PowerPoint Answers - Lewis Dot Diagrams and Ionic

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Ionic Compounds
Recall Ions:
-“+” on the left (metals) because they lose
electrons (become less negative)
- “-” on the right (non-metals) because they gain
electrons (become more negative)
-What is the total charge if you have X+1 and Y-1
-______________________________________
Ionic Compounds
• Metal and a non-metal combine to form "Ionic
Compounds".
• The metal atoms loses electrons to form
positive ions.
• The non-metal gains the electrons to form
negative ions.
• The two ions join together
• ______________________________________
• ______________________________________
Ionic Compounds
• Ionic compounds are formed
when a metal gives one or more
of its electrons to a non metal.
Ca
• When all of the electrons are
gone, the metal’s inner orbit of
electrons is full. So, the metal is
stable.
• ______
• ______
Ca+2
Ionic Compounds
• The non-metal receives one
or more electrons to fill its
outer shell and become
stable.
• If we draw the Lewis
Structure for a non metal
we include the full valence
orbit, brackets and a charge
• Having gained two
electrons, the Oxygen is
now negative.
• ____
O
-2
O
Ionic Compounds
• Putting the compound
together, we can see that
the overall molecule has a
neutral charge.
• This particular example is
simple because the
Calcium and Oxygen want
to exchange the same
number of electrons.
• What would happen if they
wanted to exchange
different numbers of
electrons?
-2
Ca+2
O
+2 – 2 = 0
Try it!
Using Lewis Structures:
Ionic bonding between Lithium and Oxygen
1. First draw the Lewis
structures of the atoms on
their own.
2. Now use an arrow to
show the electron
transferring from the
Lithium atom to the
Oxygen atom
3. You can see that the
Oxygen atom still does
not have a complete outer
shell. Clearly another
Lithium atom is required
to complete the
compound.
Li
O
Li
Lithium Oxide continued
• ______________________
Li+
-2
• ______________________
• The final Lewis structure is
illustrated here.
• ______________________
Li+
O
Illustrate the bonding between Aluminum and Oxygen. (Note the ratio
here is a little harder to find.)
• Draw the Lewis Structures of the
individual atoms.
• Use arrows to show the transfer of
electrons.
• Aluminum has one electron left,
we need another oxygen atom.
• The oxygen atom now needs more
electrons so we need another
aluminum atom.
• The extra electrons on the
Aluminum mean we need another
Oxygen.
• Since, we have been able to make
both atoms stable, we have hit the
correct ratio.
Al
O
Al
O
O
Aluminum Oxide Continued
Having _______3 electrons, the
aluminum has a charge of __.
Having ________2 electrons, the
oxygen has a charge of ___.
Now draw the final Lewis
Structure.
This structure is designed to
illustrate the transfer of
electrons while bonding.
-2
-2
O
O
Al+3
Al+3
-2
O
Naming Ionic Compounds
Naming these compounds is straight forward.
1. ______________________
2. ______________________
Examples – Sodium Chloride, Calcium Oxide
Writing the formulas for
Ionic Compounds
The trick to finding the ratio of atoms in the molecule.
The easiest way is to find the number of BONDS the ion will make is to
again refer to your period table
Writing the formulas for
Ionic Compounds
1.
2.
Number the groups 1-3 going from left to right (skip the Tansition Metals)
Number the groups 1-3 going from right to left (skip the Nobel Gases)
1
2
3
3 2 1
Writing the formulas for
Ionic Compounds
•
•
______________________
______________________
+1
+2
+3
-3 -2
-1
Then …
Write out the atoms with their stable charge
Al+3O-2
Cross over the numbers to the opposite atom (CrissCross Rule!)
Al2O3
____
Criss-Cross Rule
Example: Aluminum Chloride
Step 1:
Aluminum
Chloride
write out name with space
Step 2:
Al+3
Cl-1
Al
Cl 3
write symbols & valence number
Step 3:
1
criss-cross valence number as subscripts
Step 4:
combine as formula unit
(“1” is never shown)
- Reduce if possible
AlCl
3
Criss-Cross Rule
Example: Magnesium Oxide
Step 1:
Magnesium
Oxide
Step 2:
Mg+2
O-2
Step 3:
Mg
O2
2
Step 4:
Mg2O2
Step 5:
MgO
Multivalent Compounds
• _____
• When atoms get larger, their
atomic structure can become more
complex.
• This means that some atoms can
have different numbers of valence
electrons in different situations.
• For example if we look at the
Lewis structure of Copper. It
can have one valence electron
or two valence electrons.
Cu
Cu
• Clearly, this atom can form
more than one type of
molecule.
-2
-2
Cu+1
O
Cu+1
Cu+2
O
Multivalent Compounds
• In terms of naming these compounds,
we need a method of distinguishing,
CuO
and Cu2O
e.g. Write the name for the
following compounds,
CuF
Copper (I) Fluoride
• ______________________
PbI2
______________________
• ______________________
CaF2
______________________
• The roman numeral is only included if
the metal is one of the atoms that can
exhibit more than one charge.
• This information will be provided!
How do we know which roman
numeral is being used?
CuF
- ______________________
- ______________________
Cu 1 F1
Cu +1 F-1
Copper (I) Flouride
PbI2
Lead (II) Iodide
Pb 1 I2
Pb +2 I-1
• ________
• ________
• Be careful when you are asked to determine the roman
numeral given the formula (e.g. CuS)
•This would lead you to answer: Copper (I) Sulfide
•However we ALWAYS NEED TO CHECK THAT THE
CHARGE ON THE ANION IS CORRECT
•In this case it would be -1 however, if we look at the
periodic table we know that S is -2
•Therefore we need to multiply both charges by 2
• Copper (II) Sulfide
• __________
Ionic Compounds
• Many ionic compounds are soluble in water.
• When they dissolve, they separate into ions.
• Water molecules surround each ion preventing it them from
rejoining
Ionic Compounds Properties
• ______________________
• Many are also electrolytes which means they
conduct electricity when dissolved in water
• Pure water is a poor conductor of electricity,
dissolved ions improve this property
considerably

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