HOW TO DRAW
LEWIS STRUCTURES!
A STEP BY STEP TUTORIAL
Kyla Smart
Michael Burnette
Nick Ryan Lor
Ross Sison
So…what are Lewis
Structures?
Lewis Diagrams are used to describe
the structure of covalent molecules.
They use a simple and clear notation
to represent the valence shell electrons
of all of the atoms in a molecule.
How to Create a Lewis
Structure
Step 1.
Add up the number of valence electrons present in
all of the atoms in the molecule.
To determine how many valence electrons an
atom has you can use the periodic table. The
number of valence electrons is equal to the group
number of the element.
Tip: To move faster you can multiply the group
number of the element with the number of atoms
of that element in the molecule
Example: Step 1
Assignment: Draw a Lewis structure of the
molecule O3
There are 3 oxygen atoms
Oxygen is found in group 6
Therefore Oxygen has 6 valence electrons
3 X 6 = 18
There are 18 valence electrons in O3
Step 2.
Draw a rough structure
Pick a central atom and connect the remaining
atoms with a single bond to the central atom
The central atom is usually the first atom in the
molecule
Example Step 2.
O-O-O
Step 3.
Place dots around all of the atoms.
These dots represent unpaired valence electrons
A single bond accounts for 2 valence electrons
Make sure that each atom has 8 valence electrons
around it
(there are a few exceptions to this rule such as
Hydrogen)
Example Step 3.
O-O-O
Represents the valence electrons
Step 4
Count up the number of electrons present in the
atom
Each bond represents 2 electrons
Check to make sure that this number is equal to
the number determined at the beginning
If it matches, then YOU’RE DONE
If not, move on to step 5
Example Step 4.
O-O-O
There is a total of 20 valence electrons in this
diagram.
In step 1 we decided that there needed to be 18
valence electrons .
This diagram has 2 extra valence electrons
Step 5
To lower the total number of electrons, take 2 electrons off
of two atoms that are bonded together and place another
bond between those two atoms.
Each time you do this, it will lower your electron count by
2
Do this until the number of electrons is equal to the
number determined in step 1.
Make sure that the molecule is as symmetrical as possible.
For example, do not have a triple bond and a single bond
when you could have a two double bonds
Example Step 5.
O-O=O
Remove a pair of valence electrons from the
central atom
Remove a pair of electrons from one of the outer
atoms
The two atoms that you have removed the
electrons from are now sharing, not one but two
pairs of electrons and therefore are double
bonded
The diagram now
has 18 valence
electrons
Congratulations,
this number
matches the
number from step
1.
A Helpful Hint
2
1
3
4
HONC
Halogens/Hydroge
n
Oxygen
Nitrogen
Carbon
This diagram can help you remember the number of bonds that
each atom tends to form.
Hydrogen & Halogens tend to form 1 bond
Oxygen tends to form 2 bonds
Nitrogen tends to form 3 bonds
Carbon will form 4 bonds (with some exceptions)
Also…
If your compound has a charge on it (aka is an
ion), add up the total number of electrons present
and either add extra electrons if you have a
negative charge or subtract electrons if you have a
positive charge
Draw the structure of the compound so that the
total number of bonds and lone pairs adds up to
the correct amount of electrons
Draw brackets to the left and right of the Lewis
Structure and put its charge to the right of the top
of the right bracket
Example
NO3
O=N O
O
YOU’RE DONE!