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POGIL Activity: Lewis Structures and Drawing Bonds
Why? READ THIS!
We will learn there are polar and nonpolar covalent compounds. In polar covalent compounds there is an
unequal sharing of electrons between atoms, whereas in nonpolar covalent compounds there is an
equal/almost equal sharing of electrons between atoms. In addition to determining polarity based upon
electronegativities, we can determine the polarity based upon structural drawings.
The polarity of a compound can tell us a lot about the properties of a certain compound, so learning how
to determine the polarity will be helpful. However, we must first learn how to draw the compounds in
order to determine bond polarity. In addition, we can take the structural formula of the compound and
determine the 3-D shape of the compound.
Model 1: Lewis Structures of Elements
You learned about Lewis structures in the previous chapter. Lewis structures are used to represent the
valence electrons around the element. You must be able to draw the Lewis structure of any main group
element before you can draw the Lewis structure of a compound.
Again, here are the steps for drawing Lewis structures (Electron Dot Diagram) for elements:
1. Write the symbol for the element
2. Determine the number of valence electrons the element has
3. Draw the valence electrons as dotes surrounding the element
a. We designate 4 sides to the element symbol: top, right, bottom, left
b. Before you can put two dots on the same side, each side must have one dot (2 max)
Questions:
1. Draw the Lewis structures (Electron Dot Diagram) for the following elements:
a. Ca
b. P
c. H
d. C
e. Cl
Model 2: Lewis Structures and Structural Formulas of Single Bonds
Now that you remember how to draw Lewis structures for individual elements, let’s draw the Lewis structures
for compounds. The Lewis structures of compounds use straight lines to represent the two shared electrons
in a bond. The structural formulas can then be used to draw the 3-D structures of covalent compounds.
In covalent compounds with single bonds, there is only one shared pair of electrons between the central
atom and the other atoms.
Example: Water (H2O)
Molecular Formula
Electron Dot Diagram
Lewis Structure
H2O
Total Valence Electrons = 8
NOTE: Hydrogen is full at 2 valence electrons!
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Practice #1: Draw the Lewis structures for the elements in the compound, methane (CH4).
Follow these steps:
1. Gather information
a. Count the number of valence electrons (you can’t end up with more or less than that!)
Example: chloroform ( CHCl3)
# C: ____
# H: ______
# Cl: _____
Draw the Electron Dot Diagram
for each element in the formula:
*How many total valence electrons are represented between the C, H, and Cl atoms? _____
Action: Obtain the same number of cheerios to represent the valence electrons.
b. Determine the central atom (least electronegative: typically the first element in formula)
i. If carbon is in the compound, it will be in the center since it has the most bonding
sites or single electrons.
ii. If carbon is not in the compound, the less electronegative element is the central atom
iii. Hydrogen and halogens only have one bonding site so they are on the end
*The central atom is: _____________
2.
Action: Using cheerios, arrange the atoms to show how the atoms bond in the molecule around the
central atom.
a. Match single electrons up between atoms
Draw your Model
i. FIRST: Shared bonding electrons pair up as between the 2
atoms
that form the bond.
ii. SECOND: Add remaining valence electrons as Lone pairs
(doubled up electrons in Lewis structures) that do not participate
in bonding.
1. Remember that Hydrogen is full at 2 electrons and
can never have lone pairs.
3. Draw the Bonds
Lewis Structure
4.
Verify the Structure
a. Circle the shared electrons between carbon and each hydrogen.
b. Replace each pair of dots that represents a shared pair of electrons with a
dash(or bar) in the box to the left.
c. This is the Lewis Structure of methane (CH4)
d. How many electrons does each dash represent? _____
a. Count the number of valence electrons surrounding each atom
b. All atoms should have OCTET, 8 valence electrons, except H, Be, & B
c. # of valence e- should be the same as step 1
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Together: Another example for PF3
Compound
Electron Dot
Date:
Period:
Lewis Structure
1. PF3
Total # of Valence e-: _____
Single-Bonded Structures:
Complete the following Lewis Structures and Structural Formulas for the following Single Bonds.
Compound
Electron Dot
Lewis Structure
1. H2S
Total # of Valence e-: _____
2. HF
Total # of Valence e-: _____
3. SCl2O
Total # of Valence e-: _____
Your group will check your answers with the instructor before moving on.
Model 3: Lewis Structures and Structural Formulas of Multiple Bonds
Multiple bonds are formed when the central atom has not achieved octet (8 valence electrons) and
there no more valence electrons available. Exterior atoms are forced to share an additional pair of
electrons, forming a double or triple, to fulfill the central atom’s need for 8 valence electrons.
 Use the same steps as single bonds.
 You cannot break apart lone pairs of electrons and leave a single electron alone.
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Double Bond: A covalent bond that involve sharing two pairs of electrons
Example: O2
Triple Bond: Covalent bond formed when atoms in the bond share three pairs of electrons
Example: N2
Multiple-Bonded Molecules:
Draw the Lewis Structure and Structural Formulas of the compounds below with Multiple Bonds.
Compound
Electron Dot Diagram
Lewis Structure
1. CO2
Total # of Valence e-: _____
2. HCN
Total # of Valence e-: _____
3. H2CO
Total # of Valence e-: _____
Your group will check your answers with the instructor before moving on.
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Date:
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Questions
1) How many electrons are shared between 2 atoms to form a covalent bond? ____________
2) How do you determine the number of electrons available in a molecule to draw a Lewis
Structure?
3) How many electrons would be available in the Lewis structure for the molecule, methanol
(CH3OH)?
4) Polyatomic ions are covalently bonded atoms with a net charge. The net charge is included
in the number of available electrons.
a. If the polyatomic ion has a positive one (+1) charge, how would the number of
available electrons change?
b. If the polyatomic ion has a negative two (-2) charge, how would the number of
available electrons change?
5) Identify the number of available electrons in the following molecules. Draw the Lewis
Structure.
Molecule
Lewis Structure
a) HBr
Total # of Valence e-: _______
b) OH -1
Total # of Valence e-: _______