Unit
2
Matter,
Chemical Reactions,
and Solutions
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Chapter 6
MATTER, PROPERTIES,
AND PHASES
matter
MATTER and ATOMS
MATTER describes everything that we
can see, touch, smell, or feel. In other
words, mat ter is anything that has mass
and takes up space (including air and
almost everything else).
The smallest unit of matter is called
an ATOM. If you chop a piece of
metal into a bajillion pieces, the
smallest bit you are left with that
anything that
has mass and
takes up space
atom
the smallest
unit of matter
The word atom is
derived from a Greek
word that means
“cannot be divided.”
still has the properties of the metal
is called an atom.
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( And the Greeks
didn't even have a
particle accelerator!)
ATOMIC MODELS
Atoms are made of smaller particles:
Remember that a model is a
way to represent something
th at we can’t easily see.
PROTONS (positively charged particles)
NEUTRONS (electrically neutral particles,
which means they have no charge)
ELECTRONS (negatively charged particles with almost no mass)
nucleus
the center of an
atom, formed by
protons and neutrons
Protons and neutrons stick
together to form the center
of an atom, called the
NUCLEUS, which has a net
positive charge. Electrons
orbit, or circle around, the
nucleus, but too quickly to
pinpoint their exact locations.
The MODERN ATOMIC MODEL
shows an ELECTRON CLOUD rather
than individual electrons like
the model above. It demonstrates
where you’re most likely to find
an orbiting electron. Denser
areas of the cloud mean a higher
probability of electrons.
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Brief History of the Atomic Models
JOHN DALTON was the first scientist to propose that elements
are composed of indestructible atoms. He thought that there
were particles so small that we could not see them. He called
these particles atoms, and his theory on matter was known as
the ATOMIC THEORY OF MATTER.
SIR JOSEPH JOHN (J. J.) THOMSON discovered
the presence of negatively charged particles
(electrons) in atoms and pictured them
embedded with positively charged particles,
kind of like raisins in oatmeal-raisin cookies.
HELLO MY NAME
IS:
ERN EST
ERNEST RUTHERFORD worked out that each atom had a small
and heavy positively charged center, which he called a nucleus.
He figured out that electrons were orbiting the nucleus in
mostly empty space. He called the positive particles in the
nucleus protons. Rutherford’s student SIR JAMES CHADWICK
proposed the existence of uncharged particles in the nucleus,
which he called neutrons.
PHYSICAL and CHEMICAL
PROPERTIES and CHANGES
The way something looks, feels, smells, and tastes are all
PHYSICAL PROPERTIES. It's easy to classify matter by these
characteristics. Some common physical properties used to
differentiate matter are:
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HELLO MY
NAM E IS:
J. J.
COLOR
SIZE
DENSITY
MALLEABILITY (how easily something
can be flattened, shaped, or pressed)
MAGNETISM (whether or not something is magnetic)
BOILING POINT and MELTING POINT
(the temperature at which something boils or melts)
SOLUBILITY (how easily something dissolves
in another substance)
A PHYSICAL CHANGE is any change to the physical
properties of matter such as its size, shape, or state (solid,
liquid, or gas/vapor). The final product of any physical change
is still composed of the same matter. For example, you can
revert ice, snow, or vapor back to water by either heating or
cooling it. Ice, vapor, and water are all the same matter-just
in different states.
CHEMICAL PROPERTIES describe the ability of something
to undergo different chemical changes.
Some examples of chemical properties:
FLAMMABILITY (how easily
something lights on fire)
REACTIVITY (how reactive something
is to oxygen, water, light, etc.)
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When any of these chemical properties changes, the matter
has gone through a CHEMICAL CHANGE. Rust on an
iron gate or a log burning and
producing ashes are both examples
of chemical changes. Some signs of
chemical change
when matter changes into new
substances with new properties
chemical change may include:
CHANGE IN COLOR-This is like when you leave a sliced
apple out and it turns brown.
CHANGE IN ENERGY-The chemicals react, releasing
energy in the form of bright lights and heat.
Think of fireworks.
CHANGE IN ODOR
Think of food g oin g rotten.
FORMATION OF A GAS OR SOLID: When you add two
substances together, such as vinegar and baking soda, you
frequently see bubbles. Bubbles, or gas formation, are a sign
that the ingredients have undergone a chemical change.
Chemical changes are often much harder to reverse than physical
ones-just imagine trying to turn ashes back into a log of wood.
SYNTHETIC MATERIALS are materials that don’t occur in
nature, but are instead made from natural resources that undergo
a chemical change. For example, polyester is a synthetic fiber made
from air, water, coal, and petroleum. Acid and alcohol are used to
create a chemical reaction, which results in polyester fibers.
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Conservation of Mass
conservation
of mass
While things may change
appearance or composition during
physical and chemical changes,
one thing remains consistent:
The amount of mass at
the start of a reaction will
equal the amount of mass
after the reaction.
the amount of mat ter present.
This concept is called the CONSERVATION OF MASS. So
mass doesn’t just disappear-it still exists, but it may be in a
different form, like in the surrounding gases. The atoms have
just rearranged to form different substances.
The reactant is equal in
mass to the product.
reactant
substance that is changed in a
physical or chemical reaction
product
REACTANT
the resulting substance of a
physical or chemical reaction
PRODUCT
MASS
STATES of MATTER
Matter is usually found in three STATES (or PHASES): solid,
liquid, and vapor (or gas). The arrangement and behavior
of particles is what determines the state of matter. The
attraction between particles keeps particles close together,
and the energy of their movement allows particles to
overcome these attractive forces.
