2. Pure Substances
• Pure Substance that cannot be broken
down into any other substances by
chemical or physical means
Gold - element Manganese Dioxide - compound
3. Pure Substance
• Element
– composed of identical atoms
– EX: copper wire, aluminum foil
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4. Pure Substances
• Compound
– composed of 2 or more elements
in a fixed ratio
– properties differ from those of
individual elements
– Chemical bonds hold the
elements together
– EX: table salt (NaCl)
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5. Pure Substances
Law of Definite Composition
Law of Definite Composition
– A given compound always contains the same,
fixed ratio of elements.
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Two different compounds,
each has a definite composition
6. Molecules
• Groups of two or more atoms bound by
chemical bonds
• Can be two of the same element
11. Elements
only one kind
of atom; atoms
are bonded it
the element
is diatomic or
polyatomic
Compounds
two or
more kinds
of atoms
that are
bonded
substance
with
definite
makeup
and
properties
Mixtures
two or more
substances
that are
physically
mixed
two or
more
kinds of
and
Both elements and compounds have a definite makeup and definite properties.
Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page (Figure 2.4.1)
12. Mixtures
Variable combination of two or more
pure substances. Each keep individual
properties
Homogeneous- Evenly Mixed
cannot see different parts.
(Same)
Heterogeneous – Can
see different parts
(different)
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16. Mixtures
Suspension
– heterogeneous
– large particles
– Tyndall effect
– particles settle
– EX:
• fresh-squeezed
lemonade
• Sand in water
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17. Mixtures
Examples:
– mayonnaise
– muddy water
– fog
– saltwater
– Italian salad
dressing
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colloid
suspension
colloid
solution
suspension
18. Elements, Compounds, and Mixtures
(a)
an element
(hydrogen)
(b)
a compound
(water)
(c)
a mixture
(hydrogen
and oxygen)
(d)
a mixture
(hydrogen
and oxygen)
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd
Edition, 1990, page 68
hydrogen
atoms hydrogen
atoms
oxygen atoms
19. MATTER
Can it be physically
separated?
Homogeneous
Mixture
(solution)
Heterogeneous
Mixture Compound Element
MIXTURE PURE SUBSTANCE
yes no
Can it be chemically
decomposed?
no
yes
Is the composition
uniform?
no
yes
Colloids Suspensions
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20. Classification of Matter
MATTER
(gas. Liquid,
solid, plasma)
PURE
SUBSTANCES MIXTURES
HETEROGENEOUS
MIXTURE
HOMOGENEOUS
MIXTURES
ELEMENTS
COMPOUNDS
Separated by
physical means into
Separated by
chemical
means into
Kotz & Treichel, Chemistry & Chemical Reactivity, 3rd
Edition , 1996, page 31
21. Matter
Substance
Definite composition
(homogeneous)
Element
(Examples: iron, sulfur,
carbon, hydrogen,
oxygen, silver)
Mixture of
Substances
Variable composition
Compound
(Examples: water.
iron (II) sulfide, methane,
Aluminum silicate)
Homogeneous mixture
Uniform throughout,
also called a solution
(Examples: air, tap water,
gold alloy)
Heterogeneous mixture
Nonuniform
distinct phases
(Examples: soup,
concrete, granite)
Chemically
separable
Physically
separable
Classification of Matter
22. Mixture vs. Compound
Mixture
Fixed
Composition
Bonds
between
components
Can ONLY be
separated by
chemical means
Variable
Composition
No bonds
between
components
Can be
separated by
physical means
Alike Different
Contain
two or more
elements
Can be
separated
into
elements
Involve
substances
Compound
Different
Topic Topic
23. Compounds vs. Mixtures
• Compounds have properties that are
uniquely different from the elements from
which they are made.
– A formula can always be written for a compound
– e.g. NaCl Na + Cl2
• Mixtures retain their individual properties.
– e.g. Salt water is salty and wet
24. Top Ten Elements
in the Universe
Percent
Element (by atoms)
1. Hydrogen 73.9
2. Helium 24.0
3. Oxygen 1.1
4. Carbon
0.46
5. Neon 0.13
6. Iron 0.11
7. Nitrogen
0.097
8. Silicon 0.065
A typical spiral galaxy
(Milky Way is a spiral galaxy)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 26
25. The Composition of Air
Air
Nitrogen
Oxygen
Helium
Water
vapor
Neon
Carbon
dioxide
Argon
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 34
26. Chart Examining Some Components of Air
Nitrogen consists of molecules consisting of
two atoms of nitrogen:
Oxygen consists of molecules consisting of
two atoms of oxygen:
Water consists of molecules consisting of two
hydrogen atoms and one oxygen atom:
Argon consists of individual argon atoms:
Carbon dioxide consists of molecules consisting
of two oxygen atoms and one carbon atom:
Neon consists of individual neon atoms:
Helium consists of individual helium atoms:
N2
O2
H2O
Ar
CO2
Ne
He
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 35
#19:“Elements, Compounds, and Mixtures”
Description: This slide shows the molecular composition of an element, a compound, and two mixtures.
Basic Concepts
All samples of a substance have the same molecular composition and intensive properties and are homogeneous.
Elements and compounds are substances; mixtures are not.
The elements making up a compound combine in fixed ratios.
Mixtures can be separated by physical methods.
Mixtures that have a uniform composition throughout are homogeneous; those that have parts with different compositions are heterogeneous.
Teaching Suggestions
Use this transparency to help students visualize the molecular composition of elements, compounds, and mixtures and to review the definitions of these terms. Make sure students understand the difference between the terms matter and substance. Remind students that elements and compounds are always homogeneous, while mixtures can be either homogeneous or heterogeneous.
Questions:
Which of the bottles pictured above contain(s) matter? Which contain(s) a single substance? Explain your answers.
How many elements are present in each molecule of water shown in bottle (b)? What is the relative number of atoms of each element in a water molecule?
As you know, ice is frozen water. In other words, ice and water are the same substance, in different phases. What would you expect the ratio of hydrogen atoms to oxygen atoms to be in a molecule of ice? Explain your reasoning.
Bottle (c) and bottle (d) both contain mixtures. How are these mixtures similar? How are they different?
Suppose you find an unlabeled bottle containing a clear liquid. Can you tell by looking at it whether the material is a compound or a mixture? Explain your answer.
How can you prove that a sample of sea water is a mixture?
Classify the following items as elements, compounds or mixtures; rice pudding, copper, carbon dioxide, air, milk, magnesium chloride, granite, mercury, and maple syrup.
A chocolate-chip cookie with more chips in one part of the cookie than another can be used to demonstrate a heterogeneous mixture. Name two other materials that can be classified as heterogeneous mixtures. Explain your reasoning.
#22:Basis for separation: different components, different properties.
Strategy: devise a process that discriminates between components with different properties.
high density / low density reactive / inert volatile / nonvolatile
soluble / insoluble polar / nonpolar magnetic . nonmagnetic
#23:Compounds have different properties than the elements they are made from. In a mixture, the mixture retains the properties of the materials it is made from.
A chemical formula can always be written for a compound.
