chapter 2 matter and atoms 2.1 matter and the elements
TRANSCRIPT
CHAPTER 2
Matter and Atoms
2.1 Matter and the Elements
2 2.1 Matter and the Elements
What are things made of?
How many different kinds of substances can you identify?
3 2.1 Matter and the Elements
The “stuff” that we are made of is called matter.
Chemistry tells us how one kind of matter can be changed into a completely different kind of matter.
What are things made of?
4 2.1 Matter and the Elements
substance: a kind of matter that can’t be separated into other substances by physical means such as heating, cooling, filtering, drying, sorting, or dissolving.
Corn oil is a pure
substance
5 2.1 Matter and the Elements
mixture: matter that contains more than one substance.
Corn oil is a pure
substance
Oil and vinegar dressing is
a mixture of substances
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Is “pure orange juice” a pure substance?
“Pure orange juice”
• Water• Flavoring chemicals• Citric acid• Sugars• Fruit pulp• …
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Look at your desk – What is it made of?
wood, metal…
Can you think of a few physical properties?
is it heavy?
is it bendable?
does it feel cold?
can you scratch it?
…
8 2.1 Matter and the Elements
Examples: MassDensityColor
Physical properties can be measured or seen through direct observations.
Physical properties
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Physical changes include changes in shape, phase or temperature.
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11 2.1 Matter and the Elements
Chemical properties are observed when a substance changes into a different substance.
Iron RustChemical change
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Signs that a
chemical change has occurred
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Macroscopic and microscopic scales
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Each element is a unique type of atom.
All oxygen atoms are identical.
An oxygen atom is different from a silicon atom or a potassium atom.
element: a substance that cannot be separated into simpler substances by chemical means.
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1 grain of rice = 0.01 gram
1 hydrogen atom = 1.678 x 10–24 grams
= 0.000000000000000000000001678 grams
How small is an atom?
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How would you organize all those elements?
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The periodic table
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19 2.1 Matter and the Elements
The periodic table organizes elements according to how they
combine with other elements (based on their chemical properties).
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21 2.1 Matter and the Elements
Increasing atomic number
Incr
easi
ng
ato
mic
nu
mb
er
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HydrogenLightest elementAtomic number: 1
UraniumHeaviest naturally occurring elementAtomic number: 92
Increasing atomic number
Incr
easi
ng
ato
mic
nu
mb
er
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Elements that belong to the same group (column)
have similar chemical properties.
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Reminder
1 atomic mass unit (amu) = 1.66 x 10-24 g
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The atomic mass is the mass of:
1) a single atom in amu.
2) a mole of atoms in grams.
One single hydrogen atom weighs 1.01 amu.
One mole of hydrogen atoms weighs 1.01 g.
What does that mean?
26 2.1 Matter and the Elements
The atomic mass is the mass of:
1) a single atom in amu.
2) a mole of atoms in grams.
One single carbon atom weighs 12.0 amu.
One mole of carbon atoms weighs 12.0 g.
What does that mean?
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One mole contains 6.02 x 1023 atoms
Avogadro’s number
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How many moles are in 100 g of sulfur (S)?
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How many moles are in 100 g of sulfur (S)?
Asked: The number of moles
Given: The element is sulfur and there are 100 g
Relationships: One mole of sulfur has a mass of 32.065 g
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How many moles are in 100 g of sulfur (S)?
Asked: The number of moles
Given: The element is sulfur and there are 100 g
Relationships: One mole of sulfur has a mass of 32.065 g
Solve:
Answer: 100 g of sulfur contains 3.12 moles of sulfur atoms.
1100
32.0653.12
mole Sg S
g Smoles S
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How many grams of calcium (Ca) do you need to have 2.50 moles of calcium?
Asked: The number of grams
Given: The element is calcium and there are 2.50 moles
Relationships: One mole of calcium has a mass of 40.078 g
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How many grams of calcium (Ca) do you need to have 2.50 moles of calcium?
Asked: The number of grams
Given: The element is calcium and there are 2.50 moles
Relationships: One mole of calcium has a mass of 40.078 g
Solve:
Answer: 2.50 moles of calcium has a mass of 100. g.
40.0782.50
1100.2
g Camoles Ca
mole Cag Ca
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Physical properties can be seen
and measured
Chemical properties are observed
when one substance is changed into
another
Elements are
organized in
a periodic table This allows to convert grams to moles and vice versa.
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