CHEMISTRY
Composition of Matter

Matter - Everything in
universe is composed of
matter
 Matter is anything that
occupies space or has
mass
 Mass – quantity of
matter an object has
 Weight – pull of
gravity on an object
Elements

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Pure substances that cannot be broken
down chemically into simpler kinds of
matter
More than 100 elements (92 naturally
occurring)

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90% of the mass of an
organism is composed of 4
elements (oxygen, carbon,
hydrogen and nitrogen)
Each element unique
chemical symbol
 Consists of 1-2 letters
 First letter is always
capitalized
Atoms
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The simplest particle of
an element that retains
all the properties of that
element
Properties of atoms
determine the structure
and properties of the
matter they compose
Our understanding of the
structure of atoms based
on scientific models, not
observation
The Nucleus

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Central core
Consists of positive
charged protons
and neutral
neutrons
Positively charged
Contains most of
the mass of the
atom
The Protons

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All atoms of a given element have the
same number of protons
Number of protons called the atomic
number
Number of protons balanced by an equal
number of negatively charged electrons
The Neutrons

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The number varies slightly among atoms
of the same element
Different number of neutrons produces
isotopes of the same element
Atomic Mass

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Protons & neutrons are found in the
nucleus of an atom
Protons and neutrons each have a
mass of 1 amu (atomic mass unit)
The atomic mass of an atom is found
by adding the number of protons &
neutrons in an atom
The Electrons

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Negatively charged high energy particles
with little or no mass
Travel at very high speeds at various
distances (energy levels) from the
nucleus
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Electrons in the same energy level
are approximately the same distance
from the nucleus
Outer energy levels have more
energy than inner levels
Each level holds only a certain
number of electrons
Energy Levels

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Atoms have 7 energy levels
The levels are K (closest to the
nucleus), L, M, N, O, P, Q
(furthest from the nucleus)
The K level can only hold 2
electrons
Levels L – Q can hold 8 electrons
(octet rule)
Periodic Table

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Elements are arranged by their
atomic number on the Periodic Table
The horizontal rows are called
Periods & tell the number of
energy levels
Vertical groups are called Families &
tell the outermost number of
electrons
Compounds

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Most
elements do
not exist by
themselves
Readily
combine with
other
elements in
a
predictable
fashion

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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

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Molecules are the
simplest part of
a substance that
retains all of the
properties of the
substance and
exists in a free
state
Some molecules
are large and
complex
Chemical Formulas

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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 physical
and chemical
properties of
a compound
differ from
the physical
and chemical
properties of
the individual
elements that
compose it

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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 filled
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Most atoms are not stable
in their natural state
Tend to react (combine)
with other atoms in order
to become more stable
(undergo chemical
reactions)
In chemical reactions
bonds are broken; atoms
rearranged and new
chemical bonds are
formed that store energy
Covalent Bonds

Formed when two atoms share one or
more pairs of electrons
Ionic Bonds

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Some atoms become stable by losing or
gaining electrons
Atoms that lose electrons are called
positive ions

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Atoms that gain electrons are called
negative ions
Because positive and negative electrical
charges attract each other ionic bonds
form
Energy and Matter

Energy
 The ability to do work or cause
change
 Occurs in various forms
 Can be converted to another form
 Forms important to biological
systems are chemical, thermal,
electrical and mechanical energy
 Free energy is the energy in a
system that is available for work
States of Matter

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Atoms are in constant motion
The rate at which atoms or molecules in
a substance move determines its state

Solid
 Molecules
tightly linked together in
a definite shape
 Vibrate in place
 Fixed volume and shape

Liquids
 Molecules
not as tightly linked
as a solid
 Maintain fixed volume
 Able to flow and conform to
shape of container
Gas
Molecules have little
or no attraction to each
other
 Fill the volume of the
occupied container
 Move most rapidly
 To cause a substance to
change state, thermal energy
(heat) must be added to or
removed from a substance

Energy and Chemical Reactions

Living things
undergo
thousands of
chemical
reactions as part
of the life
process

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Many are very complex
involving multistep
sequences called
biochemical pathways
Chemical equations
represent chemical
reactions
Reactants are shown on the
left side of the equation
Products are shown on the
right side
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The number of
each kind of atom
must be the same
on either side of
the arrow
(equation must be
balanced)
Bonds may be
broken or made
forming new
compounds
Energy Transfer

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Much of the energy
organisms need is
provided by sugar (food)
Undergoes a series of
chemical reactions in
which energy is released
(cell respiration)
The net release of free
energy is called an
exergonic (exothermic)
reaction

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Reactions that involve
a net absorption of
free energy are called
endergonic
(endothermic)
reactions
Photosynthesis is an
example
Most reactions in living
organisms are
endergonic; therefore
living organisms
require a constant
source of energy

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Most chemical reactions require energy
to begin
The amount of energy needed to start
the reaction is called activation energy

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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

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Enzymes work on
substances called
substrates
Substrates must fit
into a place on an
enzyme called the
active site
Enzymes are reusable!
Reduction-Oxidation Reactions

Many of the chemical reactions that
help transfer energy in living organisms
involve the transfer of electrons
(reduction-oxidation = redox reactions)

Oxidation reaction – reactant loses
electron(s) becoming more positive

Reduction reaction – reactant gains
electron(s) becoming more negative
Solutions
Solutions

A solution is a
mixture in
which 2 or
more
substances are
uniformly
distributed in
another
substance

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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
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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)
 H2O  H+ (hydrogen
ion) + OH- (hydroxide
ion)

H+ + H2O  H3O
(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
 HCl  H+ + Cl-
Bases

Number of hydroxide ions in solution is
greater than the number of hydronium
ions
 NaOH  Na+ + OH-
pH Scale


logarithmic
scale for
comparing the
relative
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

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the lower the pH the stronger the acid
the higher the pH the stronger the base
pH 7.0 is neutral
Buffers

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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