Transcript 4 hon chem classifying matter b

Laws and theories
Law – a generalization that describes the
behavior of nature.
i.e. Newton’s Laws of Motion
Law of Definite Proportions
Theory – an explanation of observations
i.e. Darwin’s Theory of Evolution
Dalton’s Atomic Theory
Classes of matter
Matter
Pure substance
element
compound
mixture
homogeneous
heterogeneous
Solutions
Solutions are homogeneous mixtures.
A solute (the dissolved substance) is put in
a solvent (the dissolving substance).
The solvent is the substance there is more
of.
Examples
elements
Carbon
Iron
Gold
Mercury
compounds
water
carbon dioxide
table salt (NaCl)
aspirin
homo mix
air
salt water
white gold
brass
hetero mix
concrete
milk
wood
sand
General classes of elements
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Metals – have luster (shine)
are malleable (not brittle)
are ductile (can be drawn into wires)
conduct heat and electricity
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Nonmetals- poor conductors of heat and electricity
brittle
Metalloids- have characteristics of metals and
nonmetals
Brown, LeMay, Burstein “Chemistry: The Central Science
Chemical symbols
First letter is always capitalized.
 Second letter, if there is one, is never
capitalized.
 Co and CO are very different!
 Some elements use the Latin name
2O means 2 oxygen atoms
O2 means two oxygen atoms are chemically
bonded together.
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Law of Definite CompositionEvery compound has a definite
composition by weight.
- the % weight of each element
in a compound is always the
same.
Physical properties
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Can be determined without changing the
identity of the material
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Freezing point
Boiling point
Color
Odor
Hardness
Density
Solubility
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Extensive Properties
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Depend on how much (the extent) matter
there is
i.e. length, mass, volume
Intensive Properties
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Do NOT depend on how much matter there is
i.e. temperature, density (m/V)
Properties change at nanoscale
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Types of properties
 Optical (e.g. color, transparency)
 Electrical (e.g. conductivity)
 Physical (e.g. hardness, melting point,
diffusion rate)
 Chemical (e.g. reactivity, reaction rates)
Properties are usually measured by
looking at large (~1023) aggregations of
atoms or molecules
Chemical Properties
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Describe the behavior of a material in
reactions that change its identity
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Combustibility
Reactivity with other substances
Which chemical and physical properties should a roofer
consider when selecting material for a metal roof?
Physical Changes
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are those in which the identifying
properties of a substance are unchanged
Ex. : change of phase
breaking, cutting
dissolving
Chemical Changes
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are those in which different substances
are formed
Ex.: burning
rusting
decaying or spoiling
acid reacting with metal
Chemical Changes
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are those in which different substances
are formed
Ex.: burning
rusting
decaying or spoiling
acid reacting with metal
Ice changing to liquid water
Physical change
Water breaking down into
hydrogen and oxygen gases
Chemical change
Signs of a chemical change
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Heat gained or lost
Production of a gas
Formation of a precipitate
Color change
Methods of separating a mixture
Use the different properties of the
substances to separate them.
 Sand and iron filings Remove iron with magnet
 Sand and salt
Dissolve salt, evaporate water
filter
 Sand in water
 Water from salt water Distill the water
Settle and extract
 Oil in water (immiscible liquids) less dense liquid
Paper chromatography
 Mixture of pigments
chromatography
distillation
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Substance – a homogeneous material
consisting of one kind of matter
Compound – a substance that can be
decomposed into simpler substances only
by chemical means
Element – substances that cannot be
further broken down.
Organic substance contain carbon