CHEMISTRYName ______

LAB – MOLECULAR MODELS

Most of our learning is in two dimensions. We often draw representations of molecules on flat paper. Although such models help us to understand the structure of molecules, flat models do not give us the three-dimensional view necessary for an accurate mental picture of most molecules.

In covalent molecules, single, double, and triple bonds form between atoms. Dot structures show a double bond as two pairs of shared electrons anda triple bond as three pairs. Kekule structural formulas use two parallel lines for a double bond and three parallel lines for a triple bond. In some cases, the atoms are arranged in straight chains. At other times, the chains are branched out. Still others take the form or a ring (circular shape) of atoms.

Model Building with Covalent Compounds.

1. Obtain a molecular model kit and look at the contents. Identify the atoms that will be represented as follows. List the color used for each element. Knowing what element looks like makes it easier to use the model kit.

ATOM / NUMBER OF BONDING SITES / COLOR
Hydrogen / 1
Oxygen, Sulfur / 2
Carbon / 4
Group 7 elements / 1
Nitrogen / 3

2.Draw a Lewis dot structure for each of the following molecules, and then build a model for each one. There is only on structural formula for each. When you are satisfied you have the correct structure, sketch it on the report sheet. Try to represent in your sketch the three-dimensional nature of these models.

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a. water H2O

b. methane CH4

c. methanol CH3OH

d. carbon tetrachloride CCl4

e. ammonia NH3

f. hydrogen chloride HCl

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g. carbon dioxideCO2

h. nitrogen gasN2

i. hydrogen cyanide HCN

dj. butene C4H8

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Report Sheet

MOLECULE / LEWIS DOT STRUCTURE / 3-D DIAGRAM
Water
Methane
Methanol
Carbon Tetrachloride
Ammonia
Hydrogen Chloride
Butanol
(4 isomers)
Dichlorethane
(2 isomers)
MOLECULE / LEWIS DOT STRUCTURE / 3-D DIAGRAM
Carbon Dioxide
Nitrogen
Hydrogen Cyanide
Butene
Butyne
Benzene

Questions:

1.A model of the molecule silicon tetrachloride, SiCl4 , might look similar to the model you constructed for methane, CH4 , but the substances are very different. What are some of the limitations of models for representing molecules.

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2.Cyclobutane has the same formula as butene,

but the name indicates a structure where the

carbon atoms are connected in a ring.

Sketch this compound in the space to the right.

3.Why is model building useful for studying chemical bonding ?

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4.Why are computer models of molecules useful ?

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Name: ______Molecular Models Lab

Purpose: To identify the shape of molecules and their polarity.

Pre-Lab:

1.What is the difference between and atom and a molecule?

2.How many electrons are shared in a single bond? A double bond? A triple bond?

3.Based on valence electrons, how many times can carbon bond? Oxygen? Nitrogen? Hydrogen?

Procedure:

1.Obtain a molecular models building set. Identify the different types of atoms based on the number of holes they have. Complete the chart below; indicating which colors can be used for different elements.

2.Fill in the second chart, which includes places to record Lewis dot structures of the molecules listed below, as well as their shape, a diagram of the model you will construct, and their molecular polarity. You should use the springs when constructing multiple covalent bonds.

Color / Atom / Color / Atom
Green (1 hole) / Red (2 holes)
Orange (1 hole) / Blue (4 holes)
Yellow (1 hole) / Black (4 holes)
Purple (1 hole)
Molecule / Lewis Diagram / Drawing
(In color) / Shape
(Linear, Bent, Pyramidal, Tetrahedral?) / Polarity
(P or NP?)
Hydrogen
(H2)
Water
(H2O)
Methane (CH4)
Chlorine
(Cl2)
Ammonia (NH3)
Hydrofluoric Acid (HF)
Ethylene (C2H2)
Nitrogen
(N2)
Carbon Dioxide
(CO2)
Oxygen
(O2)
Hydrogen Sulfide
(H2S)

Questions:

  1. How many unshared pairs are present in a molecule of O2 and H2?
  1. How many shared pairs are present in a molecule of C2H2?
  1. What happened to the shape of the molecule when double bonds (springs) were used?
  1. Which molecules were non-polar because all the bonds were non polar?
  1. Which molecules had polar covalent bonds but were non-polar due to the symmetry of the molecule?
  1. Which two shapes appeared to always produce polar molecules?

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Pre-Lab #2: Molecular Models Name ______

1. What do the balls and sticks in the model kit represent?

2. According to today’s lab, what is a valence shell?

3. What do the number of holes in each ball in the model kit represent?

1. Why do Hydrogen atoms form only single bonds with other atoms and not double or triple bonds like Carbon atoms?

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