Chem 1025 Lewis Structure Lab

Chem1025C Lewis Structure Lab

Lewis Structures for Covalently Bound Species

Lewis Structure Activity:

This lab will be examining covalently bound structures: molecules and polyatomic ions. In
class we have been working on drawing Lewis structures. Lewis structures are two-
dimensional drawings of covalently bonded species. On paper these molecules look very
different from their three-dimensional structures. Molecular shape of the species is one of
the properties we can determine from the Lewis structure. In this lab we will practice
drawing two-dimensional Lewis structures and then look at these structures transformed
into three dimensions. You will use both a simulation and the spice drops and toothpicks
found in your lab kit.

We will be using the octet rule when drawing the Lewis structures: atoms in a compound
lose, gain, or share electrons in order to achieve a stable noble gas configuration.

Prepare your notebook. When the lab is complete your lab notebook should include the
following:

1. Enter Lewis Structure Model Lab into Table of Contents.
2. Write the title of the lab on the top of the page.
3. Date/number the page (if you work on it over a few days, date each time you are

working). Sign in your lab notebook each time you stop working.
4. Record the Purpose of Experiment in your own words. Remember the purpose is the

overall question that will be answered by collecting the data and doing any
requested calculations.

5. Indicate PPE (personal protection equipment) required while performing the lab:
none

6. Prepare tables as shown below in the lab report format.
7. You will need to upload the pictures of your “spice drop” molecules created in Part B

into Canvas with your lab notebook

Lab Report Format:
Create six tables in your lab notebook. For each compound in the list, include the following:

Lewis Structure VSEPR drawing Electron Pair

Geometry
Molecular
Geometry

Bond angles
(from simulator
in Part C)

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Materials needed:
Spice drops and toothpicks from lab kit
VSEPR Handout in lab module in Canvas
Structure Simulation link in lab module in Canvas

A. Drawing Lewis Structures:

1. Draw the Lewis structures in your lab notebook for the following six covalently
bound species: CO2, CH2O, PCl3, CO32-, H2O, O3

2. General Guidelines for drawing Lewis structures:
a. Determine the total number of valence electrons available for bonding by

adding the valence electrons for all of the atoms. For main group
(Representative elements) the valence electrons are the same as their group
number. Charges affect the number of electrons available. For anions, add the
charge to the total valence electrons and for cations, subtract the charge from
the total electrons.

b. Draw the skeletal arrangement of atoms. Determine the central atom and
connect each atom with a single bond. H can only form one bond and can
never be a central atom.

c. Subtract the number of electrons used to form the single bonds from the total
determined in (a).

d. Using the remaining electrons add lone pairs to each atom to complete their
octet. Always start with the periphery atoms. After completing the octets of
the periphery atoms, place any remaining electrons on the central atom.
Remember you cannot use more electrons than calculated in (a).

e. If the central atom does not have an octet, use a lone pair from a periphery
atom and create a double or triple bond as needed.

B. Use of spice drops and toothpicks models:

1. Do not eat the spice drops. They have been stored in a chemical environment and
are not considered edible. If you prefer, and have it on hand, you may substitute
playdough or modelling clay.

2. Each center is a spice drop. These will allow us to firmly hold the toothpicks. The
color is not important when building the structure. It is recommended that you
snap the toothpicks in half. The shorter picks molecules are easier to manipulate
and display for photos.

3. Each toothpick represents a bonding pair.
4. Using your Lewis Structures and the VSEPR handout determine the electron pair

geometry. This geometry identifies the arrangement of all of the electrons around
the central atom, and includes both lone pairs and bonding pairs. Then name the
molecular geometry of each of these molecules. The molecular geometry identifies
the arrangement of the bonds and will be different from the electron pair geometry
if the central atom has a lone pair of electrons. Record the electron pair geometry,
molecular geometry in the data table.

5. Sketch the VSEPR drawing in the data table. This drawing should represent the
shape.

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6. Using the spice drop and toothpicks assemble the molecule to represent the shape
determined from the Lewis structure. When you have assembled the molecule,
take a picture. Upload these with your lab notebook in Canvas. You can put more
than one molecule in a picture.

C. PhET Molecular Shape Simulator:
1. Use the simulator to recreate your Lewis structures. The link is found in the lab

module in Canvas. You can verify your electronic and molecular geometries
determined from the VSEPR handout. Use the simulator to determine the bond
angles and record them in your data table.

Works cited: Mullins, N.J., & Milczanowski, S.E. (2020). Lab Manual for Introductory Chemistry
CHM1025C/CHM1032C. Jacksonville: FSCJ Copy Center.

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