How to calculate formal charge using formal charge formula

 In this post,I am going to show you how to calculate formal charge of each atom from a Lewis structure using the formal charge formula.

How to calculate formal charge using formal charge formula
How to calculate formal charge using formal charge formula


To find the formal charge of a atom from a Lewis structure,you need to apply the following formal charge formula or equation:

●Formal charge = Valence electrons in neutral atom - 1/2 (Bonding Electrons) - Nonbonding electrons

Formal charge formula or equation



To use the above formal charge formula,at first you need to calculate the number of valence electrons in a free atom,then you need to calculate the number of nonbonding electrons and at last you need to consider the half of the bonding electrons.

Here is an example that will help you to understand how to calculate the formal charge of an an using formal charge formula.



Consider the best Lewis structure of CO2 molecule.Here you need to calculate the formal charge of oxygen atom and carbon atom.

How to calculate formal charge
How to calculate formal charge


Formal charge of O atom in CO2:

●The number of valence electrons in a neutral oxygen atom is 6 as it is the element of group VIA.
●Nonbonding electrons of O is 4.

●Bonding electrons of O is 4.

Formal charge of O = Valence electrons in neutral O atom - 1/2 (Bonding Electrons of O) -Nonbonding elctrons of O

               =6  - 1/2(4) - 4

                =6 -2 -4
                  =6-6
                   =0
So,the formal charge of O atom in CO2 best Lewis structure is 0.Since the second O atom is in the same electronic environment,it's formal charge also will be zero. 


Formal charge of C atom in CO2:

●The number of valence electrons in a neutral carbon atom is 4 as it is the element of group IVA.
●Nonbonding electrons of C is 0.

●Bonding electrons of C is 8.

●Formal charge of C = Valence electrons in neutral C atom - 1/2 (Bonding Electrons of C) - Nonbonding elctrons of C

               =4 - 1/2(8) - 0

                =4-4
                  =0
So,the formal charge of C atom in CO2 best Lewis structure is 0.

Now if you add  the formal charge of each atom,you will get (0+0+0=0) zero.This means that CO2'overall charge is zero.

Here is the another formula for calculating the formal charge of atoms from a Lewis structure.

Formal Charge=Valence Electrons -Dots - Lines


Formal charge of O atom in CO2:

●The number of valence electrons in a neutral oxygen atom is 6 as it is the element of group VIA.
●Dots electrons of O is 4.

●Lines or bonds of O is 2.

Formal charge of O = Valence electrons in neutral O atom -Dots - Lines

= 6 - 4 - 2
= 6 -6
=0

So,the formal charge of O atom in CO2 best Lewis structure is 0.Since the second O atom is in the same electronic environment,it's formal charge also will be zero. 


Formal charge of C atom in CO2:

●The number of valence electrons in a neutral carbon atom is 4 as it is the element of group IVA.
●Dots electrons of C is 0.

●Lines or bonds of C is 4.

Formal charge of C = Valence electrons in neutral C atom -Dots - Lines

= 4 - 0 - 4
= 4 -4
=0

Here is the second example that will help you to understand how to calculate the formal charge of atoms in a Lewis structure.

Consider the best Lewis structure of H2O.
Or,


To calculate the formal charge of a atom from H2O Lewis structure,you need to apply the following formal charge formula:

●Formal charge = Valence electrons in neutral atom - 1/2 (Bonding Electrons) - Nonbonding elctrons

Formal charge of H atom in H2O:

●The number of valence electrons in a neutral H atom is 1 as it is the element of group IA.
●Lone pairs of electrons of H is 0.

●Bonding electrons of H is 2.

Formal charge of H = Valence electrons in neutral H atom - 1/2 (Bonding Electrons of H) - Nonbonding elctrons of H

               =1 - 1/2(2) - 0

                =1 -1 - 0
                  
                   =0
So,the formal charge of H atom in H2O best Lewis structure is 0.Since the second H atom is in the same electronic environment,it's formal charge also will be zero. 


Formal charge of O atom in H2O:

●The number of valence electrons in a neutral O atom is 6 as it is the element of group VIA.
●Lone pairs of electrons of O is 4.

