Lewis Structure of PO3- (With 6 Simple Steps to Draw!)

Ready to learn how to draw the lewis structure of PO3- ion?

Awesome!

Here, I have explained 6 simple steps to draw the lewis dot structure of PO3- ion (along with images).

So, if you are ready to go with these 6 simple steps, then let’s dive right into it!

Lewis structure of PO3- ion contains one double bond and two single bonds between the Phosphorous (P) atom and Oxygen (O) atoms. The Phosphorus atom (P) is at the center and it is surrounded by 3 Oxygen atoms (O). 

Let’s draw and understand this lewis dot structure step by step.

(Note: Take a pen and paper with you and try to draw this lewis structure along with me. I am sure you will definitely learn how to draw lewis structure of PO3- ion).

6 Steps to Draw the Lewis Structure of PO3-

Step #1: Calculate the total number of valence electrons

Here, the given ion is PO3^–. In order to draw the lewis structure of PO3^– ion, first of all you have to find the total number of valence electrons present in the PO3^– ion.
(Valence electrons are the number of electrons present in the outermost shell of an atom).

So, let’s calculate this first.

Calculation of valence electrons in PO3^– ion

• For Phosphorus: 

Phosphorus is a group 15 element on the periodic table. ^[1]

Hence, the valence electrons present in phosphorus is 5 (see below image).

• For Oxygen:

Oxygen is a group 16 element on the periodic table. ^[2]

Hence, the valence electron present in oxygen is 6 (see below image).

Hence in a PO3^– ion, 

Valence electrons given by Phosphorus (P) atom = 5
Valence electrons given by each Oxygen (O) atom = 6
Electron due to -1 charge, 1 more electron is added
So, total number of Valence electrons in PO₃^– molecule = 5 + 6(3) + 1 = 24

Step #2: Select the center atom

While selecting the center atom, always put the least electronegative atom at the center.

(Remember: Fluorine is the most electronegative element on the periodic table and the electronegativity decreases as we move right to left in the periodic table as well as top to bottom in the periodic table). ^[3]

Here in the PO3- ion, if we compare the phosphorus atom (P) and oxygen atom (O), then phosphorus is less electronegative than oxygen.

So, phosphorus should be placed in the center and the remaining 3 oxygen atoms will surround it.

Step #3: Put two electrons between the atoms to represent a chemical bond

Now in the above sketch of PO3, put the two electrons (i.e electron pair) between each phosphorus atom and oxygen atom to represent a chemical bond between them.

These pairs of electrons present between the Phosphorus (P) and Oxygen (O) atoms form a chemical bond, which bonds the phosphorus and oxygen atoms with each other in a PO3- ion.

Step #4: Complete the octet (or duplet) on outside atoms. If the valence electrons are left, then put the valence electrons pair on the central atom

Don’t worry, I’ll explain!

In the Lewis structure of PO3^– ion, the outer atoms are oxygen atoms.

So now, you have to complete the octet on these oxygen atoms (because oxygen requires 8 electrons to have a complete outer shell).

Now, you can see in the above image that both the oxygen atoms form an octet.

Also, all the 24 valence electrons of PO3- ion (as calculated in step #1) are used in the above structure. So there are no remaining electron pairs.

Hence there is no change in the above sketch of PO₃^– ion.

Let’s move to the next step.

Step #5: Check whether the central atom has octet or not. If it does not have an octet, then move the electron pair from the outer atom to form a double bond or triple bond

In this step, we have to check whether the central atom (i.e phosphorus) has an octet or not. 

In simple words, we have to check whether the central Phosphorus (P) atom is having 8 electrons or not.

As you can see from the above image, the central atom (i.e phosphorus) has only 6 electrons. So it does not fulfill the octet rule.

Now, in order to fulfill the octet of phosphorus atom, we have to move the electron pair from the outer atom (i.e oxygen atom) to form a double bond.

Now you can see from the above image that the central atom (i.e phosphorus), is having 8 electrons. So it fulfills the octet rule and the phosphorus atom is stable.

Step #6: Check the formal charge

Now, you have come to the final step and here you have to check the formal charge on PO3- ion. 

For that, you need to remember the formula of formal charge;

Formal charge = Valence electrons – Nonbonding electrons – (Bonding electrons)/2

• For Phosphorus:
  Valence electrons = 5 (as it is in group 15)
  Nonbonding electrons = 0
  Bonding electrons = 8

• For double bonded Oxygen:
  Valence electron = 6 (as it is in group 16)
  Nonbonding electrons = 4
  Bonding electrons = 4

• For single bonded Oxygen:
  Valence electron = 6 (as it is in group 16)
  Nonbonding electrons = 6
  Bonding electrons = 2

Formal charge	=	Valence electrons	–	Nonbonding electrons	–	(Bonding electrons)/2
P	=	5	–	0	–	8/2	=	+1
O (double bonded)	=	6	–	4	–	4/2	=	0
O (single bonded)	=	6	–	6	–	2/2	=	-1
O (single bonded)	=	6	–	6	–	2/2	=	-1

Let’s keep these charges on the atoms in the above lewis structure of PO3^– ion.

As you can see in the above sketch, the pair of positive and negative charges gets canceled. Thus there is only one -ve charge left on the oxygen atom, which indicates the -1 formal charge on the PO3 molecule.

Hence, the above lewis structure of PO3- ion is the stable lewis structure.

Each electron pair (:) in the lewis dot structure of PO3- ion represents the single bond ( | ). So the above lewis dot structure of PO3- ion can also be represented as shown below.

Related lewis structures for your practice:
Lewis Structure of BBr3
Lewis Structure of IF2-
Lewis Structure of BrF2-
Lewis Structure of P2
Lewis Structure of IBr2- 

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