Ch.2 Chemistry of Life
Nature of Matter
Atoms are made up of three
subatomic particles
1. Protons – Positive charge
2. Neutrons – Neutral charge
3. Electrons – Negative charge
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Protons and Neutrons are found in
the center of the atom called the
Nucleus.
Electrons are in constant motion in
the space surrounding the nucleus.
Atoms have an equal number of
protons and electrons so all atoms
have no net charge (neutral charge)
Elements
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A chemical element is a pure
substance that consists entirely
of one type of atom.
There are more than 100
known elements, however only
about 2 dozen are commonly
found in organisms.
Elements are represented by a
one or two letter symbol Ex.
Carbon=C, Sodium=Na
Atomic number the number
of protons in the element
Atomic mass the number of
protons plus neutrons rounded
to whole number
Isotopes
Atoms of the element that differ
in the number of neutrons they
contain are called isotopes.
 All the isotopes of an element have
the same number of electrons so
they have the same chemical
properties.
 Some isotopes are radioactive
meaning that their nuclei are
unstable and break down at a
constant rate over time.
 Radioactive isotopes have a
number of important scientific uses
Ex: determine the age of rocks and
fossils, treat cancer, kill bacteria,
and can be used as tracers to
follow movements of substances
within organisms.
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Chemical Compounds
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1.
2.
A chemical compound is a
substance formed by the chemical
combination of two or more
elements in definite proportions.
Chemical formula is a shorthand
way of writing the chemical
composition of compounds. Ex:
H2O
The physical and chemical
properties of a compound are
usually very different from those of
the elements from which it is
formed.
The atoms in compounds are held
together by chemical bonds -2
main types
Ionic bonds
Covalent bonds
Ionic bond
Covalent bond
Chemical Bonding
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The interactions of atoms from individual elements
form chemical compounds is called chemical bonding.
Chemical bonding occurs when atoms share, gain or
lose electrons.
An atom will bond with another atom if the bonding
gives both atoms complete outermost energy level.
The maximum number of electrons on the outermost
energy level is shown as : 1st level= 2; 2nd level= 8;
3rd level= 8 ; etc.
Ionic Bonding
Ionic bonding occurs when
electrons are transfer
(gained or lost) between
two atoms.
 Ionic bonding generally
occur between metals and
nonmetals.
 Elements that lose or gain
an electron become Ions
which now have an electrical
charges.
Na+ Cl
Covalent Bonding
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Covalent bonding occurs
when atoms shared
electrons.
Covalent bond generally
occur between nonmetals,
except when hydrogen
bonds with another
nonmetal in column #17
then it is an ionic bond.
Example: HCl
Van der Waals Forces
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Some atoms have a stronger attraction
for electrons than do other atoms.
Even when atoms in a covalent bond
share electrons the share is not always
equal.
The rapid movement of electrons can
create regions on a molecule that have a
tiny positive or negative charge.
When molecules are close together, a
slight attraction can develop between the
oppositely charged regions of nearby
molecules and these are called van der
Waals forces.
Although these forces are not as strong
as ionic bods or covalent bonds, they can
hold molecules together, especially when
the molecules are large
Water
Water is the single most abundant
compound in most living things.
 A water molecule is polar
because there is an uneven
distribution of electrons between
the oxygen and hydrogen atoms
 Water therefore has some very
unique properties:
1. Cohesion – attraction between
molecules of the same substance
Ex: water to water
2. Adhesion – attraction between
molecules of different
substances Ex: water to glass
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Solutions and Suspensions
Mixture – a material composed of
two or more elements or
compounds that are physically
mixed together but not chemically
combined. There are two types of
mixtures:
1. Solutions – when the
components are evenly
distributed throughout the
solution.
a. solute – the substance that
is dissolved
b. solvent – the substance in
which the solute dissolves
2. Suspensions – a mixture of
water and nondissolved material
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Acids, Bases, and pH
Acids – are any compounds
that forms H+ ions in
solution (pH less than 7)
 Bases – are any compounds
that produce hydroxide ions
OH- in solution (pH above
7)
 Buffers are weak acids or
bases that can react with
strong acids or bases to
prevent sharp, sudden
changes in pH
 pH scale – a system used to
indicate the concentration
of H+ ions in a solution
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Carbon Compounds (Organic Chemistry)
There are four groups of organic
compounds found in living things
1. Carbohydrates – used as main source
of energy in organisms, and some use
them for structural purposes
2. Lipids – (fats) used to store energy,
make up membranes and waterproof
coverings
3. Nucleic Acids – (DNA, RNA) store
and transmit heredity, or genetic,
information
4. Proteins – form bones and muscles,
cellular transport, help fight disease,
and some control the rate of
reactions and regulate cell processes.
Chemical Equations
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A
Chemical
equation is
a
shorthand
method of
showing a
chemical
reaction
Symbols and formulas are used to
represent reactants and products.
Reactants are chemicals that enter
into a reaction.
Products are the substance that is
produce from a reaction.
An Arrow, which is read “yields”
shows the direction of the reaction.
Chemical reactions are reversible.
Endothermic & Exothermic
Reactions
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Exothermic reaction
C6H12O6 + 602 
(reactants)
(yield)
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6CO2 + 6H2O + Energy
(product)
Endothermic reaction
Light Energy + 6CO2 + 6H2O 
(reactants)
(yield)
C6H12O6 + 6O2
(product)
Balancing Chemical Equations
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Atoms can be neither created nor destroyed by
ordinary chemical reactions.
Atoms will only change positions or form other
compounds during a chemical reaction.
If you start a reaction with a certain number of atoms in
the reactants you will end with the same amount of
atoms in the products of a chemical reaction. This is
called balancing chemical equations
H2 + O 
2 Hydrogen
1 Oxygen
H2 O
2 Hydrogen
1 Oxygen
Balancing Equations (con’t)
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Fe2O3 + 3C  3CO + 2Fe
The large numbers in front of chemical formulas in
equations are called coefficients. Coefficients represent the
number of molecules.
The small numbers to the lower
right of chemical symbols are called subscripts. Subscripts
represent the number of atoms.
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Equations are balanced by changing coefficients never by
changing subscripts.
An equation is not properly balanced if the coefficients are
not written in lowest whole number ratio.
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Diatomic Molecules
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Hydrogen H2
Nitrogen
N2
Oxygen
O2
Fluorine
F2
Chlorine Cl2
Iodine
I2
Bromine
Br2
When these elements are
found by themselves in a
chemical equation, they
must have subscript of 2.
Balance these equations
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1. ___ Na + ___ Cl2  ___ NaCl
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2. ___S8 + ___ O2  ___SO3
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3. ___HgO  ___Hg + O2
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4. ___Al + ___FeO  ___Fe +
___Al2O3
Key to Equations
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1. 2Na + Cl2  2 NaCl
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2. S8 + 12O2  8SO3
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3. 2HgO  2Hg + O2
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4. 2Al + 3FeO  3Fe + Al2O3
Enzymes
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Enzymes speed up chemical
reactions that take place in cells,
also called catalysts
Enzymes provide a site where
reactants can be brought together
to react
Such a site reduces the energy
needed for the reaction
The reactants of enzyme-catalyzed
reaction are known as substrates
Enzymes are very important, they
play essential roles in regulation
chemical pathways, making
materials that cells need, releasing
energy, and transferring information