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Wize University Chemistry Textbook > Lewis Structures & Resonance Structures

How to Draw Lewis Structures

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Drawing Lewis Structures

Drawing the "best" Lewis structure for a molecule is a great skill to have for your chemistry class! This concept will come in handy in the upcoming chapters as well. We will follow the steps below each time.

Wize Tip
Steps for Drawing Lewis Structures:

1) Calculate the total number of valence electrons for the molecule.
2) Write out all atoms, with the least electronegative atom in the middle (but H is never in the middle)
3) Connect all atoms with single bonds.
4) Put lone pairs on atoms, except H, until you run out of electrons. Put extra lone pairs on the central atom.
5) Shift lone pairs to make double or triple bonds to satisfy the Octet Rule and get the best formal charges.


Octet Rule: atoms need to have 8 electrons in the valence shell

Examples: C, N, O, F all need 8 electrons in their valence shell to have the "best" Lewis structure

Example: CF4 → the C atom has 8 valence electrons and each F atom has 8 valence electrons in the Lewis Structure


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Exceptions to the Octet Rule

Some elements are octet deficient (require less than 8 electrons in their valence shell)

Examples:
H and He can only have 2 electrons

Be can only have 4 electrons

In group 13, Al and B can only have 6 electrons

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Some elements have an expanded octet (can have more than 8 electrons in their valence shell)

Examples:
Non-metals in period 3 and onwards can have expanded octet.
P can have 10 electrons

S can have 12 electrons

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Some molecules like radicals have an odd number of electrons (these are rare!)

Example: NO
First let’s count the number of valence electrons (VE) in both atoms.
  • N →5 VEs
  • O → 6 VEs
  • So in total there are 11 VEs which is an odd number. We would be left with a molecule that looks like this:

Note: There is an unpaired electron on the N. This is called a radical molecule and is highly reactive so it is very short-lived.


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Formal Charges

The last thing we need to check to ensure we have the BEST Lewis Structure is to count formal charges.

Wize Concept
The best formal charge for an atom is zero.
If the formal charges for a molecule can't be 0 the best Lewis Structure for that molecule will have the lowest possible formal charges.

If formal charge is not zero, consider assigning negative formal charge to more electronegative elements and positive formal charges to less electronegative elements, if possible.

FC=VE−bonds connected to the atom - lone pair electrons on the atom\boxed{FC=VE - \text{bonds connected to the atom - lone pair electrons on the atom}}

FC is the formal charge of an atom
VE are the valence electrons the atom has

Example:
OF2


FC for F= 7 VE - 1 bond connected - 6 electrons on it
FC for F=7-1-6
FC for F=0

FC for O= 6 VE - 2 bonds connected - 4 electrons on it
FC for O= 6 - 2 - 4
FC for O=0
Therefore, we know this is the best possible Lewis structure!


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Example: Lewis Structures

Draw Lewis structures of the following molecules.

a) PCl3




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b) NH4+




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c) SeF4



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Example: Lewis Structure

Draw the Lewis Structure for SO42-



Determine the central atom. The central atom is usually the atom which has the lowest electronegativity. In this case it is S.


Count the total # of valence electrons.
6 (S) + [4 X 6 (O)] + 2= 32


Arrange the terminal atoms around the central atom.


Use e- to fill octets of terminal atoms.

Evaluate and rearrange electrons to find the best structure.




In our example all octets are satisfied but we have a 2+ on sulfur and negative charges on all oxygen atoms. To solve this we should move a l.p on oxygen (the negative element) to a double bond. Remember sulfur can expand its octet.

Practice: Formal Charges and Lewis Structures

Draw the Lewis structure of SO2Cl2 to answer the following questions.

Practice: Drawing Best Lewis Structures

Complete the “best” Lewis diagrams for the following species and use them to answer the next three questions

