Chapter 2
2.1 Classifying Matter
Classifying Items
• People classify objects for different reasons.
Classifying food into groups, such as grains,
vegetables, and fruits help people plan meals that
maintain a healthy diet. Biologists classify
organisms into groups that have similar
characteristics, which makes the relationships
among organisms easier to see.
▫ Devise a classification system for the following items:
orange, lime, plum, apply, pear, rose, violet, daisy,
gold, and silver.
▫ Explain what criteria you used to place items into each
category of your classification system.
 (Teacher Note: Try classifying by syllables)
2.1 Classifying Matter
• Pure substances- Matter that always has exactly the same composition.
There is a fixed, uniform composition.
• Substances can be classified into two categories:
▫ Elements
 A substance that cannot be broken down into simpler substances.
There are just over 100 elements.
▫ Atom- The smallest particle of an element.
 An element has a fixed composition because it contains only one
type of atom.
• No two elements contain the same type of atom.
• Examples:
Pure Substances Con’t.
• Compounds
▫ A substance that is made from two or more simpler substances
and can be broken down into those simpler substances.
 The properties of a compound differ from those of the
substances from which it is made.
 A compound always contains two or more elements joined in a
fixed proportion.
Mixtures
• Mixtures tend to retain some of the
properties of their individual substances.
▫ The properties of a mixture can vary
because the composition of a mixture is
not fixed.
▫ Heterogeneous Mixtures - The parts of
the mixture are noticeably different
from one another. Examples: salads,
salsa
Mixtures
▫ Homogeneous Mixtures - The substances are so
evenly distributed that it is difficult to distinguish
one substance in the mixture from another.
Examples: steel, salt water
Solutions, Suspensions, and Colloids
Solutions, Suspensions, and Colloids
• Based on the size of its largest particles, a
mixture can be classified as a solution,
suspension, or colloid.
▫ Solution- Substances dissolve and form a
homogeneous mixture. Examples: tap water,
windshield-wiper fluid.
▫ Suspensions- Heterogeneous mixture that
separates into layers over time. Examples: sand
and water, oil and vinegar.
Solutions, Suspensions, & Colloids
• Colloids- Contains some particles that are intermediate
in size between the small particles of solutions and the
large particles of suspensions. Colloids will not separate
and cannot be filtered. However, colloids will scatter
light. (Tyndall Effect) Example: fog.
Tyndall Effect
2.2
Section 2: Physical Properties
QUESTIONS
QUESTIONS
• Let’s play 20 Questions!
Section 2.2 Physical Properties
• Physical property- Any characteristic of a
material that can be observed or measured
without changing the composition of the
substance in the material. Examples: viscosity,
conductivity, malleability, hardness, melting
point, boiling point, and density.
Physical Properties
• Viscosity- The tendency of a
liquid to keep from flowing. A
resistance to flowing. Example:
Honey has a high viscosity.
• Conductivity- A material’s ability
to allow heat to flow. Example:
Metal spoon over a stove.
▫ Materials with a high conductivity
are called conductors. They are
also a good conductor of
electricity as well. Wood is a poor
conductor.
Physical Properties
• Malleability- The ability of a solid to be
hammered into thin sheets without shattering.
Example: Most metals can be made into coins
or foil.
Because gold is both malleable and beautiful, it is often used to make
jewelry. These ancient gold medallions were made to form a necklace
Physical Properties
• Hardness- One way to compare harness of two
materials is to see which of the materials can
scratch the other. Stainless steel knife blades
can scratch copper. Diamond is the hardest
known material.
This Tlingit carver is
using an adze to
carve a canoe from
Western red cedar.
Red cedar is a
relatively soft wood
Physical Properties
• Melting Point- Temperature at which a substance changes
from a solid to a liquid. Example: Ice melts because the
melting point of water is 0ºC (32ºF).
• Boiling Point- Temperature at which a substance changes
from a liquid to a gas or vapor.
The table lists the
melting points and
boiling points for
several substances.
Physical Properties
• Density- Ratio of the mass of a substance to its
volume. This can be used to test the purity of a
substance. Examples: Silver has a density of
10.5 g/cm3.
