STAAR Reporting Category 1
Matter & Energy
Middle School Science
Science STAAR Need to Know
STAAR Need to Know
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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 STAAR 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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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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Evidence of a Chemical Reaction





a change in odor,
a change in color,
a solid precipitate is formed,
a gas is formed,
there is either absorption or release of heat
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Chemical Equations
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