1. Unit 2 How do we determine structure? Central goal:
DISCUSSION
Central goal:
To predict the molecular geometry of chemical substances.

2. Copper Carbonate (CuCO3)
Minerals
Most minerals do not contain metals in their native form, but combined as part of chemical compounds.
Copper Carbonate (CuCO3)
Copper (Cu)
The copper in this compound exists as a positive metallic ions (Cu2+) combined with “molecular” negative ions (carbonate- CO32-).
Show them a metal and a jar of a metal salt to show the difference and help prod the discussion.

3. Ionic Compounds
Many minerals are a mixture of these types of “ionic compounds” composed of positive ions (Na+, Cu2+) of a metal and negative ions of a non-metal (Cl-) or a molecular ion (NO3-).
NaCl
Na+ - cation
Cl- - anion
Sodium Chloride
You will have to introduce the basic ideas about ionic compounds. This is an opportunity to revisit and introduce
Some basic nomenclature for ionic compounds.
NO net charge
For these compounds, the chemical formula only indicates the ratio of + to – ions in the lattice (1:1).

4. Let’s Think
Let us consider the compound NaNO3 (Sodium Nitrate) composed of Na+ and NO3- ions.
Build the Lewis of the NO3- ion (Hint: Just add one more valence e- to the normal count);
Determine how many resonance structure does this molecular ion have?
Predict the e- pair geometry and molecular geometry of this ion;
Draw a particulate representation of NaNO3.
Have them work in groups. They have not worked with molecular ions in the lecture. However, this
Should not be very difficult if they understand the basic ideas of how to build Lewis Structures.

5. 5 + 3 x 6 + 1 = 24 valence e-  12 e- pairs
Lewis Structures
NO3-
What is the central atom? N
How many valence e-? How many pairs?
5 + 3 x = 24 valence e-  12 e- pairs
What is the backbone?
How do we distribute the e- pairs left?
We recommend to work with the whole group asking them to give the answers to each question.
How do we satisfy the octet rule for all atoms?
Form double bonds [ ] 1-

6. [ ] Molecular Structure 3 How many resonance structures? -
e- pair geometry and molecular geometry?
Both are Trigonal Planar
NO3-
Nitrate ion
Particulate representation?
It is important to constantly emphasize the network structure of ionic compounds, versus the molecular nature of molecular or covalent compounds.
Na+

7. Let’s Think
Let us consider the compound CuCO3 (Copper(II) Carbonate) composed of Cu2+ and CO32- ions.
Build the Lewis of the CO32- ion;
Determine how many resonance structure does this molecular ion have?
Predict the e- pair geometry and molecular geometry of this ion;
Draw a particulate representation of CuCO3.
This should be easy given that the structure of NO3- and CO32- are the same.
Keep insisting on their paying attention to the proportion of ions in the compound based on their charges.
Highlight the name of the compound and how we use roman numerals to indicate the charge of the ion
for most transition metals because they may be a variety of ions of the same metal.

8. 4 + 3 x 6 + 2 = 24 valence e-  12 e- pairs
Lewis Structures
CO32-
What is the central atom? C
How many valence e-? How many pairs?
4 + 3 x = 24 valence e-  12 e- pairs
What is the backbone?
How do we distribute the e- pairs left?
We recommend to work with the whole group asking them to give the answers to each question.
How do we satisfy the octet rule for all atoms?
Form double bonds [ ] 2-

9. [ ] Molecular Structure 3 How many resonance structures?2-
e- pair geometry and molecular geometry?
Both are Trigonal Planar
CO32-
Carbonate ion
Particulate representation?
Cu2+

10. Let’s Think
Let us consider the compound Na2C2O4 (Sodium Oxalate) composed of Na+ and C2O42- ions.
Build the Lewis of the C2O42- ion;
Determine how many resonance structure does this molecular ion have?
Predict the e- pair geometry and molecular geometry of this ion around each carbon atom;
What is the value of the largest bond angle in this molecular ion?.
Keep insisting on their paying attention to the proportion of ions in the compound based on their charges.

11. 2 x 4 + 4 x 6 + 2 = 34 valence e-  17 e- pairs
Lewis Structures
C2O42-
What is the central atom? C
How many valence e-? How many pairs?
2 x x = 34 valence e-  17 e- pairs
What is the backbone?
How do we distribute the e- pairs left?
We recommend to work with the whole group asking them to give the answers to each question.
How do we satisfy the octet rule for all atoms?
Form double bonds

12. Molecular Structure 4 ~ 120o How many resonance structures?
e- pair geometry and molecular geometry around C?
Both are Trigonal Planar
It is important to constantly emphasize the network structure of ionic compounds, versus the molecular nature of molecular or covalent compounds.
Largest bond angle?
~ 120o

13. Consider CaCO3  6H2O (Calcium carbonate hexahydrate)
Let’s Think
Some ionic compounds exist as “hydrates” (water molecules are part of their structure).
Consider CaCO3  6H2O (Calcium carbonate hexahydrate)
Analyze the structure of this compound and justify the arrangement/orientation of its different components.
Have them analyze the image carefully. The idea is that they notice how the negative parts of the molecules (H2O and NO3-) are closer to the positive charge. This is a way for them to visualize how these more complex ionic compounds are modeled. Emphasize the network structure.

14. Let’s Think Consider this ionic compound: Fe(NO3)3 9H2O
What are the main components of this compound? Indicate their electrical charges.
What is the chemical name of this compound?
How many gram of this compound would you need to prepare 100. mL of a M solution?
Fe3+ NO3- H2O
Iron (III) nitrate nonahydrate
This is an opportunity to see if they can apply some of the simple ideas already discussed.
M(Fe(NO3)3 9H2O ) = g/mol
We need moles = 40.4 g in 1 L,
or g in 100 mL.