B.3 – B.4
In which you will learn about:
•Pure substances
•Mixtures
•Atoms, molecules, compounds, elements
B.3 MIXTURES AND SOLUTIONS
Types of Matter
• Mixture - Variable combination of 2 or more
pure substances.
Heterogeneous –
visibly separate materials
Homogeneous (solution)–
Same throughout
Types of heterogeneous mixtures
• Suspension: solid particles are large enough to
settle out or can be separated by using filtration
– Ex: water and coffee grounds
– Ex: water and pepper flakes
• Colloid: particles smaller than a suspension (don’t
settle out) and may cause water to appear cloudy
(but can’t see individual particles)
– Ex: whole or low-fat milk
• Tyndall Effect: exhibited by both suspensions and
colloids—when light is scattered by particles in a
mixture
Homogeneous Mixtures
• Particles that are far smaller than colloidal
particles are often dissolved into a mixture
• Homogeneous mixtures (solutions) do NOT
exhibit the Tyndall Effect
• Solvent: the dissolving agent
• Solute: the dissolved substance
Mixture Comparison
Mixture Type
Appearance
Particles Settle
Out?
Tyndall Effect?
Suspension
Large particles
suspended in
solvent, visible to
the eye
Yes
Yes
Colloid
Medium particles
not visible to the
eye, but mixture
appears cloudy
No
Yes
Solution
Small particles,
invisible to the eye
and microscope,
and mixture
appears clear
No
No
B.4 Particulate View of Water
Macroscopic v. Microscopic
• In chemistry, we make observations in the lab
on the macroscopic level
• We then explain our observations at the
microscopic level, or particulate level. This
explains the big world stuff based on the
interactions of atoms and molecules.
Pure Substance = ONE material
• CHEMICAL ELEMENT
-
– pure substances that cannot be decomposed by ordinary
means to other substances.
Aluminum
Sodium
Bromine
The Language of Chemistry
• The elements, their
names, and symbols
are given on the
PERIODIC TABLE
• How many elements
are there?
117 elements have been identified
• 82 elements occur naturally on Earth
Examples: gold, aluminum, lead, oxygen, carbon
•35 elements have been created by scientists
Examples: technetium, americium, seaborgium
The Periodic Table
Dmitri Mendeleev (1834 - 1907)
Glenn Seaborg
(1912-1999)
• Discovered 8
new elements.
• Only living
person for
whom an
element was
named.
• An ATOM is the smallest particle of an
element that has the chemical properties of
the element.
Copper
atoms on
silica
surface.
Distance across = 1.8 nanometer (1.8 x 10-9 m)
The Atom
An atom consists of a
• nucleus
– (of protons and neutrons)
• electrons in space about the nucleus.
Electron cloud
Nucleus
CHEMICAL COMPOUNDS are
pure substances composed of atoms and
so can be decomposed to those atoms.
The red compound is composed
of
• nickel (Ni) (silver)
• carbon (C) (black)
• hydrogen (H) (white)
• oxygen (O) (red)
• nitrogen (N) (blue)
Compounds
– composed of 2 or
more elements in a
fixed ratio
– properties differ from
those of individual
elements
– EX: table salt (NaCl) –
NOT reactive like Na,
and NOT poisonous
like Cl2
MOLECULE
A
is any two or more atoms
chemically bonded together. MOST molecules are
compounds, like those shown below.
Composition of molecules is given
by a MOLECULAR FORMULA
H2O
C8H10N4O2 - caffeine
BUT SOME ELEMENTS EXIST AS
DIATOMIC MOLECULES
MEMORIZE:
BrINClHOF
These elements
only exist as
PAIRS. Note that
when they combine
to make
compounds, they
are no longer
elements so they
are no longer in
pairs!
Matter Flowchart – To Sum
it All Up
MATTER
yes
MIXTURE
yes
PURE SUBSTANCE
Is the composition
uniform?
Homogeneous
Mixture
(solution)
Colloids
no
Can it be physically
separated?
no
Heterogeneous
Mixture
yes
Can it be chemically
decomposed?
Compound
Suspensions
Element
no
HOMEWORK QUESTIONS
• 1) Match each description below with the
following microscopic pictures. More than one
picture may fit each description. A picture may
be used more than once or not used at all.
a) A gaseous compound
b) A mixture of two
gaseous elements
c) A solid element
d) A mixture of a gaseous
element and a gaseous
compound
HOMEWORK CONT’D
• 2) How are heterogeneous and homogeneous
mixtures different?
• 3) Identify each of the following materials as a
solution, a suspension, or a colloid.
– A medicine accompanied by instructions to “shake
before using.”
– Italian salad dressing
– Mayonnaise
– A cola soft drink
– An oil-based paint
– milk
MORE HOMEWORK
• 4)You notice beams of light passing into a
darkened room through the blinds on a window.
Does this demonstrate that air in the room is a
solution, a suspension, or a colloid? Explain.
• 5) Suppose you have a clear, red liquid mixture. A
beam of light is observed as it passes through the
mixture. Over a period of time, no particles settle
to the bottom of the container. Classify this
mixture as a solution, a colloid, or a suspension
and provide evidence to justify your choice.
OMG, EVEN MORE HW
• 6) Define the term pure substance and give two
examples.
• 7) Classify each of the following substances as an
element or a compound:
–
–
–
–
–
–
–
CO
Co
HCl
Mg
NaHCO3
NO
I2