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Purpose:
When a metal combines with a non-metal to form an ionic compound
they combine in discrete ratios that are determined by their valence
electrons, e.g. 2 Aluminum atoms will combine with 3 Oxygen atoms
to form Aluminum Oxide (Al2O3). Each Aluminum
atom has a charge of +3 (wants to donate 3 electrons)
and each Oxygen has a charge of -2 (wants to receive
2 electrons). To form a stable compound each donor and receiver
must be satisfied. Using visual manipulatives like Lego (or paper
cutouts) will help you to see why compounds combine in the ratios
they do. This information is vital to learning how to combine
and balance compounds in chemical reactions
(next chapter).
Setup/Procedure:
The following example illustrates: Potassium (K) and Arsenic
(As) combining to form Potassium Arsenide (K3As), Aluminum (Al)
and Oxygen (O) combining to form Aluminum Oxide (Al2O3), and how
both Potassium Arsenide (K3As) and Aluminum Oxide (Al2O3) chemically
react together (double replacement reaction) to form 2 new compounds
(next chapter).
First, the charge of each ion is determined by using the periodic
table (K = +1, As = -3, Al = +3, O = -2). Each ion is assigned
a uniquely colored game piece that matches this charge in size (
K(+1) = [ O ] , Al(+3) = [
O O O ] , etc). The metal piece are then locked to the
non-metal pieces until the layers of each are identical in length,
i.e. the charges are balanced.
| K(+1) |
+ |
As(-3) |
= |
K3As |
| [
O ] |
+ |
[
O O O ] |
= |
[O][O][O]
[ O O O ] |
| |
|
|
|
|
| Al(+3) |
+ |
O(-2) |
= |
Al2O3 |
| [
O O O ] |
+ |
[
O O ] |
= |
[
O O O ][ O O O ]
[ OO ][
OO ][ OO ] |
How these will be used in the next chapter in a double replacement
reaction!
| K3As |
+ |
Al2O3 |
= |
K2O |
+ |
AlAs |
[O][O][O]
[ O O O ]
[O][O][O]
[ O O O ] |
+ |
[
O O O ][ O O O ]
[ OO ][
OO ][ OO ] |
= |
[O][O]
[ OO ]
[O][O]
[ OO ]
[O][O]
[ OO ]
|
+ |
[
O O O ]
[ O O O ]
[ O O O ]
[ O O O ] |
| 2 K3As |
+ |
1 Al2Se3 |
= |
3 K2Se |
+ |
2 AlAs |
Problems:
Metal / Charge (+)
draw piece |
Non-Metal / - Charge (-)
draw piece |
Compound Formula
name
draw balanced pieces |
Al(+3)
[ O O O ] |
O(-2)
[
O O ] |
Al2O3
Aluminum Oxide
[ O O O ][ O O
O ]
[ OO ][
OO ][ OO ]
|
Li
|
C
|
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Be
|
N
|
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Al
|
O
|
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Sn
|
F
|
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Na
|
P
|
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Mg
|
Si
|
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In
|
As
|
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Pb
|
Ge
|
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Ga
|
Cl
|
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Ca
|
S
|
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Conclusion:
Finally, update your website with a short descriptive summary and all
10 compound formulas and names. The instructor will grade this lab
web entry according to this rubric.
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