With Dr. Wieser
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Chemistry can be defined as the study of
matter.
Matter is anything that has mass and
occupies space. So chemistry is the study of
pretty much everything.
We will focus on the structure of matter and
the changes that matter can undergo.
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A chemical is defined as any substance that
has a definite composition.
Look around the room-how many chemicals
can you observe?
There are many different branches of
Chemistry. See p4.
Also on PP4-5-different types of research are
discussed.
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We can define matter as anything that has
mass and occupies space. All matter is
composed of atoms. Elements and
compounds are made up of atoms.
An atom is the smallest unit of an element
that has the properties of that element. An
element is a pure substance and can not be
broken down into simpler substances.
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A compound is a pure substance that is made
of two or more elements that can be broken
down into simpler substances.
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Matter can exist in four states (three are
found on Earth)
Solid
Liquid
Gas
Plasma (found in the interior of the sun)
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Note that energy must be supplied to go from
one state or phase to another:
Solid →liquid→gas
Solids-have fixed volume and shape.
Liquids-have fixed volume but take on the
shape of their container.
Gases-have neither fixed volume or shape.
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In addition to phase changes matter can
undergo other physical changes:
Physical changes do not produce any new
substances:
What happens to an ice cube when heat is
supplied?
What about when sugar is dissolved in water?
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Chemical changes produce new substances.
In a chemical reaction one or more
substances, the reactants are converted to
one or more new substances, the products.
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A physical property is one that describes a
physical change. When considering phase
changes, the melting point of a substance is a
physical property. In the case of ice, this
temperature is______oC.
A chemical property describes the chemical
change. Paper undergoes a chemical change
when it burns, so the ability to react with
oxygen is a chemical property of paper.
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Compounds and elements are both pure
substances.
Compounds are a chemical combination of
two or more elements.
Mixtures are a physical combination of two or
more pure substances.
Mixtures that are uniform in composition are
called homogenous mixtures (sugar in water)
Mixtures that are not uniform are
heterogeneous mixtures (sand in water)
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Homework: always due at the beginning of
the next class period.
P 14 #’s 1-2-4
And p22 #’s 10-12
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I mentioned previously that elements are
composed of atoms. The periodic table lists
all the known chemical elements.
The columns are called groups or families –
there are 18 of them.
The rows are called periods. (see p 17).
There are three types of elements shown on
the table.
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Metals
Non-metals
Metaloids or semi-metals
Pages 18-20 give examples.
Homework for section 3
Page 20 #’s 1-4
END of Chapter 1 a test will follow.
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Observation
Hypothesis
Observation or experiment
Theory
Observation or experiment
Law
See page 31
15
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Scientists ask questions and make
observations.
A hypothesis is a possible explanation for an
observation. A hypothesis must be testableusually by performing an experiment and
analyzing the result.
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Experiments are conducted under controlled
conditions.
If the results of an experiment may support the
hypothesis- which will lead to more experiments or
not support it-then you need to look for a new
hypothesis or the result may lead you in a whole
new direction.
If over a relatively long period of time many
experiments support the hypothesis then the
hypothesis can become a theory.
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A theory is the best current explanation for a
series of observations. If new information
becomes available in the future then the
theory may be modified or even replaced.
This is all part of the scientific method!
In the course of performing experiments,
sometimes a cause and effect relationship is
observed.
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This relationship is a scientific law-scientific
laws do not explain observations but point
out connections between observations. For
example later in the year we will study the
Gas Laws-one says that when the
temperature of a gas goes up so does its
volume-the theory that explains this
observation is called the Kinetic Theory of
gases.
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One of the key parts of the scientific method
is the ability to make measurements.
If I told you a measurement was 59.7. What
would be your response?
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The metric system is the one used in science.
The units are called SI units-we will see that
not all the units we will use are SI units.
SI base units are listed on p 34.
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Some for you to try:
a. 1.34 g to kg
b. 15.2 cm to m
c. 2580. mg to kg
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Derived units: many measurements use more
complicated units derived from the base
units. For example volume (l x w x h)
requires a cubic unit, if the measurements
were in meters the unit would be m3.
The non-SI unit we commonly use for
volume is the liter which is equivalent to
a dm3 or 1000 cm3 (1000 mL)
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One important physical property of matter is
density .
Density = mass/volume
Every substance has its own unique density.
See p 17 for a list.
Since the density formula has 3 variables, 3
types of problems are possible.
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1. given mass and volume-find density
a substance has a mass of 23.2 grams and a
volume of 18.5 cm3. Find its density.
2. given density and volume, find mass (g)
D = m/V so m=D x V
The density of silver is 10.5 g/cm3. Find the
mass of a block of silver with a volume of
40.0cm3.
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3. Given the density and mass, find the
volume of a substance.
D= m/V so V= m/D
Find the volume of a piece of iron that has a
mass of 147grams. (from p 17 density of
iron = 7.86 g/cm3)
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Substances (pure)
- matter in which all samples have identical
composition and properties.
Elements
◦ substances that cannot be decomposed into
simpler substances via chemical reactions
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Elemental symbols
◦ found on periodic chart
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Compounds
◦ substances composed of two or more elements in a
definite ratio by mass
◦ can be decomposed into the constituent elements
 Water is a compound that can be decomposed into
simpler substances – hydrogen and oxygen
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The properties(chemical and physical) of
compounds are unique and are totally
different from the elements that make up the
compound.
Sodium chloride for example.
NaCl
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Mixtures
◦ composed of two or more substances
◦ homogeneous mixtures
◦ heterogeneous mixtures
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