atoms of an element are arranged horizontally by
increasing atomic number in rows called periods.
• Atoms of an element arranged in vertical columns are
called groups.
 Atoms within the same group share the same binding
characteristics.
• Atoms shown in the periodic table are electrically neutral.
 Therefore, the atomic number tells you the number of electrons
as well as the number of protons.
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A Portion of the Periodic Table
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
I
1
Periods
2
3
4
1
H
VIII
atomic number
atomic mass
atomic symbol
2
He
1.008
II
III
IV
V
VI
VII
4.003
3
Li
4
Be
5
B
6
C
7
N
8
O
9
F
6.941
9.012
10.81
12.01
14.01
16.00
19.00
20.18
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
22.99
24.31
26.98
28.09
30.97
32.07
35.45
39.95
19
20
31
32
33
34
35
36
K
Ca
Ga
Ge
As
Se
Br
Kr
39.10
40.08
69.72
72.59
74.92
78.96
79.90
83.60
10
Ne
Groups
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2.1 Chemical Elements
Know highlighted elements
Mills Biology 2001
Isotopes
• Isotopes are atoms of the same element that
differ in the number of neutrons (and therefore
different atomic masses).
 Some isotopes spontaneously decay
• Radioactive isotopes give off energy in the form of rays and
subatomic particles
• Can be helpful or harmful
12
6
C
Carbon 12
13
6
C
Carbon 13
14
6
C
Carbon 14
13
Uses of Low
Levels of Radiation
Low levels of
radioactive
Iodine are used
to “see” the
thyroid gland.
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larynx
thyroid gland
trachea
a.
In a PET scan
an isotope of
glucose is used
to detect active
tissues.
b.
a: © Biomed Commun./Custom Medical Stock Photo; b (left) : Courtesy National Institutes of Health;
b: (right) © Mazzlota et al./Photo Researchers, Inc
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Uses of High Levels of Radiation
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a.
b.
a: (Peaches): © Tony Freeman/PhotoEdit; b: © Geoff Tompkinson/SPL/Photo Researchers, Inc.
15
Electrons and Energy
• Electrons are attracted to the positively charged nucleus, thus it
takes energy to hold electrons in place.
• It takes energy to push them away and keep them in their own shell.
 The more distant the shell, the more energy it takes to hold in place.
• Electrons have energy due to their relative position (potential
energy).
• Electrons determine chemical behavior of atoms.
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The Distribution of Electrons
• The Bohr model is a useful way to visualize electron
location.
 Electrons revolve around the nucleus in energy shells (energy
levels).
 For atoms with atomic numbers of 20 or less, the following rules
apply:
• the first energy shell can hold up to 2 electrons
• each additional shell can hold up to 8 electrons
• each lower shell is filled first before electrons are placed in
the next shell
 These rules cover most of the biologically significant
elements.
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Valence Electrons
• The outermost energy shell is called the valence shell.
• The valence shell is important because it determines many of an
atom’s chemical properties.
• The octet rule states that the outermost shell is most stable when it
has eight electrons.
•
 Exception: If an atom has only one shell, the outermost valence shell is
complete when it has two electrons.
The number of electrons in an atom’s valence shell determines whether the
atom gives up, accepts, or shares electrons to acquire eight electrons in the
outer shell.
– Atoms that have their valence shells filled with electrons tend to
be chemically stable.
– Atoms that do not have their valence shells filled with electrons
are chemically reactive.
18
Bohr Models of Atoms
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electron
electron shell
H
hydrogen
1H
1
valence shell
C
N
carbon
nitrogen
nucleus
12 C
6
14 N
7
P
S
O
oxygen
16
O
8
phosphorus
31
15 P
sulfur
32
16S
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2.2 Compounds and Molecules
• A molecule is two or more elements bonded together.
• A compound is a molecule containing at least two different elements
bonded together.
 CO2, H2O, C6H12O6, etc.
In Biology – usually used interchangeably (molecule and compound)
• A formula tells you the number of each kind of atom in a molecule.
one molecule
indicates 6 atoms
of carbon
indicates 12 atoms
of hydrogen
indicates 6 atoms
of oxygen
20
Chemical Bonding
• Bonds that exist between atoms in molecules contain
energy.
