Download Chemistry: Classification of Matter

CHEMISTRY: CHANGE &
MATTER
Chemistry
Chapter 2
CHEMISTRY
Chemistry is the study of matter and changes
in matter.
Matter is anything that occupies space and
has mass.
Matter is classified according to different
physical properties.
CLASSIFYING MATTER
Matter can be classified according to it’s
physical state at room temperature.
Matter is classified as: gas, liquid or solid.
Shape
Volume
Gas
No definite
shape
No definite
volume
Liquid
No definite
shape
Definite
volume
Solid
Definite shape Definite
volume
PHYSICAL CHANGES IN MATTER
Three types of STATE changes are possible:
Between solid and liquid
Between liquid and gas
Between solid and gas
Each state change occurs at a specific
temperature for a given material so is a
physical property.
Ex. Ice melts at 0° Celsius
CHANGES BETWEEN SOLID AND LIQUID
Melting is the change from solid to liquid
in which energy is added.
Freezing is the change from liquid to
solid in which energy is released.
Both processes occur at the same
temperature called the melting point,
freezing point or temperature of fusion.
CHANGES BETWEEN LIQUID AND GAS
Evaporation or vaporization are both
terms used to describe the change from
liquid to gas in which energy is added.
Condensation is the term used when a
gas becomes liquid and energy is
released.
The temperature at which gas bubbles
form in a liquid and the liquid becomes a
gas is the boiling point.
CHANGES BETWEEN SOLID AND GAS
Sublimation is the term used when a
solid changes directly into a gas.
When a gas turns directly into a solid the
term condensation is applied.
The sublimation point is the temperature
at which this occurs for a given
substance.
Ex. CO 2
CO 2 TEMPERATURE PRESSURE PHASE
DIAGRAM
PURE SUBSTANCES
Any solid, liquid or gas can be
classified as either a pure
substance or a mixture.
Pure substances have constant
composition, and the same
properties for each physical state.
MIXTURES
Mixtures have varying proportions of
components and varying physical
properties.
Mixtures can be separated into pure
substances by physical means
(evaporation, distillation, filtering).
PHYSICAL AND CHEMICAL CHANGES
A physical change causes no change in
the basic nature or composition of pure
substances.
Ex. Melting ice
A chemical change causes the formation
of new material with different properties.
Ex. Burning a piece of paper
PHYSICAL VS. CHEMICAL CHANGES
In a physical change, a change in appearance
is the result of a new set of conditions
imposed on the same material.
If the old conditions are restored the original
appearance should return.
In a chemical change, a change in appearance
is the result of the formation of new material,
and it will not return to the original
appearance.
CHEMICAL REACTIONS
 A chemical reaction is a change in which the
composition of one or more substances is
altered.
 Evidence of a chemical reaction includes:
 Change in physical properties of a substance
 Formation of a gas or new liquid layer
 Formation of a precipitate ( insoluble solid)
 Change in color (most of the time)
Evidence of either a chemical or physical change
can be a change in temperature
EXAMPLES
Are the following physical or chemical
changes?
Pork is sliced
The sugar in grain ferments into alcohol and
small bubbles form in the liquid.
Sugar dissolves in hot water.
Sugar is heated to a brownish color and non
crystalline texture.
Oxygen gas is compressed and liquefied.
IDENTIFYING A PURE SUBSTANCES
Only properties that are independent of the
amount of a substance present can be used to
identify if it is pure.
The physical properties that can be used are:
Boiling point, melting point, color, and
physical state at room temperature
Odor, electrical conductivity, solubility (ability
to dissolve in a liquid) and crystalline form
MIXTURES
Mixture are physical combinations of two
or more materials in no fixed proportion.
The components of a mixture are not
chemically combined and therefore can
be separated by physical means.
Mixtures have no fixed ratio and
therefore the physical properties of any
mixture will vary with it’s composition.
CHEMICAL PROPERTIES USED FOR
IDENTIFICATION
The chemical properties that can be
used to identify a pure substance are
based on chemical reactions.
They include ways the substance reacts
with other substances, such as:
Flammability
Oxidation
Reaction to acids
PURE SUBSTANCES
Pure substances can be divided into
compounds and elements.
Compounds can be broken down into
simpler substances by chemical
reactions.
Elements are substances that can
not be broken down any further.
ELEMENTS
Elements are the building blocks from
which all matter is made.
There are 114 known elements.
Elements are classified as metal or
nonmetal.
The metals are located on the left side of
the periodic table, non-metals on the
right.
PERIODIC TABLE
All elements have a one, two or three
letter symbol.
Elements are arranged on the periodic
table according to atomic number and
group properties.
METALS VS. NONMETALS
Metals are shiny, conduct electricity
and are malleable.
Nonmetals are not shiny, do not
conduct electricity and are brittle.
Nonmetals are also often gases at
room temperature.
COMPOUNDS
Compounds form when two or more
elements chemically combine (react) to
form a new material with a fixed
chemical composition and a different set
of properties.
Law of definite composition: A compound
always contains its component elements
in a fixed ratio by weight.
BUILDING BLOCKS OF CHEMISTRY
The building blocks of chemistry are
atoms.
Atoms are very small, spherical units that
fit together to make up each element.
Every atom in a particular element is the
same and the atoms are unique to that
element.
The difference in size and structure of the
atoms accounts for the different
properties of elements.
CHEMICAL LANGUAGE
Words that represent elements are called
atomic symbols.
 Ex. Sodium = Na
Words that represent compounds are called
chemical formulas.
 Ex. Sodium chloride = NaCl
Words that represent a chemical reaction are
called a chemical equation.
 Ex. Na + Cl > NaCl
CHEMICAL EQUATIONS
Chemical reactions are represented by
chemical equations.
The elements that combine or react are
called the reactants and are on the left
side of the chemical equation.
The products are the new materials
formed and are on the right side of the
chemical equation.
An arrow is drawn in the middle to
symbolize “yields.”
 Ex. Na + Cl > NaCl
CHEMICAL FORMULAS
In chemistry, when elements combine they
are called molecules or compounds and
are represented by chemical formulas.
The symbols of combined elements are
written w/o any space between them in a
chemical formula.
The formula tells you the elements present
and the ratio of those elements.