Transcript Chapter 2 Chemistry

CPI
Chapter 2
Chemistry
Topics:
Composition of Matter
Energy
Solutions
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Matter
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Has mass, occupies space
Mass – amount of matter in an object
Weight – the measure of the pull of gravity on
the mass of an object
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Mass & weight can be used synonymously on
Earth, but they are not the same thing
Element – simplest form of matter that cannot
be broken down by ordinary chemical means
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Matter, cont.
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Atom – simplest unit of an element retaining
all the properties of that element
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Composed of 3 subatomic particles:
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Proton, neutron, electron
Protons + neutrons in small, dense center (nucleus)
Electrons are moving near speed of light orbiting
nucleus; 3 x 108 m/s; electrons have more E as they
move away from nucleus
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Atoms
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Particle
Proton
Neutron
Electron
Location
Nucleus
Nucleus
Orbit
Charge
+
0
-
Mass (amu)
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1
1/1872
Atomic Number = # protons
Atomic Mass = # protons + # neutrons
Neutral atom: # protons = # electrons
Ion = charged atom caused by gain/loss of electrons
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Chemical Reactions
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Electrons – part of atom involved in chemical
rxns
Electrons found in energy levels in atom
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Level 1 – holds 2 electrons max
Level 2 – holds 8 electrons max
Level 3 – holds 8 electrons max
When outermost energy level is full, atom is
stable and unreactive
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Periodic Table
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Elements arranged on periodic table by increasing
atomic #
Metals on left, non-metals on right, transition metals
in middle, metalloids along “stair” line
Important info on table
Period # - how many energy levels in atom
Family # - how many valence electrons in atom (be
careful of transition & rare-earth elements)
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Practice
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Name 2 metalloids.
How many electrons in Ca?
Name any 3 elements with 4 valence electrons.
An atom has an atomic mass of 79.9 and an atomic
# of 35. How many electrons does it have, what is
its name?
Name 2 stable atoms & tell me why they are stable.
K has how many energy levels?
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Bonding
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Three types of chemical reactions are
possible
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Ionic bonding – transfer of electrons
Covalent bonding – sharing of electrons
Metallic bonding – bonding of metals
In biology, we are concerned with ionic &
covalent bonding
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Ionic Bonding
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Occurs when a metal and a non-metal bond
Metal donates electron(s); non-metal accepts electron(s)
Metals have few valence electrons that are loosely held; so
easily donated
Non-metals have many valence electrons tightly held; so
electronegativity of these atoms is strong and they accept
electrons
Ions formed (metal +, non-metal -)
Ionically bonded compounds when dissolved in water will
conduct electricity; ions dissociate forming electrolytes
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Covalent Bonds
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Occurs when non-metals bond
These atoms have high electronegativity and
so tend to strongly hold electrons; thus these
atoms tend to share rather than donate to
each other
Molecule formed; no overall charge on unit
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Energy
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Ability to do work, cause change
Types:
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Chemical – E in bonds
Thermal – Heat E
Electrical – E of charges
Mechanical – E of motion
Free Energy – E in a system available for
work; E available to fuel cell rxns
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States of Matter
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States: solid, liquid, gas
E increases from solid to gas
Solid: definite volume & shape
Liquid: definite volume & indef shape
Gas: indefinite volume & shape
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Phase Change Diagram
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Phase change for Water, H2O
G
EP 
Temp
C
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MP 
S
L
CP 
FP 
Energy, KCal/Mole 
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Chemical Reactions
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Chemical rxns are like math equations (Yippee!)
CO2 + H2O  H2CO3
 Reactants
 Products
 Double Arrow – indicates rxn
proceeds both ways (reversible)
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Not all rxns are reversible
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Chemical Reactions, cont
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Governed by Law of Conservation of Mass &
Energy
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Reactants = Products
Chemical symbols – refer to elements
Arrow () is the = sign
Subscripts – tell how many of each element;
H 2O
Coefficients – tell how many molecules;
3CO2
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Reactions in Cells
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Homeostasis must be maintained
But rxn must proceed and E is required to
begin rxn
E required is Activation Energy
A rxn having a net release of free energy is
exergonic (exothermic)
A rxn having a net aborption of free energy is
endergonic (endothermic)
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Activation Energy
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Graph shows the E needed to begin a rxn to form products
AE = Activation E
E
Req
Reactants
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AE
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Products
E
Rel
Reaction 
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Activation Energy
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Problem – biological system not compatible with
high energy required to begin and sustain a reaction
Solution – add a CATALYST
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A chemical that speeds up a rxn, is not used up in the rxn,
can be used repeatedly, works by lowering the activation
energy
Biological catalysts are ENZYMES
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Proteins that speed reactions by lowering AE, can be used
repeatedly
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Another Look at AE
E
Req
New Lower AE
Reactants

Reaction 
Products
E
Rel
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Redox Rxns
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Short-hand term for “oxidation & reduction”
reactions
Rxns where electrons are transferred
between atoms
Always occur together
Oxidation rxn – reactant loses e- taking a +
charge
Reduction rxn – reactant gains e- taking a charge
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Solutions
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Homogeneous mixture
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Solute – substance being dissolved
Solvent – substance doing dissolving
Often it is a solid in a liquid; any phase of matter may be
dissolved in any phase, examples?
Concentration – measure of how much solute
dissolved in a solvent
Ways to measure concentration
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% solution
Molarity
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Solutions
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Saturated solution – a solution in which as
much solute as possible is dissolved;
temperature dependent
Unsaturated solution – a solution having less
than the total possible amount of solute
dissolved
Aqueous solution – a solution in which water
is the solvent
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Water
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Universal solvent (dissolves a wide range of solutes)
Polar molecule
O
H H
+
Oxygen side slightly negative; hydrogen side is
slightly positive
H2O molecules will align to maximize +/- interactions
and minimize -/- & +/+ interactions
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pH
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H2O will spontaneously dissociate into H+
and OH- ions; ions associate back into water
molecules; equilibrium is reached; pH = 7
In solution, excess H+ ions makes it acidic
In solution, excess OH- ions makes it basic
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pH
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Acids – sour, corrosive
Bases – bitter, corrosive
Scale:
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0 to 14; 7 is neutral
Log scale
pH 7 = 7.0 x 10 -7 H+ in solution
1 unit of change = a 10x change in amount of ions in
solution
pH 4 acid has 10x more H+ in solution than pH 5
solution & 100x more H+ than a solution of pH 6
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Neutralization
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Add a base to an acid – they neutralize each
other
Rxn yields a salt and water
A buffer another term for a base and it
neutralizes acids
Very important to biological systems; need to
maintain proper pH of any particular system
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Lab Reading Quiz
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1. pH measures _______________.
2. Acids release ________ when in solution.
3. Bases release _________ when in solution.
4. A solution with a pH of 4 has ____ times as many
hydrogen ions in solution as pH 5.
5. Acids taste _________.
Bonus: Name 2 ways to test pH.
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pH Quiz Answers
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1. conc of H+/OH- in solution; how
acidic/basic a solution is
2. H+ ions
3. OH- ions
4. 10
5. tart
B. pH meter, litmus paper, pH paper, indicator
solutions
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