Unit 1
Elements, Compounds, and Mixtures
Mixtures, elements,
compounds
Scientists like to classify things.
One way that scientists classify matter
is by its composition.
Ultimately, all matter can be classified
as mixtures, elements and compounds.
What is an element?
An element is a pure substance that cannot be
separated into simpler substances by physical or
chemical means.
A pure substance is a substance in which there is
only one type of particle.
The particles of pure substances are exactly alike
no matter their size or where they are found.
Element
Element
Substance that contains only 1 type of
atom
Examples: H, He, O, B … anything
from periodic table--> that’s why it’s
called the periodic table of elements
90 different elements found in nature, the others are man-made
Every element has a unique
set of properties
An element is identified by its unique set
of properties.
These properties can be physical or
chemical properties.
These properties do not depend on the
amount of the element present.
Properties of Elements
Properties are not
unique to the
element.
Ex. He & Kr are both
gases but have very
different densities.
He is lighter (less
dense) than air
while Kr is heavier
(more dense) than
air
Elements are
classified by their
properties
Elements are classified into
groups according to their
similar properties.
For example, elements that are
shiny are classified into a group
called metals.
You can predict some of the
properties of an unfamiliar
element by knowing the
category to which it belongs.
The Three Major Categories of Elements
Metals
Non-metals
Metalloids



Metals are elements that are shiny and are good conductors of thermal
energy and electric current. They are malleable and ductile.
Non-metals are elements that are not shiny, poor conductors of thermal
energy and electric current. They tend to be brittle and non-malleable.
Metalloids are also called semi-conductors. These elements have the
properties of metals and non-metals.
Why isn’t it a good idea
to classify matter by its
phases?
Because one kind of
substance can exist
in more than one
phase – such as
H20. And matter
changes phases
rather easily.
Why isn’t matter classified
according to its physical
characteristics, such as
color?
Scientists wouldn’t
find it very useful to
group gold,
sunflowers, and the
sun together.
Atoms
The basic component of all
matter.
The atom is the smallest
particle of an element that
has all of the chemical
properties of that element.
Atoms consist of a nucleus
of protons and neutrons
surrounded by electrons.
http://www.ktfsplit.hr/glossary/image/atom.gif
Elements
A substance
consisting of a
single type of
atom.
It cannot be
broken down
into different
kinds of matter. http://www.rentrain.com/r
esources/Helium%20Safet
y.jpg
http://www.reachoutmichigan.org/
funexperiments/agesubject/lesson
s/handouts/helium.GIF
Molecules
Compound of two
or more atoms,
the smallest unit of
chemical
compounds.
The smallest
particle of a
substance that
has all of the
physical and
chemical
properties of that
substance.
http://www.awwu.
biz
Compounds
Most elements are not found alone in nature, but rather
combined with other elements.
A compound is a pure substance composed of two or more
elements that are chemically combined.
To be chemically combined, the elements in the compound
need to have reacted with one another.
Most substances you encounter are compounds!
Every compound has a unique set of
properties
Each compound has a unique set of properties that allows you
to distinguish it from other compounds.
A compound has different properties from the elements
that form it.
For example, table salt (NaCl), is made up of sodium and
chloride, two dangerous elements on their own!
Observe how sodium and chlorine react to form salt!
sodium
chloride
+
table salt
=
Properties: compounds vs
elements
Properties of the compound can be very
different from the properties of the
individual elements that make up the
compound
Na is a silvery, white metal that is
explosive when combined with oxygen
Cl is a poisonous greenish-yellowish gas
NaCl is a white solid that is great on
french fries.
Compounds can be broken
down into simpler substances
Some compounds can be broken down
into elements through chemical
changes.
Some compounds are simply broken
down into simpler compounds through
chemical changes.
You cannot break a compound down
through a physical change!!!
Breaking down compounds
Usually energy is
necessary for a
chemical change to
happen
Apply heat
Apply electric current
Compounds in your
world
Compounds are found in nature and industry.
Proteins are compounds that are found in all living
things. They are all composed of nitrogen and
other elements.
Carbon dioxide is another important compound.
In industry, compounds are often synthetically
created.
Combinations of Elements:
Compounds
A substance formed
from two or more
elements, with a fixed
ratio determining the
composition.
