CHEMISTRY
Elements
• Pure substances that cannot be broken
down chemically into simpler kinds of
matter
• More than 100 elements (92 naturally
occurring)
• 90% of the mass of an
organism is composed
of 4 elements (oxygen,
carbon, hydrogen and
nitrogen)
• A compound is a pure substance made up of
atoms of two or more elements
– The proportion of atoms are always fixed
• Chemical formula shows the kind and
proportion of atoms of each element that
occurs in a particular compound
C6H12O6
+
6O2

6H2O +6CO2 + 36ATP
subscripts
Coefficient
• Molecules are the
simplest part of a
compound that
retains all of the
properties of the
substance and
exists in a free
state
• Some molecules
are large and
complex
Chemical Formulas
• Subscript after a symbol tell the
number of atoms of each element
• H20 has 2 atoms of hydrogen & 1
atom of oxygen
• Coefficients before a formula tell the
number of molecules
• 3O2 represents 3 molecules of oxygen
or (3x2) or 6 atoms of oxygen
• The tendency of
elements to combine and
form compounds depends
on the number and
arrangement of
electrons in their
outermost energy level
• Atoms are most stable
when their outer most
energy level is full
• Most atoms are not
stable in their natural
state (If they’re full,
they won’t react)
• Tend to react
(combine) with other
atoms in order to
become more stable
(undergo chemical
reactions)
1. What are the 4 most common
elements found in living things?
a.
b.
c.
d.
Hydrogen, sulfur, phosporous, calcium
Nitrogen, hydorgen, carbon, oxygen
Oxygen, sulfur, hydrogen, calcium
Carbon, hydrogen, phosphorous,
nitrogen
Bonding with the four main
Elements
•
•
•
•
H-needs 1 electron
O-needs 2 electrons
N- needs 3 electrons
C- needs 4 electron
C6H12O6 + 6O2
Reactants

6H2O +6CO2 + 36ATP
Products
Chemical equations represent chemical
reactions.
Covalent Bonds
• Formed when two atoms share one or
more pairs of electrons
Ionic Bonds
• Some atoms become stable by losing or
gaining electrons
• Atoms that lose electrons are called
positive ions
• Atoms that gain electrons are called
negative ions
• Because positive and negative electrical
charges attract each other ionic bonds
form
2. Why do atoms form bonds?
a. To change from a gaseous state
b. To become more stable
c. To build larger molecules
d. To gather more electrons
Energy and Matter
• Energy
– The ability to do work or cause
change
– Can be converted to another
form
Energy and Chemical Reactions
• Living things
undergo thousands
of chemical
reactions as part
of the life process
(Metabolism)
Energy Transfer
• Much of the energy
organisms need is
provided by sugar
(glucose)
• Undergoes a series of
chemical reactions in
which energy is
released (cell
respiration)
3. How many bonds can carbon
atoms form?
A.
B.
C.
D.
1
2
3
4
4. Where are reactants found in a
chemical equation?
a.
b.
c.
d.
On the left side
On the right side
Beneath the arrow
Above the arrow
• Most chemical reactions require energy
to begin
• The amount of energy needed to start
the reaction is called activation energy
• Certain chemical
substances (catalysts)
reduce the amount of
activation energy
required
• Biological catalysts are
called enzymes
• Enzymes are an important class of
catalysts in living organisms
– Mostly protein
– Thousands of different kinds
– Each specific for a different
chemical reaction
Enzyme Structure
• Enzymes work on
substances called
substrates
• Substrates must fit into
a place on an enzyme
called the active site
• Enzymes are reusable!
5. The place on the enzyme into which the
substrate fits is the __________ site.
a.
b.
c.
d.
Reaction
Metabolizing
Catalyzing
Active
Solutions
Solutions
• A solution is a
mixture in which
2 or more
substances are
uniformly
distributed in
another
substance
6. An enzyme is a(n)
a. Protein
b. Element
c. Substrate
d. atom
• Solute is the
substance dissolved
in the solution
– Particles may be
ions, atoms, or
molecules
• Solvent is the
substance in which
the solute is
dissolved
• Water is the
universal solvent
• Solutions can be composed
of varying proportions of a
given solute in a given
solvent --- vary in
concentration (measurement
of the amount of solute)
• A saturated solution is one
in which no more solute can
be dissolved
• Aqueous solution (water) are
universally important to
living things
• Dissociation of water
– Breaking apart of the
water molecule into two
ions of opposite charge
(due to strong attraction
of oxygen atom of one
molecule for H atom of
another water molecule)
– OH- (hydroxide ion)
– H+ (hydronium ion)
Acids and Bases
• One of the most important aspects of a
living system is the degree of acidity or
alkalinity
Acids
• Number of hydronium ions in solutions is
greater than the number of hydroxide ions
Bases
• Number of hydroxide ions in solution is
greater than the number of hydronium ions
pH Scale
• concentrations of
hydronium ions
and hydroxide
ions in a solution
• ranges from 0 to
14
 Each pH is 10X
stronger than next
 e.g. ph 1 is 10 times
stronger than ph 2
• the lower the pH the stronger the acid
• the higher the pH the stronger the base
• pH 7.0 is neutral
Buffers
• Control of pH is very
important
• Most enzymes function
only within a very narrow
pH
• Control is accomplished
with buffers made by the
body
• Buffers keep a neutral pH
(pH 7)
• Buffers neutralize
small amounts of
either an acid or
base added to a
solution
• Complex buffering
systems maintain the
pH values of your
body’s many fluids
at normal and safe
levels
7. A liquid that has a pH of 3 is a(n)
a. Acid
b. Base
c. Neutral
d. Ion