• Bonds between atoms are caused by the interactions
between electrons in outermost energy shells.
• The process of bond formation is called a chemical
reaction.
21
Types of Bonds
• Covalent bonds
• Ionic bonds
• Hydrogen bonds
• An ion is an atom that has lost or gained an electron.
• An ionic bond forms when electrons are transferred from one atom
to another atom and the oppositely charged ions are attracted to
one.
 Example: formation of sodium chloride
• Salts are solid substances that usually separate and exist as
individual ions in water.
22
Formation of Sodium Chloride
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Na
Cl
sodium atom (Na)
chlorine atom (Cl)
23
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Na
Cl
sodium atom (Na)
chlorine atom (Cl)
24
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Na
Cl
sodium atom (Na)
chlorine atom (Cl)
–
+
Na
Cl
sodium ion (Na+)
chloride ion (Cl–)
sodium chloride (NaCl)
25
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Na
Cl
sodium atom (Na)
chlorine atom (Cl)
–
+
Na
Cl
sodium ion (Na+)
chloride ion (Cl–)
Na+
Cl–
sodium chloride (NaCl)
a.
b.
b (middle): © Evelyn Jo Johnson; b (right): © Evelyn Jo Johnson
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Types of Bonds: Covalent Bonds
• Covalent bonds result when two atoms share electrons so each
atom has an octet of electrons in the outer shell.
 Note: In the case of hydrogen, the outer energy shell is complete
when it contains 2 electrons.
• In a nonpolar covalent bond electrons are shared equally
between atoms.
 Examples: hydrogen gas, oxygen gas, methane
27
Covalently
Bonded
Molecules
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Structural
Formula
Electron Model
H
H
H
Molecular
Formula
H2
H
a. Hydrogen gas
O
O
O
O2
O
b. Oxygen gas
H
H
H
C
H
H
C
H
CH4
H
H
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c. Methane
Types of Bonds: Covalent Bonds
• In a polar covalent bond electrons are shared unequally.
 Example: water
• Electronegativity is the ability of an atom to attract electrons
towards itself in a chemical bond.
 In water, the oxygen atom is more electronegative than the hydrogen
atoms and the bonds are polar.
Oxygen is partially negative
O
H
H
Hydrogens are partially positive
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30
2.3 Chemistry of Water
•
Water is a polar molecule.
 The shape of a water molecule and its polarity make hydrogen bonding possible.
•
A hydrogen bond is a weak attraction between a slightly positive hydrogen
atom and a slightly negative atom.
 Can occur between atoms of different molecules or within the same molecule
 A single hydrogen bond is easily broken while multiple hydrogen bonds are
collectively quite strong.
 Help to maintain the proper structure and function of complex molecules such as
proteins and DNA
31
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2.3 Chemistry of Water
Electron Model
Fig. 2.9
O
H
H
+
H
-
Ball-and-stick Model
O
H
+
hydrogen
bond
O
H
H
104.5˚
b. Hydrogen bonding between water molecules
Space-filling Model
Oxygen attracts the shared
electrons and is partially negative.
O
H
+
H
+
Hydrogens are partially positive.
a. Water (H2O)
32
2.3 Chemistry of Water
• Properties of water
 Makes up 60-80% of most living
cells
 Most abundant compound in living
tissue
 Makes up about 66% of weight of
an adult human
• About 75% of your brain is water!
• Why do we need it?
 Cohesion, adhesion, surface
tension, heat transfer, solvent,
transport, properties of freezing.
Mills Biology 2012
Properties of Water
• Water molecules cling together because of hydrogen bonding.
 This association gives water many of its unique chemical properties.
• Water has a high heat capacity.
 The presence of many hydrogen bonds allow water to absorb a large
amount of thermal heat without a great change in temperature.
 The temperature of water rises and falls slowly.