SeCl2



PO2+




AlI3





Which Lewis diagram has double bond(s)?
Extra Practice
Practice: Formal Charge
Practice: Formal Charges
In the molecule POCl3, what is the formal charge on the P atom in the best Lewis structure?
Acids and Bases: Acids and Salts
Draw the correct lewis structure of HClO3 and draw all resonance structures.
Lewis Structures
Calculate the formal charge on each atom in the molecule. Determine the most stable resonance structure.
Lewis Structures
Calculate the formal charge on each atom in the molecule. Determine the most stable resonance structure.
Lewis Structures: Resonance
Starting from the Lewis structure below, draw all valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures: Resonance
Inspect the following incomplete resonance structures, and identify the INCORRECT statement about the
nitrous oxide molecule.
Hybridization, bond angle
1. What are the hybridization of each of the N atom in N3― and what is the NNN bond angle?
2. What are the hybridization of each of the atoms in HOCN? What are the HOC and OCN bond angles?
Choose the correct option:
Lewis Dot Structure, Resonance
Choose the most stable resonance form of carbon monoxide.
Resonance Structure, Oxidation State
Choose the correct statement:
Practice: Formal Charge
Practice: Formal Charges
In the molecule POCl3, what is the formal charge on the P atom in the best Lewis structure?
Lewis Structures
Complete the “best” Lewis diagrams for the following species and use them to answer the next three questions
SeCl2
PO2+
Covalent Bonding and Lewis Structures
Draw Lewis structures for the following molecules
a) NH3
b) CO2
Lewis Structure: Geometry Practice
Three compounds are given below. Write the dot structure and draw the molecular geometry for each of these molecules. Also include a descriptive name to describe the molecular shape: bent, T-shaped, see-saw, trigonal planar, trigonal pyramid, trigonal bipyramid, square planar, square pyramid, tetrahedral, or octahedral.
Lewis Structures: Resonance
Show all of the most stable resonance structures for CO32-.
Lewis Structures
Draw the Lewis Structure for SF2O2.
Lewis Structures
Draw the Lewis structure for CH2Br2
Lewis dot structure
Which of the following statements is (are) correct for the most important Lewis structure of BCl3?
Lewis dot structure
Draw the best Lewis dot structure of CN–.
Hybridization
Consider the following Lewis Dot Structure of CO:
What is the best option for describing the bond between C and O?
Lewis Dot Structure
Draw Lewis dot structures and more stable resonance structures (wherever applicable) of the following:
1. NO2
2. CH3OH
Benzene Derivatives
Complete the best Lewis structure of p-aminosalicylic acid (C7H7NO3) below to answer the following questions.
a) How many valence electrons are in the complete Lewis structure?
b) What is the formal charge on the nitrogen atom?
Benzene Derivatives
For the skeletal structure below, complete the Lewis structure and draw all three resonance structures for phenolate, C6H5O-. Show all lone pairs and additional bonds.
Lewis structure: Formal charge
Complete the best Lewis structure of the organic compound shown below (CH3CH2NO2). Determine the formal charge on the nitrogen.
Acids and Bases: Acids and Salts
Draw the correct lewis structure of chloric acid and draw all resonance structures.
Lewis Structure: Electron Movement in Resonance Structures
Complete the resonance structures by drawing the curly arrows required to convert between one resonance structure to another. Circle the resonance structure that is lower in energy.
ClO2-:
Lewis Structure: Resonance Structures
How many Resonance structures are there for the sulfite ion?
Organic Compounds
Complete the Lewis structure of p-chlorobenzoate (shown below) to answer the following questions.
Organic Compounds
Complete the correct Lewis structure of NH3CH3CH3CO2 (see below) to answer the following questions.
Resonance Structures
Draw all the resonance structures of CO2Cl- to answer the following questions.
Lewis Structures
Draw the correct Lewis structure of CO to answer the following questions.
Lewis Structures
Draw the correct Lewis structure of XeF5 to answer the following questions.
Organic Compounds
Complete the Lewis structure of p-chlorobenzoate (shown below) to answer the following questions.
Organic Compounds
Draw all the resonance structures of aniline (NH2C6H5). The incomplete Lewis structure of aniline is shown below.
Organic Compounds
Complete the correct Lewis structure of NH3CH3CH3CO2 (see below) to answer the following questions.
Organic Compounds
Draw the correct Lewis structure of HCCH.
Acids and Salts
Draw the correct Lewis structure of potassium sulfite (Na2SO3) and phosphoric acid (H3PO4).
Resonance Structures
Draw all the resonance structures of CO2Cl- to answer the following questions.
Resonance Structures
Draw all resonance structures for the carbonate ion: CO32-.
Lewis Structures
Draw the correct Lewis structure of CO to answer the following questions.
Lewis Structures
Draw the correct Lewis structure of XeF4 to answer the following questions.
Lewis Structures
Draw the correct Lewis structure of XeO4 to answer the following questions.
Lewis Structures
Draw the correct Lewis structure of BeF2.
Lewis Structures
Draw the Lewis structure of SO2Cl2 to answer the following questions.
Lewis Structures
Complete the “best” Lewis diagrams for the following species and use them to answer the next three questions
a) SeCl2
b) PO2+
Lewis Structures
