Chapter 3
“Chemistry of Life”
Atom
• The smallest particle of an element
Elements
• Pure substances that cannot be broken
down into simpler substances
• Fewer than 30 elements are important to
living things
• 90% of the mass of living things is made
up of only 4 elements
– Look on your periodic table and fill in these 4
elements
•
•
•
•
O_____________
C_____________
H_____________
N_____________
Chemical Symbols
• Combinations of
one or two
letters, derived
from Latin words
to represent
chemical
elements
Chemical Bonding
• Chemical reactions
occur between two or
more elements in ways
that tend to cause their
atoms to become stable
List the two types of bonds that can occur in
compounds (based upon whether the electrons are
transferred or shared) in the blanks for 1 & 2.
II. How are chemical reactions represented?
…by chemical Equations
Look on page 65 to fill in the substance that is changed in a
reaction and the new substance that is formed.
CO2 + H20  H2CO3
Reactants
_____________________
Yield Products
___________ _________________
Activation Energy: (text pg. 65)
• Question: What happens to the amount of
activation energy needed in a reaction when a
catalyst (also known as an enzyme) is used?
Look at the line graph.
Does the amount of
activation energy:
A. Increase (or)
B. Decrease (or)
C.Remain the same
…when an enzyme is
present?
III. Counting Atoms
• The number of atoms is indicated by
subscripts
O
H2O
=
H
Fill in the correct numbers of atoms for the
examples in the table on your note sheet after
looking at the example on the next slide:
H
When counting atoms be careful to correctly
use the subscripts as in this example:
• Al2 (SO3)3
•
•
•
•
•
•
How many Aluminum?
2
How many Sulfur?
3
How many Oxygen?
9
IV. Balancing Equations:
• An equation is NOT balanced until you have the same number
of atoms of each element on both sides of the yield sign.
• To balance an equation, Coefficients are used (whole numbers
placed in front of a reactant or product) are used. Do NOT change
the subscripts.
• What coefficients would you add to balance the equation below?
(write it out in the margin of your worksheet, and then check your answer)
CH4 + O2  CO2 + H2O
Where would you place the coefficients
to balance this equation?
(fill in your answer on the worksheet now)
2 2O
2 H2 + ___O2  ___H
___
V. Balance the 3 chemical equations on the next
page of the worksheet (A, B, & C) by adding
coefficients as in the example below:
VI. Acids & Bases
Solutions consist of:
Solute
_____________
= the substance that is dissolved
Solvent = the substance that does the dissolving
_____________
Water
________________ = the greatest solvent in the world
When ionically bonded compounds dissolve
in Water, they break apart into ions
Example: NaCl  Na+ + Cl-
Acids
• Compounds that
release hydrogen
ions into solution,
which react with
water to form
Hydronium Ions
(H3O+)
Example: HCl  H+ + Cl-
Bases
• Compounds that release Hydroxide Ions
into solution (OH-)
Example: NaOH  Na+ + OH-
pH Scale:
• A measurement system that indicates the
relative concentrations of :
• Hydronium ions (H30+)
• Hydroxide ions (OH-)
(The next 3 slides show various indicators
but are not on your worksheet)
Litmus paper test:
• Red to Blue = Base
• Blue to Red = Acid
pH Paper Test:
• Or wide range
paper, allows you to
see color changes
between 0-14.
Liquid Indicator Solutions:
Liquids that change color when the pH changes
(like the cabbage water activity)
What is present in solutions of living
things to prevent pH changes? (pg. 57)
• Human blood has a pH
of 7.4. If it dropped to
7.0 or went up to 7.8 we
would die. The cells of
our bodies are constantly
going through changes;
therefore, the buffer in
our blood functions to
maintain homeostasis, or
prevent big changes in
the pH.
Many chemical reactions in living things would not
occur without the help of enzymes.
(Refer to page 66-67 to fill in the blanks regarding enzymes on the worksheet)
When you have finished your worksheet, show Mr.
Ryan and you may get your homework:
• For homework complete the “Acid / Base
Indicator” worksheet due on Friday.
• Don’t forget about the Study Island due
Friday!