Transcript Chapter 2 What Is Matter

Chapter 2
What Is Matter
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.
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.
Elements
An 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.
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.
Compounds
A 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.
The components of a compound combine in a
definite ration by mass. In this way, we can
write a formula to describe it.
H2O
Each compound has a set of characteristic
properties that identify it. These properties will
be different from those of the substances that
form it.
Compounds can be broken down
chemically into the substances that
formed it or into simpler compounds.
2H2O → 2H2 + O2
Atoms can combine chemically to form
molecules. Each molecule has a formula
which tells which elements and how many
atoms they contain.
Elements and compounds are
pure substances that have a
fixed composition and definite
properties.
Mixtures
A 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.
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.
Suspensions are considered heterogeneous
mixtures because different samples may
contain different compositions.
Gelatin, egg whites, and blood
plasma have such small
particles suspended that they
cannot be filtered and won’t
settle out. They are called an
colloid. Colloids exhibit the
Tyndall effect.
Bubbles and foam are gases that are leaving a
liquid but the coating of liquid around them holds
them on the surface.
Smoke is an aerosol.
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
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.
Properties of Matter
All matter has traits that can be
used to identify it. These traits
are called properties.
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.
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.
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.
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.
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
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.
Changes in Matter
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.
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.
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.
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