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A SOLID, like ice, wood, or metal, is
matter that has a defined shape and
volume. The particles in matter are
packed closely together, and they don’t move around freely,
which is why a solid has a defined shape and volume. Still,
particles in a solid vibrate back and forth, but not enough to
overcome the attractive force between particles.
LIQUIDS are free-flowing and assume the shape
of the container that holds them. Liquids, however,
do have a fixed volume. Particles in liquid move
around fast enough to overcome attractive forces. While the
liquid particles do move freely, they still stick together. The
speed at which a liquid flows depends on its VISCOSITY.
Viscosity is the resistance to flow.
VAPORS (or GASES) don’t have fixed
volume or shape. The shape and volume of
a gas depends on its container, and unlike
liquids, it will fill any container you place it
in. The molecules in gases spread really far
apart and move at high speeds. Gas molecules
move so quickly that they are able to overcome
at tractive forces between particles, which allows
the molecules to separate on their own. If you spilled the
gas from a balloon into the air, it would disperse evenly
into the air.
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state
featurES
MOVEMENT OF PARTICLES
SOLID
Fixed shape and volume
Vibrate, but have fixed positions
LIQUID
Shape can change, volume is
fixed. Can flow.
Free-moving—
no fixed positions.
GAS
Shape and volume not fixed and
depends on container. Can flow.
Particles move quickly and
are far apart.
PHASE CHANGES
A state is not permanent. Changes in pressure and temperature
alter mat ter- these are described as PHASE CHANGES.
MELTING is when matter changes from solid
to liquid. The melting point is the temperature
at which a solid melts. Heat causes solids to
melt by increasing the movement of particles.
As the particles gain more and more energy
from the heat, they move more and more
until they are no longer fixed in place.
Above 100°C, water is a vapor.
Between 0°C and 100°C, water is a liquid.
Below 0°C, water is a solid.
˚
100
˚
0
vapor
liquid
ice
FREEZING is when matter changes from liquid to solid. As
liquids cool down, the particles move less and less. At some point,
the motion of particles can’t overcome the attractive forces
between particles, and the liquid turns to solid. The temperature
at which a liquid freezes is called the FREEZING POINT.
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VAPORIZATION is when liquid turns to vapor. When sweat
disappears and dries up, it has vaporized or evaporated.
Evaporation happens slowly and only at the surface (individual
molecules get bumped out into the air). When water boils, it has
reached the temperature at which water turns from liquid to
vapor. Heat causes liquid particles to move around quickly. When
the particles are moving around fast enough to overcome all
attractive forces between particles, the liquid turns to vapor.
CONDENSATION is when vapor turns to liquid. When you
get a really cold drink, the air around the glass condenses and
forms little water droplets on the surface of the glass. When
water vapor in the air cools down and loses energy, the particles
start to slow down. When the particles slow down enough, the
attractive forces between particles cause the molecules in the
vapor to stick together, forming a liquid.
Sometimes, under extreme conditions, solids can change directly
to vapors, which is called SUBLIMATION. Dry ice, for example,
sublimates when the CO2 ice turns directly into CO2 vapor.
Vapors sometimes change directly into solids, which is called
DEPOSITION, like when frost appears on grass overnight.
n
tio
a
n
l im
tio
s u b ep o s i
d
melting
freezing
SOLID
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VAPOR
co
va p
nd
o ri
en
s at
io n
zat
io n
LIQUID
w CheckYour Knowledge
1. What is the positively charged particle in an atom?
2. Describe Thomson’s model of an atom.
3. I
f you turn eggs, flour, and milk into pancakes, what sort of
change have the ingredients undergone? If you make a smoothie
out of a banana, strawberries, and yogurt, what sort of change
have the ingredients undergone?
4. If you burn a piece of paper, is there more or less mass
than you started with?
5. Name some things that are not matter.
6. In terms of particles and volume, what is the difference
between a liquid and a vapor?
7. What happens at the vaporization point (boiling point) of a
substance?
8. Compare the molecular movements in a solid, vapor, and liquid.
9. W
hat is viscosity? Which has a higher viscosity: peanut butter
or ketchup?
10. D
efine vaporization and condensation. Give an example of each.
answers
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Check Your ANSWERS
1. A
proton
2. T
homson thought that electrons and protons were embedded
together, sort of like raisins in oatmeal-raisin cookies.
3. T
he ingredients in pancakes undergo a chemical change-the
ingredients have transformed into something else with new
chemical properties. For the smoothie, the ingredients have
undergone a physical change (the ingredients are the same, they
are just cut up into small pieces and blended together).
4. T
he same. Mass is conserved.
5. T
houghts, light, a vacuum
6. W
hile both can flow freely, the particles in a liquid stick together
and don’t completely separate. So the volume of a liquid is fixed
while the volume of a vapor is not fixed.
7. A
t the boiling point, a substance changes from a liquid to a gas.
8. M
olecules vibrate in a solid, but have fixed positions. Molecules in
a liquid flow freely, but they don’t completely separate because
they don't have enough energy to completely overcome the
attractive forces between molecules. Molecules in a gas move
freely and so quickly they can overcome all attractive forces
between molecules.
9. V
iscosity is the resistance to flow. Peanut butter resists flow more.
10. V
aporization is when liquid turns to vapor, like when sweat dries
up. Condensation is the opposite--when vapor turns to liquid, like
when water droplets form on the surface of a glass holding a
cold drink.
#5 has more than one correct answer.
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