The elements lose
their individual
chemical properties
and the compound
has new properties.
http://www.awwu.
biz
Formulas
The formula which
identifies the atoms
and the number of
each kind in the
molecules of a
compound.
The number and types
of atoms in a molecule.
Glucose
C6H12O6
Formulas
6C6H12O6
Elements in the compound:
Carbon
Hydrogen
Oxygen
Formulas:
Subscripts
6C6H12O6
# of atoms of each element in a molecule of the
compound:
Carbon - 6
Hydrogen - 12
Oxygen - 6
Formulas:
Coefficients
6C6H12O6
# of molecules:
6 molecules of glucose
Mixtures
A mixture is a combination of two or more
substances that are not chemically combined.
Two or more substances together form a mixture
if they do not react to form a compound.
Substances in a mixture retain their identity, they
do not change into something else.
Mixtures can be physically separated through
physical change. Ex: picking the pecans out of
pecan pie, boiling salt water to remove the salt.
Combinations of Elements:
Mixtures
A substance consisting
of two or more
substances mixed
together.
Mixtures can usually be
separated by
mechanical means.
Two or more substances
mixed together in such a
way that each remains
unchanged.
http://www.seelecttea.com/
The Big Picture
Notice the two types of
mixtures,
heterogeneous and
homogenous.
Suspensions, Solutions
and Colloids are all
considered mixtures.
This is an important
chart because it shows
you visually how
mixtures are
categorized.
Common Techniques For Separating Mixtures
Distillation
Magnet
Centrifuge
Multiple Steps
 Distillation is the process of separating a
mixture through boiling.
 Magnets can be used to separate a mixture by
attracting the substance that is magnetic.
 A centrifuge is a machine that separates a
mixture according to the substances different
densities.
 Some mixtures can only be separated by
multiple different steps.
Solutions
A solution is a mixture that appears to be a single substance
but is composed of particles of two or more substances that
are distributed evenly amongst each other.
Solutions are described as homogenous mixtures because
they have the appearance of a single substance.
When substances are dissolved, the substance being
dissolved is known as the solute and the substance into
which it is dissolved is known as the solvent.
Soluble or insoluble?
We think of solutions as liquids, but they can also be gases
(air) or solids (steel).
Solute vs solvent
Solute: the substance
that dissolves in the
solvent, must be soluble
in the solvent.
Solvent: the substance
in which the solute
dissolves
Ex: sweetened tea
Solute is the sugar
Solvent is the tea
alloys
Not all solutions are liquid
Alloy are solid solutions of metals or
nonmetals dissolved in metals
Steel is an alloy of nonmetal carbon
dissolved in iron
An alloy is a homogeneous hybrid of
two or more elements, at least one of
which is a metal, and where the
resulting material has metallic
properties.
The resulting metallic substance
usually has different properties
(sometimes substantially different) from
those of its components.
More about solutions…
Particles in a solution are extremely
small.
This means that you may not see a
cloudy mixture, it may look as if it is
all one substance. That is because the
particles are so small.
Heterogeneous Mixture
Heterogeneous mixture
Least mixed mixture does not appear to
be the same throughout. Parts are easy
to recognize and separate.
Examples: granite, tacos, bowl of cereal,
big Mac, Italian salad dressing, concrete,
crunchy peanut butter, sandwich….
Homogeneous Mixture
Homogeneous mixture
Well-mixed, appears to be the same
throughout. Particles are small, not
easily recognizable and do not settle
when the mixture is allowed to stand.
Examples: glass, stainless steel, sugar
dissolved in water…
Concentration and
Solubility
A measure of the amount
of solute dissolved in the
solvent is known as the
concentration of a
substance.
Knowing the exact
concentration in a
solution is very important
in chemistry and in life.
Dilute or concentrated?
Expressed in grams per
mL.
Solubility refers to
the amount of solute
needed to make a
saturated solution
using a given amount
of solvent. Ex: sugar
in lemonade
Expressed in grams
per 100 mL.
Concentration and
Solubility
Concentration
EX: “from
concentrate”
Solubility
EX: “sweet, sweet
lemonade”
solubility
If you add too much
sugar to a glass of iced
tea, not all of the sugar
dissolves
The maximum amount
of sugar that can be
dissolved depends on
the solubility of the
sugar at a certain
temperature
temperature
Most solids are more soluble
in liquids at higher
temperatures
Gases become less soluble in
liquids as the temperature is
raised
Soft drinks go flat faster when
warm. The gas that is
dissolved in the soft drink
cannot stay dissolved when
the temperature increases.