●Bonding electrons of O is 4.

Formal charge of O = Valence electrons in neutral O atom - 1/2 (Bonding Electrons of O) - Nonbonding elctrons of O

               =6 - 1/2(4) - 4

                =6 -2 - 4
                  =6-6
                   =0
So,the formal charge of O atom in H2O best Lewis structure is 0.


Now if you add  the formal charge of each atom,you will get (0+0+0=0) zero.This means that H2O'overall charge is zero.

Here is the another formula for calculating the formal charge of atoms from H2O Lewis structure.

Formal Charge=Valence Electrons -Dots - Lines
           
      Formal charge of H atom in H2O:

●The number of valence electrons in a neutral H atom is 1 as it is the element of group IA.
●Dots electrons of H is 0.

●Lines or bonds of H is 1.

Formal charge of H = Valence electrons in neutral H atom -Dots - Lines

= 1 - 0 - 1
= 1 - 1
=0

So,the formal charge of H atom in H2O best Lewis structure is 0.Since the second H atom is in the same electronic environment,it's formal charge also will be zero. 

Formal charge of O atom in H2O:

●The number of valence electrons in a neutral oxygen atom is 6 as it is the element of group VIA.
●Dots electrons of O is 4.

●Lines or bonds of O is 2.

Formal charge of O = Valence electrons in neutral O atom -Dots - Lines

= 6 - 4 - 2
= 6 -6
=0

 

Here is the third example to calculate the formal charge from the CO Lewis Structure.


To find the formal charge of C and O atom from CO Lewis structure,you need to apply the following formal charge formula:

●Formal charge = Valence electrons in neutral atom - 1/2 (Bonding Electrons) - Nonbonding electrons



Consider the best Lewis structure of CO molecule.Here you need to calculate the formal charge of oxygen atom and carbon atom.

Best CO Lewis Structure


Formal charge of O atom in CO:


●The number of valence electrons in a neutral oxygen atom is 6 as it is the element of group VIA.
●Number of Nonbonding electrons of O is 2.

●Number of bonding electrons of O is 6.

Formal charge of O = Valence electrons in neutral O atom - 1/2 (Bonding Electrons of O) - Nonbonding electrons of O 

               =6 - 1/2(6) - 2

                =6 -3 -2
                  =6-5
                   =+1
So,the formal charge of O atom in CO best Lewis structure is +1. 


Formal charge of C atom in CO:

●The number of valence electrons in a neutral carbon atom is 4 as it is the element of group IVA.
●Number of nonbonding electrons of C is 2.

●Bonding electrons of C is 6.

●Formal charge of C = Valence electrons in neutral C atom - 1/2 (Bonding Electrons of C) - Nonbonding elctrons of C

               =4 - 1/2(6) - 2

                =4 - 3 -2
                    =4 -5
             =-1
So,the formal charge of C atom in CO best Lewis structure is -1.

Now if you add  the formal charge of each atom,you will get {(-1)+(+1)=0} zero.This means that CO'overall charge is zero.
How to calculate the formal charge of C and O in CO Lewis Structure

How to calculate the formal charge of C and O in CO Lewis Structure




Here is the another formula for calculating the formal charge of C and O atoms from the CO Lewis structure.



Formal Charge=Valence Electrons -Dots - Lines




Formal charge of O atom in CO:

●The number of valence electrons in a neutral oxygen atom is 6 as it is the element of group VIA.
●Dots electrons of O is 2.

●Lines or bonds of O is 3.

Formal charge of O = Valence electrons in neutral O atom -Dots - Lines

= 6 - 2 - 3
= 6 -5
=+1

So,the formal charge of O atom in CO best Lewis structure is +1. 


Formal charge of C atom in CO:

●The number of valence electrons in a neutral carbon atom is 4 as it is the element of group IVA.
●Dots electrons of C is 2.

●Lines or bonds of C is 3.

Formal charge of C = Valence electrons in neutral C atom -Dots - Lines

= 4 - 2- 3
= 4 - 5
=-1

So,the formal charge of C atom in CO best Lewis structure is -1.

Summary:

The formal charges of C and O in the best CO Lewis Structure is -1 and +1.





 



                
                                 






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