chapter 2 chemistry of life1.pdf
TRANSCRIPT
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Chapter 2
The Chemistry of Life/ water
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Section 1
The nature of matter
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Objectives
What three subatomic particles make up atoms?
How are all the isotopes of an element similar?
What are the two types of chemical bonds?
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The Big Idea Life Depends on chemistry Chemical reactions keep you
alive
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Atom Basic unit of matter
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Democrites
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Subatomic particles Protons - Neutrons - Electrons -
Positively charged (+)Not charged (neutral)Negatively charged (-)
Bind together to form the nucleus
Electrons Protons
Neutrons
Nucleus
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Element A pure substance that consists
of just one type of atom
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6CCarbon12.011
Atomic number
An elements atomic number = number of protons
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Isotope Atoms of the same element
that differ in the number of neutrons they contain
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Nonradioactive carbon-12 Nonradioactive carbon-13 Radioactive carbon-14
6 electrons6 protons6 neutrons
6 electrons6 protons8 neutrons
6 electrons6 protons7 neutrons
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6CCarbon12.011 Mass number
The Sum of protons and neutrons in the nucleus of an atom is its mass number
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The weighted average of the masses of an elements isotope is called its atomic mass
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Radioactive isotopes Can be dangerous Can be used
practically forRadioactive datingTreat cancerKill bacteria
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Compounds A substance formed by the
chemical combination of two or more elements in definite proportions
Ex) H2O, NaCl
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Table Salt
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Covalent Bond and Ionic Bond Ionic bond: electron transfer Covalent bond: electron sharing
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Ionic Bonds Formed when one or more
electrons are transferred from one atom to another
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Sodium Chloride: ionic bond formation
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Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+) Chloride ion (Cl-)
Transferof electron
Protons +11Electrons -11Charge 0
Protons +17Electrons -17Charge 0
Protons +11Electrons -10Charge +1
Protons +17Electrons -18Charge -1
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If an atom loses an electron it becomes positive
If an atom gains an electron it becomes negative
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Ions Positively and negatively
charged atoms Positively charged ion is called
anode Negatively charged ion is
called cathode
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Molecule The structure that results when
atoms are joined together by a covalent bond
Smallest unit of most compounds
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Van der Waals Forces A slight attraction that
develops between the oppositely charged regions of nearby molecules due to unequal sharing of electrons
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The Van der Waals forces
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Homework
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1. Describe the structure of an atom.Atoms are made up of protons and
neutrons in a nucleus. Electrons are
in constant motion in the space
around the nucleus.
2. Why do all isotopes of an element have the same chemical propertiesThey have the same number of
electrons
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3. What is a covalent bond? A bond formed when electrons are shared between atoms
4. What is a compound? How are they related to moleculesA compound is a substance formed
by the chemical combination of two or
more elements in definite proportions.
A molecule is the smallest unit of
most compounds
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5. How do Van der Waals forces hold molecules together?When the sharing of electrons
are unequal, a molecule has
regions that are charged. An
attraction can occur between
oppositely charged regions of
nearby molecules
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6. How are ionic bonds and Van der Waals forces similar? How are they different?In both cases, particles are
held together by attractions
between opposite charges.
The difference is that ionic
charges are stronger
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Section 2:
Chemistry of water
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Objectives Why are water molecules polar? What are acidic solutions? What
are basic solutions? Correlation between water & life
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The Big Idea
Much of our planet is covered in water
Water is necessary for life to exist If life exists on other planets,
there most likely is water present Water has many properties that
make life possible
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Polarity(-)
(+)
The oxygen atom has a stronger attraction for electrons
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Hydrogen Bonds Because of waters partial charges,
they can attract each other and create hydrogen bonds
Not as strong as covalent or ionic bonds
Waters ability to create multiple hydrogen bonds gives it many special properties
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Cohesion Attraction between molecules of
the same substance
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Adhesion Attraction between molecules of
different substances.