Which is the correct Lewis Structure forAlCl3\rm AlCl_3?
VSEPR: Molecular Polarity
Is SO2 polar or non-polar?
What is the molecular shape?
What is the electron geometry?
Lewis Structures: VSEPR
Which of the following compounds of xenon has exactly one nonbonding pair of electrons on the xenon
atom?
Lewis Structures
Which one of the following ions has nonbonding valence electrons at the central atom?
Lewis Structures: Resonance
Inspect the following incomplete resonance structures, and identify the INCORRECT statement about the
nitrous oxide molecule.
Lewis Structures
Next question concerns the molecule acrylonitrile, C3H3N, shown below.
How many nonbonding valence electrons are there in a molecule of acrylonitrile?
Lewis Structures
Complete the skeleton given below to give the “best” Lewis diagram for a molecule of H2CCHCH2C(O)OH, then identify which of the statements below is false?
A. The C3C4 bond is stronger than the C2C3 bond.
B. There are 8 electrons not involved in bonding.
Lewis Structures: Formal Charge
In the molecule POCl3, what is the formal charge on the P atom in the best Lewis structure?
Lewis Structures: Molecular Polarity
Draw Lewis structures and give the other information requested for the following:
NO3-. Polar or nonpolar molecule?
BrF5. Polar or nonpolar molecule? Geometry?
Lewis Structures: Formal Charge
5) Which of the following is the best Lewis structure for CO? (Enter a b c or d as your answer)
Lewis Structure: Phosphorus Pentafluoride
Please draw a reasonable Lewis structure for PF5
Lewis Structure: Nitric Oxide
Please draw the BEST Lewis structure for NO.
Lewis Structures
Draw Lewis structures, including resonance structures where applicable, for the following compound: PF5
Lewis Structure: Sulphate
Draw a reasonable Lewis structure for SO42-.
How many non-bonding electron pairs are on the central atom in PF4+PF_4^+ ?
Lewis Structure: Alkene
Which of the following molecules contains a double bond? (May be more than one)
a) HCCBr
b) H2NNH2
Lewis Structures
Calculate the formal charge on each atom in the molecule. Determine the most stable resonance structure.
Lewis Structures: Formal Charge
In the molecule POCl3 the central atom is P, what is the formal charge on the P atom in the best dot
structure (Lewis structure)?
(Note: Phosphorous is a third row element.)
Lewis Structures
Draw the Lewis structure for HCN. Calculate the formal charge of each atom.
Lewis Structures: Formal charge
Which of the following structures has a Cl with +1 formal charge?
Lewis Structure
Draw the Lewis structure for BFClH.
How to Draw a Lewis Structure Question
1) Draw the Lewis structure of H3PO4.
1) Complete the Lewis structure for the skeletal structure shown below
Lewis Structures: Formal charges
Complete the following skeletal structure. Please show all lone pairs and formal charges.
How many lone pairs are there in the best Lewis structure
Lewis Structure: Formal charge
Complete the following skeletal structure. Please show all lone pairs and formal charges.
Lewis Structures: Formal Charge
In the molecule POCl3, what is the formal charge on the P atom in the best Lewis structure?
VSEPR and Lewis Structure
1) Draw Lewis structures for the following molecules
2) List the molecular shape and electron geometry for each
a) NH3
Which of the following gives a pair of valid Lewis structures that are resonance structures of each other?
A. i only
B. ii only
Lewis Structures
Which of the following are correct, “best”, Lewis diagrams for
the condensed formulae given below them?
A. i only
Lewis Structures: VSEPR
If a molecule has the formula XBr4−\text{XBr}_ 4^- with a see-saw molecular geometry, what is the best choice for the identity of XX?
Lewis Structures
The Lewis diagrams for several molecules are shown below. Which of the molecules would be nonpolar?
Molecular Polarity and VSEPR
Consider the best Lewis diagrams for the following chemical species to answer the next two questions
CℓF3
O3
Lewis Structures
Complete the “best” Lewis diagrams for the following species and use them to answer the next three questions
a) SeCℓ2
b) PO2+
Lewis Structures
Draw Lewis structures for the following molecules.
a) AlCl3 b) CHCl3 c) PO43- d) PO33-
Practice: Skeletal Structure 2
Complete the following skeletal structure. Please show all lone pairs and formal charges.
Practice: Lewis Structure of Sulphate
Draw a reasonable Lewis structure for SO42-.
Draw Lewis structures, including resonance structures where applicable, for the following compound: NO3-
Lewis Structures: Resonance
Draw all reasonable resonance structures for the following compounds.
a) PS2Cl2-
b) SO42-
Lewis Structures: Resonance
Starting from the Lewis structure below, complete two other valid resonance structures. Show all bonds, lone pairs, and non-zero formal charges.
Lewis Structures
Complete the following skeletal structure. Please show all lone pairs and formal charges.
Draw Lewis structures, including resonance structures where applicable, for the following compound: XeF6
Lewis Structure: Resonance
Diazomethane is a poisonous, explosive yellow gas at room temperature!
Starting its Lewis structure which is given below, show two other valid resonance structures. Be sure to show all bonds, lone pairs, and formal charges.
Which of these elements is the central atom in CHBrClI?
Draw Lewis structures, including resonance structures where applicable, for the following compound: XeF6
Which is the correct geometry of the following compounds: PBr3, BH4-, NMe4+