TAKS 8th Grade Science Review Objective 3

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TAKS 8th Grade Science ReviewObjective 3

• Structures and Properties of Matter

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Remember all the information given to you on this
page!
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Information from the Periodic Table

• Groups columns (18) elements with similar
  physical and chemical properties
• Periods rows (7) energy levels of the
  outermost electrons (valence electrons)
• Valence Electrons farthest from the nucleus or
  most loosely held (key to how an atom reacts!)

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Note the locations of the metals, halogens and
noble gases.
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Elements found in which shaded area of this
periodic table undergo the fewest chemical
reactions? A Q B R C S D T
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Element Information
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Atomic Number
-
Number of Protons

C
-
Symbol
n

Starts w/ a Capital
n
n


-
-


n
n
12.011

Atomic Mass
n
Protons Neutrons
-

n
Name of Element
Carbon
-
How do you determine the number of Neutrons ?
n
Subtract the Atomic Number from the Atomic Mass
12 6 6
-



n
n
How do you determine the number of Electrons ?
-
In a stable atom, the number of protons equals
the number of electrons 6 6

-

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Parts of an Atom
Part Charge Location
Protons Positive Nucleus
Neutrons Neutral Nucleus
Electrons Negative Orbit

n
-
-
-
-
-
n


O
n
n
Valence Electrons farthest from the nucleus or
most loosely held (key to how an atom reacts!)
n
-

-
n



n
n
n


-
-
Dot Diagram consists of the symbol for an
element surrounded by the number of valence
electrons
-
H

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Atom vs Molecule
Molecule a combination of two or more atoms
bonded together
Atom the smallest particle of an element
-
-
-
-
-
n
-
-

-

n
n
n
n
-


-

n


n
n

n
-
n
n
n

-
n





n
n
n


-
-
-
-
-
-


What is this element?
Which molecule does this represent?
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TAKS Questions
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• A certain atom has a nucleus containing six
• protons and eight neutrons and has six
• electrons orbiting the nucleus. This atom is a
• form of the element
• A silicon
• B carbon
• C magnesium
• D calcium

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Ions

• Ions are atoms with either extra electrons or
  missing electrons.
• A normal atom is called a neutral atom, that is
  an atom with a number of electrons equal to the
  atomic number.
• You are a sodium (Na) atom. You have 11 , one
  too many to have your outer shell filled. You
  need to find another element who will take that
  away from you. Bring in chlorine (Cl). Chlorine
  (Cl) will take that electron away and leave you
  with 10 inside of two filled shells. You are a
  happy atom. Now you are also an ion, missing 1
  . You are a sodium ion (Na). You have one less
  electron than your atomic number. What about the
  chlorine atom? Is it an ion?

-
-
-
-

NaCl Sodium Chloride
-

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Isotopes
Let's say an atom is missing a neutron or has an
extra neutron. That type of atom is called an
isotope. An atom is still the same element if it
is missing an electron. The same goes for
isotopes. They are still the same element. They
are just a little different from every other atom
of the same element. Lets look at carbon
isotopes. There are a lot of carbon atoms in the
universe. The normal ones are carbon-12. Those
atoms have 6 neutrons. There are a few straggler
atoms that don't have 6. Those odd ones may have
7 or even 8 neutrons. Carbon-14 actually has 8
neutrons (2 extra). C-14 is considered an isotope
of the element carbon.
RETURNING TO NORMAL If we look at the C-14 atom
one more time we can see that C-14 does not last
forever. There is a point where it loses those
extra neutrons and becomes C-12. That loss of the
neutrons is called radioactive decay. That decay
happens regularly like a clock. For carbon, the
decay happens in a couple of thousand years. Some
elements take longer and others have a decay that
happens over a period of minutes.
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Practice with Molecules
Symbol Element Atomic Number Atomic Mass Protons Electrons Neutrons
 Na Sodium 20  40.8  20 20 20
      80    
      6 2    
H            
        6   
Co            
     120    47  
Au            
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Interpreting Chemical Formulas
CO2
3Fe2O3
2C6H12O6
C O
1 2
Fe O
2 3
x 3
C 6 x 2 12 H 12 x 2 24 O 6 x 2 12
6 9
x 3

• List your elements
• How many atoms of each element? The number behind
  the symbol. If there is no number behind the
  symbol, there is 1 atom of that element.
• Multiply by the number of molecules (coefficient
  - the number in front)

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Practice with Compounds
Chemical Formula Element 1 Element 2 Number of Atoms (Element 1) Number of Atoms (Element 2) Atomic Mass 1 Atomic Mass 2 Atomic Weight
 H2O  Hydrogen  Oxygen 2 1 1.008 x 2 16 x 1 18.016
CO2    
KCl    
Fe2O3          
(PO4)2          
AgBr          
HCl          
MgO          
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Law of Conservation of Mass

• Two lab students in IPC class mix calcium with
  zinc carbonate. According to the law of
  conservation of mass, what other product was
  produced and how much?
• A 0.088 kg of zinc
• B 0.088 kg of calcium
• C 0.104 kg of zinc
• D 0.104 kg of calcium

Zn
104 g
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Balancing Equations

• Mg O2 MgO

2
2
Mg O
1 1
x 2 2
Mg O
1 2
x 2 2
x 2 2
2
2
4
3
4

1. List your elements
2. How many atoms of each element?
3. Multiply by the number of molecules (coefficient)
4. Total. If they are even on both sides, the
   equation is balanced.
5. Balance the equation by adding molecules only!
   (Use multiplication)

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TAKS Questions

• K H2O ? KOH H2
• What is the coefficient for H2O when the
• above equation is balanced?
• A 1
• B 2
• C 3
• D 4

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Types of Chemical Reactions

• Have you heard of Hydrogen Peroxide?
• What are some of its uses?
• H2O2 ? H2O O2
• What happens to H2O2?
• What happens when something decomposes?

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Decomposition Reaction

• The breakdown of hydrogen peroxide is known as a
  decomposition reaction.
• Lets balance the chemical equation
• ___H2O2 ? ___H2O ___O2

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Single and Double Replacement Reactions
A
A
A
A
B
B
B
B
C
C
C
C
D
D

• Cl2 NaBr NaCl Br2
• Mg HCl MgCl2 H2

K2SO4 CaCl2 KCl CaSO4
Al(NO3)3 NaOH Al(OH)3 NaNO3
A
A
B
B
C
D
D
C
A
A
B
B
C
C
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Recognize this chemical reaction!

• Plants use carbon dioxide and water with sunlight
  to provide animals sugar, oxygen and energy.
• Help us translate this sentence into a chemical
  equation.

CO2 H2O sunlight ? C6H12O6 O2 ATP
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Respiration

• In the chemical reaction, Respiration, animals
  produce some CO2and H2O
• Can we leave the chemical reaction like this?
  What are we suppose to do?
• __C6H12O6 __O2 ? __CO2 __H2O

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Balancing Equations
CO2 H2O C6H12O6 O2 Mg HCl
MgCl2 H2

• Mg O2 MgO
• Cl2 NaBr NaCl Br2

K2SO4 CaCl2 KCl CaSO4
Al(NO3)3 NaOH Al(OH)3 NaNO3