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Correlation between water & life
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Mixture Material composed of two or more
elements or compounds that are physically mixed but not chemically combined
Ex.) salt & pepper, earths atmosphere
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Solutions Mixture of two or more
substances in which the molecules are evenly distributed
Ex.) salt water Settles out over time
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Solutions
Cl-
Water
Cl-
Na+
Water
Na+
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Solute Substance that is dissolved Ex.) salt
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Solvent The substance that does the
dissolving Ex.) Water
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Suspensions Mixture of water and non-
dissolved materials Ex.) sugar solution, blood Separate into pieces so small,
they never settle out
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The pH scale Indicated the concentration of
hydrogen ions in a solution
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Neutral
Acid
Base
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Acids Any compound that forms H+
(hydrogen) ions in solution
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Base A compound that produces OH-
(hydroxide) ions in solution
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Buffers Weak acids or bases that can
react with strong acids or bases to prevent sharp, sudden pH changes
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Homework
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1. Use the structure of a water molecule to explain why its polarOxygen atom has greater
attraction for electrons, therefore
the oxygen atom is negative and
the hydrogen end is positive
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2. Compare acidic and basic solutions in terms of their H+ ion and OH- ion concentrationsAcid have more H
+
ions than OH
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ions, and bases have more OH
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ions than H
+
ions
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3. What is the difference between a solution and a suspension?In a solution, all components are
evenly distributed. In a
suspension, un-dissolved
particles are suspended
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4. What does pH measure?The concentration of H
+
ions in a
solution
5. The strong acid hydrogen floride (HF) can be dissolved in pure water. Will the pH of the solution be greater or less than 7? less than 7
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The Big Idea Living things are made up of
chemical compounds Everything that happens to an
organism is based on chemical reactions
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Chemical Reactions A process that changes or
transforms one set of chemicals into another
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Reactants Elements or compounds that
enter into a reaction
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Products Elements or compounds
produced by a chemical reaction
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Example Reaction: Getting rid of carbon dioxide
In the blood
In the lungs
CO2 + H20 H2CO3 (carbonic acid)
H2CO3 CO2 + H2OReleased as you breathe
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Energy in reactions Energy-Absorbing Reaction Energy-Releasing Reaction
Products
Products
Activation energy
Activation energy
Reactants
Reactants
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Activation Energy The energy that is needed to get
a reaction started
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Enzymes Some chemical reactions are too
slow or have activation energies that are too high to make them practical for living tissue
These chemical reactions are made possible by catalysts
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Catalyst Substance that speeds up the
rate of chemical reactions Work by lowering a reactions
activation energy
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Enzyme Biological catalysts Speed up reactions in cells Very specific Named for the reaction is catylzes Enzyme names always end in -
ase
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Reaction pathwaywithout enzyme Activation energy
without enzyme
Activationenergywith enzyme
Reaction pathwaywith enzyme
Reactants
Products
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Substrates The reactants of enzyme
catalyzed reactions The active site of the enzyme and
the substrate have complementary shapes
Fit like a lock and key
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Enzyme Action
Enzyme substrate complex
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Glucose
Substrates
ATP
Substratesbind toenzyme
Substratesare convertedinto products
Enzyme-substratecomplex
Enzyme(hexokinase)ADP
Products
Glucose-6-phosphate
Productsare released
Active site
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Regulation of Enzyme Activity
Enzymes are affected by any variable that affects chemical reactions
1. pH2. Temperature3. Concentration
of enzyme
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Homework
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1. What happens to chemical bonds during chemical reactionsBonds are broken in reactants and
new bonds are formed in products
2. Describe the role of energy in chemical reactionssome chemical reactions release
energy, and other chemical
reactions absorb energy. Energy
changes determine how easily a
chemical reaction will occur
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3. What are enzymes, and how are they important to living things?Enzymes are biological catylasts.
Cells use enzymes to speed up
virtually every important chemical
reaction that takes place in cells
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4. Describe how enzymes work, including the role of the enzyme substrate complexSubstrates, the reactants of an
enzyme-catylzed reaction, attach
to the enzyme at an active site
and form an enzyme substrate
complex. Once the complex is
formed, the enzyme helps convert
substrate into product
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5. A change in pH can change the protein. How might a change in pH affect the function of an enzyme such as hexokinase (hint: think about the analogy of the lock and key)A change in pH could change the
shape of hexokinase. This change
would diminish the ability of glucose
and ATP to bind to the active site of
the enzyme.