• Allows organisms to maintain internal temperatures
34
Temperature and Water
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800
Gas
Calories of Heat Energy / g
600
540
calories
400
200
Liquid
0
80
calories
Solid
freezing occurs
0
20
evaporation occurs
40
60
80
Temperature (°C)
100
120
a. Calories lost when 1 g of liquid water freezes and calories required when
1 g of liquid water evaporates.
b. Bodies of organisms cool when their heat is used to evaporate water.
b: © Grant Taylor/Stone/Getty Images
35
Properties of Water
• Water has a high heat of vaporization.
 Hydrogen bonds must be broken to evaporate water.
 Bodies of organisms cool when their heat is used to evaporate water.
• Water is a good solvent.
 Water is a good solvent because of its polarity.
 Polar substances dissolve readily in water.
 Hydrophilic molecules dissolve in water.
 Hydrophobic molecules do not dissolve in water.
36
Water as a Solvent
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H
O
H
H
O
Na+
H
O
H
An ionic salt
dissolves in water.
O
H
H
H
Cl–
H
O H
H
H
O
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Cohesion and Adhesion
• Cohesion
 Sticks to itself
 Polarity
• Caused by H bonds
• Without these bonds water would
boil at -80C (instead of +100) and
freeze at –100C (instead of 0C) this
would not be compatible with life
• Adhesion




Sticks to other substances
polarity
“add” hesion
Capillary action
High surface tension due to
hydrogen bonding of water.
Water as a Transport Medium
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Water evaporates,
pulling the water
column from the
roots to the leaves.
H2O
Water molecules
cling together and
adhere to sides of
vessels in stems.
Water enters a
plant at root cells.
H2O
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Properties of Water
• Ice is less dense than liquid water.
 At temperatures below 4°C, hydrogen bonds
between water molecules become more rigid
but also more open.
 Water expands as it reaches 0°C and freezes.
 Ice floats on liquid water.
• Acts as an insulator on top of a frozen body of
water
Ice floats, I’m glad!
40
Density of Water at Various Temperatures
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ice lattice
1.0
Density (g/cm3)
liquid water
0.9
0
4
Temperature (ºC)
100
41
A Pond in Winter
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ice layer
Protists provide
food for fish.
River otters visit
ice-covered ponds.
Aquatic insects survive
in air pockets.
Freshwater
fish take
oxygen
from water.
Common frogs and pond turtles hibernate.
42
2.4 Acids and Bases
•
pH is a measure of hydrogen ion concentration in a solution.
•
When water ionizes or dissociates, it releases an equal number of hydrogen
(H+) ions and hydroxide (OH-) ions.
Acids are substances that dissociate in water, releasing hydrogen ions.
Bases are substances that either take up hydrogen ions (H+) or release
hydroxide ions (OH−).
•
•
43
Soren Sorenson
1909 Beer Brewer
Developed pH scale
Mills Biology 2012
The pH Scale
• The pH scale is used to indicate the acidity or basicity (alkalinity) of
a solution.
 Values range from 0-14
• 0 to <7 = Acidic
• 7 = Neutral
• >7 to 14 = Basic (or alkaline)
• Actually a measure of H ion concentration (negative log of the H ion
concentration) (log is the power to which 10 must be raised to get a certain number)




measures grams of ion/liter of solution
pH is a shorthand measurement scale
wide range
10 fold change for each change in pH
pH of 1 = 10-1
pH of 6 = 10-6
• concentration of 0.1gm H ion/L = pH 1
 move decimal to left for each increase of 1 pH
45
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pure water, tears
3
H+
2
1
0 Acidic
NeutralpH
4
7 8
5 6
9
10
11
12
13
14
Basic
OH–
46
Buffers and pH
• A buffer is a chemical or a combination of chemicals that keeps pH
within normal limits.
• Health of organisms requires maintaining the pH of body fluids
within narrow limits.
 Human blood is normally pH 7.4 (slightly basic)
• If blood pH drops below 7.0, acidosis results
• If blood pH rises above 7.8, alkalosis results
• Both are life-threatening situations.
 Body has built-in mechanisms to prevent pH changes.
Read Connecting the Concepts with the Big Ideas pg 34
47
THE END
Mills Biology 2012