STAAR
Structure and Properties of
Matter
Middle School Science
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Atomic Theory

Atoms are building blocks of elements

Atoms in each unique element are the same.
(Ex: Every oxygen element has the same # of protons)

Atoms are different from atoms of other elements
(Ex: Hydrogen has a different # of protons than oxygen)

Two or more different atoms bond in simple ratios to
form compounds
(Ex: Hydrogen & oxygen can
chemically combine to form water- H2O )
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Atoms and Elements
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Atomic Particle Charges
Protons Positive +
Neutrons Neutral =
Electrons Negative TAKS Need to Know
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Location of Subatomic Particles
10-13 cm
electrons
protons
nucleus
neutrons
10-8 cm
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Location of Atomic Particles
Inside the Nucleus
Outside the Nucleus- in
electron cloud
Protons with a Positive
charge
AND
Neutrons with a Neutral
charge –that means they
do not have a charge
Electrons with a
Negative charge
Did you know electrons
are very, very small and
move very, very fast???
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Periodic Squares
11
Na
22.99
The periodic square for an element
can tell you lots of information about that atom.
Atomic number = # of protons
Atomic number = # of electrons
That means in a neutral (uncharged) atom the # of
protons and electrons are always the SAME!!!!
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Atomic Mass on the Periodic Table
Atomic Number
or Protons
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Symbol
Atomic Mass or
Protons + neutrons
Na
22.99
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Atomic number
Atomic number =
# of Protons
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Mass Number
The number
of
protons and neutrons
in an atom
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Number of Electrons




A balanced atom is neutral
The net overall charge is zero
Number of protons = Number of electrons
Atomic number = Number of electrons
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Elements with similar properties are placed in the same
group in the periodic table.
The stair-step line separates the elements into metals
and nonmetals.
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Metals & Nonmetals
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Element
Chlorine-35
Iron-56
Magnesium-24
Lead-208
Nitrogen-14
Protons Neutrons Electrons
17
26
12
82
7
18
30
17
26
2 elements
with similar
properties
F and Br
Ru and Os
12
12
Ca and Sr
126
82
Sn and Ge
7
7
P and As19
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Specific Heat
Measure of how much
heat matter can absorb.
It is a measure of how
much heat energy it takes
to make 1 gram of a
substance rise 1o C in
temperature.
Heat is measured in
calories.
A calorie is the amount of
heat needed to make 1 g
of water rise 1o C in
temperature.
The higher a substance’s specific heat, the harder it is to increase its
temperature (as with the cloth car seat). The opposite is also true: a
substance with lower specific heat increases in temperature very easily
(as with the metal car door). TAKS Need to Know
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If you want to keep the temperature of
something from changing very much…build it
out of a material that has a high specific heat.
Most metals have low specific
heats, while nonmetal
compounds & mixtures such
as water, wood, soil, & air
have relatively high specific
heats.
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How the specific heat of water
affects the Earth
Oceans cover about 2/3 of Earth’s
surface. Water’s characteristic of
retaining heat is important to our climate.
It means that our climate stays much
more stable than it would if there were
less water on Earth.
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Molecules & Compounds
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Mixtures
Combination of two or more pure substances.
Substances are mixed together but have not
reacted to form any new molecules.
Example- Sugar (a compound) dissolves in water (a
compound) to form a mixture. The molecules of sugar
and water do not change chemically. They just
become mixed together.
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Properties of matter
Physical properties – can be observed
without changing the substance into a
different substance.
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Chemical Properties
Characteristics of a substance that are observed when it
reacts (changes) to produce one or more different
substances.
Example- Water can be changed into hydrogen gas and
oxygen gas using an electric current. When water
molecules change chemically into hydrogen gas and
oxygen gas, we say that a chemical change has occurred.
Hydrogen gas and oxygen gas each have a different set of
properties.
Substances change into different substances through
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chemical reactions.
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Chemical Reactions
Substances change into other
substances in chemical reactions.
The atoms in the original
substance are rearranged. The
bonds in the original substance
may be broken and new bonds may
be formed between different
atoms. This produces one or more
new substances that may be
either pure elements or
compounds.
The products of a chemical
reaction always have difference
chemical and physical properties
than the original substance(s).
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Chemical Equations
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