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Composition of Matter
Matter - Everything in
universe is composed of
 Matter is anything that
occupies space or has
 Mass – quantity of
matter an object has
 Weight – pull of
gravity on an object
Pure substances that cannot be broken
down chemically into simpler kinds of
More than 100 elements (92 naturally
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
The smallest particle of
an element that retains
all the properties of that
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
The Nucleus
2 main regions: Central
core & electron shell
Consists of positive
charged protons and
neutral neutrons
Nucleus is positively
Contains most of the
mass of the atom
The Protons
All atoms of a given element have the
same number of protons
Number of protons called/determines
the atomic number
Number of protons balanced by an equal
number of negatively charged electrons
The Neutrons
The number varies slightly among atoms
of the same element
Different number of neutrons produces
isotopes of the same element
Atomic Mass
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
Negatively charged high energy particles
with little or no mass
Travel at very high speeds at various
distances (energy levels) from the
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
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
Levels L – Q can hold 8 electrons
(octet rule)
Periodic Table
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
elements do
not exist by
combine with
elements in
A compound is a pure
substance made up of
atoms of two or more
 The proportion of
atoms are always
Chemical formula shows
the kind and proportion
of atoms of each
element that occurs in a
particular compound
Molecules are the
simplest part of
a substance that
retains all of the
properties of the
substance and
exists in a free
Some molecules
are large and
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 physical
and chemical
properties of
a compound
are different
from the
physical and
properties of
the individual
elements that
compose it.
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 &
won’t react with other
Most atoms are not stable
in their natural state
Tend to react (combine)
with other atoms in order
to become more stable
(undergo chemical
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
Some atoms become stable by losing or
gaining electrons. These atoms are
called Ions.
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
States of Matter
Atoms are in constant motion
The rate at which atoms or molecules in
a substance move determines its state.
 Molecules
tightly linked together in
a definite shape
 Vibrate in place
 Fixed volume and shape
 Molecules
not as tightly linked
as a solid
 Maintain fixed volume
 Able to flow and conform to
shape of container
Molecules have little
or no attraction to each
 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
A solution is a
mixture in
which 2 or
substances are
distributed in
Solute is the
dissolved in the
 Particles may
be ions, atoms,
or molecules
Solvent is the
substance in which
the solute is
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 as
solvent) 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
Acids and Bases
One of the most important aspects of a
living system is the degree of acidity or
Number of hydrogen ions in solutions is
greater than the number of hydroxide
 HCl  H+ + Cl-
Number of hydroxide ions in solution is
greater than the number of hydronium
 NaOH  Na+ + OH-
pH Scale
scale for
comparing the
of hydrogen
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
Control of pH is very
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
Complex buffering
systems maintain
the pH values of
your body’s many
fluids at normal and
safe levels