Building Molecular Models of Simple Covalent Molecules

Day Three

Before asking your teacher questions about how to do the lab, please read carefully, twice, the entire "Day Three" document.

Special Note: I will deduct 10% off your grade for playing with the model sets; as in "Look Mr. ChemTeam, at this weird structure I made" or if I see you making a structure not in the assignment. On the second occurrence, I will zero your grade.


Objective

1) Using a model building kit, construct models of a variety of simple covalent molecules.
2) Draw Lewis structures and/or structural formulas of selected models.
3) Draw all the isomers of selected formulas.

Brief Overview

In 1874, J. H. van 't Hoff (1901 Nobel Prize in Chemistry) was the first to suggest that molecules have a three-dimensional structure. He used this idea to explain several previously puzzling facts about chemical compounds.

In this lab, we will use a kit to model the 3D structure of a number of molecules, including several that van 't Hoff focused on. After building the molecular models, you will draw them on paper in a manner intended to represent the 3D appearence. You will also draw Lewis structures for some of the molecules as well as isomeric structures for those formulas that have them.

Safety

The parts of the kits are not toys. Use them only as instructed and only for the purposes of the lab.

Equipment List

One molecular model kit

Procedure

Part I. Preliminary Steps
1) If necessary, refer to Day One for instructions. If not, proceed directly to Part II.
Part II. Experimental Steps

2) Following the list below, continue to build models. There are not enough atoms to build all the molecules discussed below, so build some, then break them down, then build more.

a) Alcohols (5 structural, 4 Lewis) are compounds which have one (or more) -OH group(s) attached to a carbon. Some of the alcohols below have isomers in which there is no -OH group. These "non-OH" structures are not alcohols, so do not include them here. They will appear elsewhere. Build the following models:
1. methanol, CH3OH (also called methyl alcohol) A picture of methanol
2. ethanol, C2H5OH (also called ethyl alcohol) A picture of ethanol
3. propanol, C3H7OH (also called propyl alcohol) A picture of propanol
4. butanol, C4H9OH (also called butyl alcohol) A picture of butanol

Note that there is an isomer for C3H7OH, which differs only in the placement of the -OH group. They are structural isomers of one another. In your data table, draw both. Here is a picture of both models. The straight chain alcohol is named n-propanol, the one where the -OH group branches off is named 2-propanol (the older name is isopropyl alcohol, also called rubbing alcohol).

Note that there is only one structure shown for butanol; its name is n-butanol. There are three other isomers (with the formula C4H9OH) in which the -OH group is preserved. This will be followed up in the discussion section.

b) Ethers (4 structural, 2 Lewis) are substances which contain an oxygen which is itself bonded to two other carbons. Any substance which contains a C-O-C arrangement in it is considered an ether. Build the following models:

5. dimethyl ether, CH3OCH3 A picture of dimethyl ether
6. methyl ethyl ether, CH3OC2H5 A picture of methyl ethyl ether
7. diethyl ether, C2H5OC2H5 A picture of diethyl ether (the top structure)
8. Can you name the bottom structure in the picture linked just above? Hint: it starts with "methyl" and ends with "ether" and there is one more word in between. Draw its structure in the data table.

c) Aldehydes (2 structural, 2 Lewis) are substances that have a double bonded oxygen connected to a TERMINAL carbon (the end carbon in a chain). There also MUST be a hydrogen connected to the terminal carbon. Build the following models:

9. methanal, CH2O (also called formaldehyde) A picture of methanal
10. ethanal, CH3CHO (also called acetaldehyde) A picture of ethanal

d) Ketones (1 structural, 1 Lewis) are substances that have an oxygen double bonded to a carbon and the carbon is NOT a terminal carbon. Build the following model:

11. acetone, CH3COCH3 A picture of acetone

e) Acids (2 structural, 2 Lewis) are substances that have two atoms attached to a terminal carbon: a double bonded oxygen AND an -OH group. Both are attached to the SAME carbon. Build the following models:

12. methanoic acid (also known as formic acid), HCOOH A picture of methanoic acid
13. ethanoic acid (also known as acetic acid), CH3COOH A picture of ethanoic acid
Part III. Clean-up Steps
3) Unconnect all bonds from the atom models and replace in the box. Inspect around your table top and on the floor for lost atoms or bonds.

Data Table

Do a data table in the style of the Day One instructions. There are 14 structural formulas and 11 Lewis structures to be drawn.

Discussion

Isomers for C4H9OH

There are 4 isomers which have the formula C4H9OH. Note that it is important to preserve the -OH group. I want you to draw all 4 structures. This means I want you to draw the n-butanol structre a second time, then figure out the other three. Keep in mind that structural isomers have different connectivities and that this means you must remove a piece of the structure and put it somewhere else. Also, keep in mind that if, by bending and twisting only, you can convert your "new" structure into the "old" structure, then they are the same substance and are NOT isomers.

Hint: move the -OH group to get create possible isomers as well as moving a carbon. If you get more than 4 (all with the -OH group preserved), then you have duplicate structures.

Isomers for C5H11OH

There are 8 isomers which have the formula C5H11OH and which preserve the -OH group. Information about the isomers may be found here.

By the way, there are six additional isomers for C5H12O which do not preserve the -OH. These six are all ethers. Please note that I wrote the formula differently in order to emphasize the ether aspect. An answer giving those six structures can be found here.

Please note that there is no assignment regarding C5H12O. The information just above is for information purposes only.

Go to the Day Four Instructions for this lab.