What are the 2 types of
pure substances?
Elements
Compounds
Elements are
the simplest
substances.
Elements CANNOT be separated into
simpler substances through any
chemical reaction or physical change.
If the substance
is an element,
the smallest
particle is an
ATOM.
What is sulfur’s
atomic number?
16
Sulfur
Elements are identified
by their atomic numbers.
(Number of protons)
Compounds are
formed when
elements are
chemically bonded
in a definite ratio.
Compounds CAN be separated into simpler
substances through chemical reactions.
How can you tell the difference
HINT: Every element is either
between elements and compounds if
abbreviated
withnames?
a single
you are told their
CAPITAL letter (H) or one
CAPITAL letter and one
lowercase letter (Li). Therefore,
when you are trying to decide if
a substance is an element or
compound – count the capital
letters!
Elements will be
found directly on
the PERIODIC TABLE
OF THE ELEMENTS
while compounds
are NOT directly
found on the table,
but are two or more
elements
combined. (Ex: H2O
– H and O.)
Decide if the substances listed on your
notes are elements or compounds.
compound
compound
compound
element
compound
element
Hint: Only two of the substances are elements.
Iron and Sulfur
mixed together.
Mixtures are formed when
substance are placed together
which will not chemically react.
Mixtures CAN be separated based on the physical
properties of the substances in the mixture.
There are two main
categories of mixtures.
Heterogeneous Mixtures
Homogeneous Mixtures
The substances within the mixture
are distinct and easily identified.
The substances within the
mixture are blended
evenly together.
Mixtures are NOT formed with any kind of
definite ratio. While brass is a mixture of
copper and zinc, there is not an exact recipe
and different manufacturers will use a
slightly different percentage of each metal.
Brass
Copper
Zinc
While Kool-Aid® is a mixture
of
,
and
, the amount of
sugar can be adjusted to
taste. Changing the amount
of sugar does not change the
identity of the mixture.
There is no definite ratio.
Notice that this also shows that
substances
when they are in a mixture!
is sweet because
is sweet!
Steel is a mixture of iron and
other elements.
is
magnetic because
is
magnetic. It retains its
properties inside the mixture.
Solutions
Solutions one of the most common forms of
mixtures. They are created when substances are
evenly mixed together.
Solution = Homogeneous Mixture
Aqueous solutions
are formed with
solutes are
dissolved in water
Alloys are formed
when metals are
evenly mixed
together.
Gaseous solutions,
like air, formed
when gases mix
together.
Important Fact: An alloy is made
when metals are mixed together.
The metals are melted together
and mixed. They can be separated
by melting the alloy. When a solid
has melted completely into a
liquid, we say that it is molten.
Is melting a physical or chemical change?
Melting is a physical change. This means that
alloys are NOT a new substance. They are
simply a mixture of substances.
Common Alloys
Steel
Brass
Bronze
(Iron and Nickel
Alloy)
(Copper and
Zinc Alloy)
(Copper and
Tin Alloy)
Let’s take a look at a few
different ways to separate
mixtures:
• Sifted/filtered
• Magnetism
• Distillation
• Separatory Funnel (density)
While volume, sometimes simply referred to as size
and shape, is related to the size of a sample and it can
be used to separate a substance from a heterogeneous
mixture. If one substance is in larger pieces than the
other, the larger substance can be sifted or filtered
from the mixture.
Some elements can be separated from
heterogeneous mixtures based on the physical
property of magnetism. In particular these
elements are iron, cobalt, and nickel. Together
these elements are known as the Iron Triad.
Distillation is a process that
is used to separate a liquid
from a homogeneous
mixture based on
differences in boiling point.
1. Water is evaporated from
the solution
2. The evaporated water is
cooled and condenses back
into a liquid
3. The pure, distilled water
is collected.
Distillation
Distillation can also
be used to separate
two liquids which
have been dissolved
together. Liquids
that can be evenly
mixed together are
known as miscible
liquids. Miscible
liquids are either
both polar or both
nonpolar.
Oil and water are immiscible because one
is polar and the other in nonpolar.
Based on this
picture, which
liquid is more
dense: oil or
water?
Oil
Water
Immiscible liquids can
be separated very
easily using a device
known as a separatory
funnel. Notice that
this device also
separates
heterogeneous
mixtures based on the
property of density.