Classification of Matter
Concept One: Homogeneous Substances
• A homogeneous substances looks to a person’s eyes as if it is
uniform throughout, appearing to be of one substance.
Concept Two: Heterogeneous Substances
• A heterogeneous substances looks to a person’s eyes
as if it is made up of two or more parts.
Concept Three: A Pure Substance
• A pure substance has properties that are fixed and exact which
do NOT change over time or from sample to sample of the
same substance.
• Sodium is soft, silvery in color, melts at
97.8 celsius, conducts electricity well and
explodes when placed in water.
Concept Four: Impure Substances
• An impure substance has variable (changing) properties from
sample to sample of the substance. The properties of an
impure substance are NOT FIXED (melting point/boiling point
varies, density varies, color varies etc.)
• The color of a tea solution can vary as can its strength. Even though a
substance LOOKS uniform throughout (homogeneous), it is NOT
NECESSARILY PURE!
Heating and Cooling Curves of Pure and Impure Substances
• The heating/cooling curve of a pure substance always has
plateaus or flat sections where it melts or boils because it
melts/boils at fixed temperatures whereas impure substances
melt/boil at variable temperatures.
Every Pure Substance has Unique, Fixed Melting
and Boiling Points
Pure substances are distinguished by their physical and
chemical properties
• Physical properties are properties
that substances have by
themselves (Like color, density,
electrical conductivity, melting
point, boiling point)
• Chemical properties are properties
that substances have when they
are combined with other
substances (Like fizzing with an
acid, solubility with water etc.)
Physical and Chemical Changes
•
•
A physical change is a change in which
a substance retains its identity
(becomes itself in another form) and
usually can be easily reversed.
A chemical change (reaction) is a
change in which new substances are
formed with different physical and
chemical properties from the original
substance(s).
A Classification System For Matter
Mixtures
• Mixtures are impure substances with variable properties.
• The four common types of mixtures are mechanical mixtures,
suspensions, colloids and solutions.
Mechanical mixtures are impure, heterogeneous
substances made up of different parts visible to the
unaided eye.
The Tyndall Effect
• When light passing through a substance is visible from the side
(due to particles big enough to scatter the light), this is called
the Tyndall Effect.
• The Tyndall Effect is used to classify mixtures
The Tyndall Effect is only observed when the
particles in suspension are large enough to scatter
light sideways
Filtration
• Filtration removes large suspended particles.
• Being able to remove parts of a mixture by filtration is a way to
distinguish different kinds of mixtures.
Distillation
• A Liquid mixture can be heated and the different liquids in the
mixture will boil off as vapours at different temperatures, leaving
dissolved solids as a residue when all the liquids have been
vaporized.
Commercial Distillation
• Distillation is a
technique used to
separate components
of mixtures in many
commercial operations
like making brandies
or whiskeys or, in
separating crude oil
into its parts.
Chromatography
• Components of mixtures can be separated by chromatography
in which a sample is placed in a solvent which dissolves and
moves mixture parts at different rates, separating them.
Ink Chromatography
Solutions are impure homogeneous mixtures that
are usually clear (may be colored).
• Solutions do NOT show the Tyndall
Effect because their particles are too
small.
• Solutions may be separated with
distillation and with chromatography.
• Solutions can NOT be separated by
filtration.
Alloys are solutions of two or more metals
• Brass is an alloy of zinc and copper.
• Bronze is an alloy of tin and copper.
• Stainless steel is an alloy of iron, carbon, chromium or nickel.
Colloids – Can’t be Separated by Filtration
• Colloids are impure and homogeneous. They can be clear,
cloudy or opaque mixtures that have large enough particles to
show the Tyndall Effect.
Suspensions
• Suspensions are impure heterogeneous/homogeneous
mixtures whose parts can be separated by filtration.
• On standing, parts of suspensions often settle to the bottom
because their particles are large enough to be pulled down by
gravity.
Centrifuges and Suspensions
• Centrifuges spinning at high speeds will separate
suspensions.
Classification of Impure (Mixture) and Pure
Substances
Pure Substances: Elements
• An element is a pure homogeneous substance that can NOT be
broken down into a simpler substance by chemical or physical
means.
• An element is made up of one kind of atom. If it has molecules,
the molecules are combinations of one kind of atom only.
Two Classes of Elements: Metals and Nonmetals
• Most elements are
metals that typically
are shiny, malleable
(mold like pasticine),
ductile (can be
drawn into wires)
and good
conductors of heat
and electricity.
• Some elements are
nonmetals which
typically are dull,
crumbly, poor
conductors of heat
and electricity, and
may be gases.
Compounds
• A compound is a homogeneous pure substance (fixed
properties) that is made up of molecules which have more than
one kind of atom.
• Compounds CAN be broken down into simpler pure substances
(elements)
Compounds can be broken down into simpler
elements.
• When orange mercuric oxide is heated, gaseous oxygen
and liquid mercury are formed.
Two Main Classes of Compounds: Ionic and Covalent
• Ionic compounds are made
up of positive and negative
ions. These compounds
are formed from metallic
atoms and nonmetallic
atoms when the metallic
atoms give one or more
electrons to the nonmetallic
atoms.
• Covalent compounds are
made up of neutral
molecules formed when
nonmetallic atoms share
electrons with other
nonmetallic atoms.
Particle Patterns in Substances
What would you classify foggy air as?
What would you classify paradichlorobenzene as?
• PDB breaks down into carbon, chlorine and hydrogen.
• Cooling curve of PDB shows a long flat line at 52.4
Celsius
The Law of Definite Proportions
• When elements combine to form a compound, they
combine in a definite proportion by weight.
When carbon combines with oxygen, two
compounds are possible. In one the weight ratio is
16:12 (1.33:1) and in the other, 32:12 (2.67:1)