Chapter 2 What Is Matter

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Chapter 2What Is Matter
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When we study matter, we are studying chemistry.
It is the study of what things are made of, what
their properties are, and how they change and
interact.
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Each object around you is matter. Matter is
everything that is anything. Matter is defined
as anything that has volume (takes up space) and
mass.
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ElementsAn element is a pure substance that
cannot be separated into simpler substances by
physical or chemical means. An element is
considered a pure substance meaning that it is
only made of one kind of particle. In fact,
elements are made of only one type of atom.
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In chemistry, elements are designated by a one or
two letter symbol. Each of the more than 110
elements that we know has properties that are
different than the rest.
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CompoundsA chemical compound is a pure substance
that is made of two or more elements that are
chemically combined. Because of this definition,
we know that the substances that make up a
compound change into a new identity and cannot be
separated physically.
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The components of a compound combine in a
definite ration by mass. In this way, we can
write a formula to describe it.H2OEach
compound has a set of characteristic properties
that identify it. These properties will be
different from those of the substances that form
it.
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Compounds can be broken down chemically into the
substances that formed it or into simpler
compounds.2H2O ? 2H2 O2
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Atoms can combine chemically to form molecules.
Each molecule has a formula which tells which
elements and how many atoms they contain.
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Elements and compounds are pure substances that
have a fixed composition and definite properties.
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MixturesA pizza is a good example of a mixture.
A mixture is a combination of two or more
substances that are not chemically combined.
Because the substances are not chemically
combined, each substance retains its identity and
can be physically separated back out of the
mixture.The components of a mixture may be
mixed in any ratio and still be considered a
mixture.
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If a mixture contains large particles dispersed
in a liquid or a gas that will settle out, it is
classified as a suspension. If the particles of
a suspension are not stirred constantly, they
will settle out. Particles of a suspension can
also be filtered out. The particles are large
enough to be caught in filters. Other examples
of suspensions would be dirty water, dust storms,
and Italian dressing.
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Suspensions are considered heterogeneous mixtures
because different samples may contain different
compositions.
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Gelatin, egg whites, and blood plasma have such
small particles suspended that they cannot be
filtered and wont settle out. They are called
an colloid. Colloids exhibit the Tyndall effect.
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Bubbles and foam are gases that are leaving a
liquid but the coating of liquid around them
holds them on the surface.
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Smoke is an aerosol.
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A solution is a mixture that appears to be a
single substance but is actually two substances
distributed in each other in a single phase. We
often call a solution a homogeneous
mixture.Saltwater is a common solution. Salt
is very soluble in water. If a substance will
not dissolve, it is considered insoluble. The
salt is dissolved so it is considered the solute
and the water does the dissolving so it is
considered the solvent.If two liquids dissolve
into one another, they are said to be miscible.
If the liquids are like oil and water, they are
considered immiscible
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Actually, solutions do not have to be a solid
dissolved in a liquid. Since there are three
common phases of matter, there are nine possible
types of solutions. Such as Air is a gas
dissolved in a gas. Soft drinks are a gas
dissolved in a liquid. Humid air is a liquid
dissolved in a gas. Antifreeze is a liquid
dissolved in a liquid. Saltwater is a solid
dissolved in a liquid. And brass is a solid
dissolved in a solid. Solid solutions are called
alloys.
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Properties of Matter
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All matter has traits that can be used to
identify it. These traits are called properties.
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Physical properties are traits that can be
determined without changing the identity of the
matter. We constantly rely on physical
properties to tell us about the world around us.
Physical properties include dimensions, thermal
conductivity, state, malleability, ductility,
expansion-contraction, solubility, color, and
density.
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Density is a very important physical property
since it can be used to determine the identity of
substances. Density is calculated by dividing
the mass of an object by its volume. The units
are then stated as grams per cubic centimeter.
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The physical properties of matter often help
determine its uses. Copper is useful for wires,
antifreeze is useful in cars, and aluminum is
useful for building airplanes.
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Chemical Properties

• Chemical properties are those properties that are
  based on the ability of a substance to change
  into a different substance. These might include
  flammability, reactivity to acids and bases,
  reactivity with water, and oxidation.

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Indicators of Chemical Reactions Include

• Changes in temperature
• Evolution of a gas
• Formation of a precipitate
• Emission of light
• Generation of electric current
• Sounds
• Changes in color

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Properties such as color, solubility and density
which are useful in identifying matter are called
characteristic properties. They may be chemical
or physical in nature.
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Changes in Matter
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Physical changes are changes that affect one or
more physical properties. These might include
melting, evaporating, crushing, bending, mixing,
and dissolving. One should remember that since a
physical change only affects physical properties,
it can be undone. One should remember that
dissolving is a physical change.
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A mixture is a combination of two or more
substances that are not chemically combined.
Because the substances are not chemically
combined, each substance retains its identity and
can be physically separated back out of the
mixture.
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A chemical change is one that occurs when a
substance changes into an entirely new substance
with new properties. These would include baking
a cake, the souring of milk, the burning of fuel,
rusting, and the fizzing away of an alkaseltzer.
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There is a definite set of clues that a chemical
change is taking place

• temperature change
• evolution of a gas
• formation of a precipitate (new solid)
• production of light
• production of electric current
• production of sound
• color change