Unit 2 How do we determine structure? Central goal:

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Unit 2How do we determine

structure?

DISCUSSION

Central goal: To predict the molecular

geometry of chemical substances.

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Most minerals do not contain metals in their native form, but combined as part of chemical compounds.

Copper (Cu)

Minerals

Copper Carbonate (CuCO3)

The copper in this compound exists as a positive metallic ions (Cu2+) combined with “molecular”

negative ions (carbonate- CO32-).

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Ionic CompoundsMany 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

For these compounds, the chemical formula only indicates the ratio of + to – ions in the lattice (1:1).

Na+ - cation

Cl- - anion

NO net chargeSodium Chloride

http://en.wikipedia.org/wiki/Image:Halite%28Salt%29USGOV.jpg

http://en.wikipedia.org/wiki/Image:Sodium-chloride-3D-ionic.png

http://en.wikipedia.org/wiki/Image:Sodium-chloride-3D-ionic.png

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Let’s Think

Let us consider the compound NaNO3 (Sodium Nitrate) composed of Na+ and NO3

- ions.

a) Build the Lewis of the NO3- ion (Hint: Just add

one more valence e- to the normal count);

b) Determine how many resonance structure does this molecular ion have?

c) Predict the e- pair geometry and molecular geometry of this ion;

d) Draw a particulate representation of NaNO3.

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Lewis StructuresNO3

-

1. What is the central atom?

2. How many valence e-? How many pairs?

5 + 3 x 6 + 1 = 24 valence e- 12 e- pairs

3. What is the backbone?

4. How do we distribute the e- pairs left?

5. How do we satisfy the octet rule for all atoms?

N

Form double bonds [ ]1-

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XXIMolecular Structure

How many resonance structures?

e- pair geometry and molecular geometry?

Both are Trigonal Planar

NO3-

Nitrate ion

Particulate representation?

Na+

3 [ ]- [ ]- [ ]-

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Let’s Think

Let us consider the compound CuCO3 (Copper(II) Carbonate) composed of Cu2+ and CO3

2- ions.

a) Build the Lewis of the CO32- ion;


c) Predict the e- pair geometry and molecular geometry of this ion;

d) Draw a particulate representation of CuCO3.

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Lewis StructuresCO3

2-



4 + 3 x 6 + 2 = 24 valence e- 12 e- pairs




C

Form double bonds [ ]2-

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e- pair geometry and molecular geometry?

Particulate representation?

Cu2+


CO32-

Carbonate ion

3 [ ]2- [ ]2-[ ]2-

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Let’s Think

Let us consider the compound Na2C2O4 (Sodium Oxalate) composed of Na+ and C2O4

2- ions.

a) Build the Lewis of the C2O42- ion;


c) Predict the e- pair geometry and molecular geometry of this ion around each carbon atom;

d) What is the value of the largest bond angle in this molecular ion?.

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Lewis StructuresC2O4

2-



2 x 4 + 4 x 6 + 2 = 34 valence e- 17 e- pairs




C

Form double bonds

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e- pair geometry and molecular geometry around C?

Largest bond angle?

4

~ 120o


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Let’s ThinkSome 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.

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Let’s ThinkConsider this ionic compound: Fe(NO3)3 9H2O

a) What are the main components of this compound? Indicate their electrical charges.

b) What is the chemical name of this compound?

c) How many gram of this compound would you need to prepare 100. mL of a 0.100 M solution?

Fe3+

NO3-

H2O

Iron (III) nitrate nonahydrate

M(Fe(NO3)3 9H2O ) = 403.999 g/mol

We need 0.100 moles = 40.4 g in 1 L,

or 4.04 g in 100 mL.

Unit 2 How do we determine structure? Central goal:

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