Section 2: Physical Properties
• Density
▫ Describes the relationship between mass and
volume
 Density is the amount of matter in a given amount
of space, or volume
PING PONG
2 grams
GOLF
46 grams
Section 2: Physical Properties
• Solving for Density (d)
DENSITY = MASS
VOLUME
Densities of Common Substances
•
Density
can
help
identify
substances
3
SUBSTANCE
DENSITY (g/cm )
SUBSTANCE
DENSITY (g/cm3)
Helium (gas)
0.00001663
Zinc (solid)
7.13
Oxygen (gas)
0.001331
Silver (solid)
10.50
Water (liquid)
1.00
Lead (solid)
11.35
Pyrite (solid)
5.02
Mercury (liquid)
13.55
Section 2: Physical Properties
• Sample problem: What is the density of an
object whose mass is 25g and whose volume is
10 cm3?
• Step 1: Write the formula
DENSITY = MASS
VOLUME
Section 2: Physical Properties
• Sample problem: What is the density of an
object whose mass is 25g and whose volume is
10 cm3?
• Step 2: Identify the variables
25 g
10 cm3
Section 2: Physical Properties
• Sample problem: What is the density of an
object whose mass is 25g and whose volume is
10 cm3?
• Step 3: Put numbers in the equation
DENSITY =
25 g
10 cm3
Section 2: Physical Properties
• Sample problem: What is the density of an
object whose mass is 25g and whose volume is
10 cm3?
• Step 4: Solve and circle answer
DENSITY =
25 g
10 cm3
Density=
2.5 g/cm3
Using Physical Properties
• Physical properties are used to identify a
material, to choose a material for a specific
purpose, or to separate the substances in a
mixture.
▫ Using properties to identify materials




First, decide which properties to test
Second, do tests on the unknown sample
Third, compare results with a known sample
(This is used in crime scene investigations)
▫ Using properties to choose materials
 Properties determine which materials are chosen for
which uses. Example: shoelaces wouldn’t be made
from wood.
Using Physical Properties
▫ Using properties to
separate mixtures
 Filtration and distillation
are two common separation
methods.
 Filtration- A process that
separates materials based on
the size of their particles.
Example: brewing coffee
 Distillation- A process that
separates the substances in a
solution based on their
boiling points.
Example: Separate
freshwater from seawater.
Recognizing Physical Changes
• Physical change- Occurs when some of the
properties of a material change, but the
substances in the material remain the same.
Examples: cutting paper, melting butter.
Braiding hair and cutting hair are examples of physical changes. Braiding is a reversible
change. Cutting cannot be reversed
Physical & Chemical Properties
2.3 Chemical Properties
• Chemical property- Any ability to produce a
change on the composition of matter.
• Chemical properties can only be observed when
the substances in a sample of matter are
changing into different substances. Examples:
flammability and reactivity.
Chemical Properties
• Flammability- A material’s ability to burn in the
presence of oxygen. Examples: Anything that
can be used as a fuel. Wood, gas, paper.
• Reactivity- Describes how readily a substance
combines chemically with other substances.
Example: Iron with oxygen and water will form
rust. If you leave your bike out in the rain.
Recognizing a Chemical Change
• Chemical change- Occurs when a substance
reacts and form one or more new substances.
Examples: baking cakes, food digesting.
• Three common types of evidence for a
chemical change are a change in color,
production of a gas, and formation of a
precipitate.
Evidence for a Chemical Change
• Color Change
▫ Silver bracelets will darken.
▫ Matches burn and turn black.
▫ Copper roofs turn green.
Evidence for a Chemical Change
• Production of a gas
▫ Mixing vinegar with baking soda (carbon dioxide
gas)
▫ Cakes have gas bubbles in it
Gummy bear
Evidence for a Chemical Change
• Formation of a
precipitate
▫ Precipitate- Solids
form and separate
from a liquid
mixture
▫ Curdling of milkadding lemon juice
Physical & Chemical Properties Song
Is a Change Chemical or Physical?
• Sometimes gas bubbles or color change is not a chemical
change. You must ask yourself: Are different substances
present after the change takes place.
• When matter undergoes a chemical change, the composition
of the matter changes. When matter undergoes a physical
change, the composition of the matter remains the same.
A blacksmith uses a
hammer to shape a
horseshoe that has
been heated.
Although the color
of the iron
horseshoe changes,
no chemical change
is occurring