Dissolving solids faster
in liquids
Mixing or stirringcauses solute to
separate from one
another
Heating- causes solute
to move more quickly
Crushing- increases the
amount of contact the
solute has with the
solvent
What affects how quickly
solids dissolve in liquids?
Most of the solutions that you are familiar with
are of a solid dissolved in a liquid.
Several factors affect how quickly the solute
will dissolve.



Mixing – stir or shake to make particles spread out
more evenly and to speed up dissolving.
Heating – this causes particles to move more quickly
thus speeding up the process of dissolving.
Crushing – crushing or grinding up the solute
increases the amount of contact b/t the solute or
solvent and increase how quickly the dissolving takes
place.
Suspensions
A suspension is a mixture in which particles of the
material are dispersed throughout a liquid or gas
but are large enough that they settle out.
The particles in a suspension are insoluble, so they
settle out.
Suspensions are called heterogeneous mixtures
b/c the different components are easily seen.
Ex: snow globe, muddy water, salad dressing
Suspensions can be separated by passing them
through a filter.
Colloids
A colloid is a mixture that has the properties of
both a solution and a suspension.
A colloid is a mixture in which the particles are
dispersed throughout but are not heavy enough to
settle out.
Examples: Jello, milk, fog, mayonnaise, stick
deodorant, whipped cream
colloids
The particles in a colloid are much smaller
than the particles in a suspension.
Particles are large enough to scatter light.
Colloid can not be separated by filtration
Particles are so small they can pass through
a filter
One Element
The Same Element
(Gas)
(Solid)
Another element
This one likes to go
round in pairs as a gas
(molecules)
A mixture of two
elements
This is not a mixture,
it is a COMPOUND
of two different
elements
This is just a
mixture of two
elements
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Element
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Element
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Mixture
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Mixture
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Compound
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
Compound
Element, Compound
or Mixture ?
Element, Compound
or Mixture ?
A mixture of a
compound and
an element
What do we call these
things?
An Atom
3 Atoms
What do we call these
things?
6 Atoms which
happen to be of 3
different elements
What do we call these
things?
A Molecule
Yes, it also happens to be
2 atoms joined together
but we don’t call it “2
atoms joined together”
we say it is one molecule
What do we call these
things?
A Molecule of a
compound
2 molecules of a
compound
What about when all
the atoms are stuck
together like in a
solid element?
This is just a load of
atoms in a solid
element, it is not a
big molecule
Finally, just to confuse you even more,
science teachers like talking about
Particles
Particle is just a fancy name for individual
things. These individual things could be
atoms, molecules, lumps of soil, grains of
sand, bits of metal. It doesn’t matter
because particle is just a general word
which is used when we don’t (or can’t) want
to be exact about the type of things being
described.
A good example of when science
teachers use the word particle is when
talking about air.
Air is a mixture of elements such as
oxygen, argon and nitrogen mixed with
compounds such as carbon dioxide
Some of the elements in air go around
as single atoms (such as argon).
Or as molecules such as oxygen.
Compounds go around as molecules.
That’s why we talk about particles
because it saves the bother of
describing exactly what sort of things
they are.
Classifying Matter According to
its Composition: Compounds
Matter
Pure Substances
Elements
Compounds
Compounds – substance
composed of two or more
elements in fixed proportions,
i.e. H2O & CO2
Mixtures
Classifying Matter According to its
Composition: Elements,
Compounds, & Mixtures
Matter
Pure Substances
Elements
Compounds
Mixtures
Homogeneous
Heterogeneous
Classifying Matter According
to its Composition: Mixtures
Matter
Pure Substances
Elements
Compounds
Mixtures
Homogeneous
Heterogeneous
Heterogeneous Mixtures – oil & water, sand & gravel,
composition is not uniform. 2 separate samples
would yield varying amounts of the components
Homogeneous – Sugar dissolved in water. Uniform
composition. 2 separate samples would yield the
same ratio of components
Passing an electric current
through a certain substance
produces oxygen and sulfur.
This substance cannot be a(n)




compound.
mixture.
element.
solution
Which of the following is
a mixture?




sodium chloride
carbon dioxide
sucrose
air