Lewis structure of PO43-

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The Lewis structure of PO₄^3- contains one double bond and three single bonds, with phosphorus in the center, and four oxygens on either side. The left oxygen atom has two lone pairs. The right oxygen atom, top oxygen atom, and bottom oxygen atom have three lone pairs, and the phosphorus atom does not have any lone pair.

Plus, there is a negative (-1) charge on the right oxygen atom, top oxygen atom, and bottom oxygen atom.

Steps

By using the following steps, you can easily draw the Lewis structure of PO₄^3-:

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Calculate formal charge and check stability (if octet is already completed on central atom)
#5 Convert lone pair and calculate formal charge again (if formal charges are not closer to zero)

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… phosphorus is a group 15 element and oxygen is a group 16 element. Hence, phosphorus has five valence electrons and oxygen has six valence electrons.

Now PO₄^3- has one phosphorus atom and four oxygen atoms.

So the total number of valence electrons = valence electrons of phosphorus atom + (valence electrons of oxygen atom × 4)

And PO₄^3- has a negative (-3) charge, so we have to add three more electrons.

Therefore, the total number of valence electrons = 5 + 24 + 3 = 32

• Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for phosphorus and oxygen as follows:

Electronegativity value of phosphorus = 2.19
Electronegativity value of oxygen = 3.44

Obviously, phosphorus is less electronegative than oxygen. Hence, assume that phosphorus is the central atom.

So now, put phosphorus in the center and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of PO₄^3- something like this:

Also read: How to draw Lewis structure of HCl (4 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since phosphorus is surrounded by four oxygens, use eight electrons to show four chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 32 valence electrons. And in the above structure, we have already used eight valence electrons. Hence, twenty-four valence electrons are remaining.

Two valence electrons represent one lone pair. So twenty-four valence electrons = twelve lone pairs.

Note that phosphorus is period 3 element, so it can keep more than 8 electrons in its last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are oxygens, so each oxygen will get three lone pairs. And the central atom (phosphorus) will not get any lone pair, because all twelve lone pairs are used.

So the Lewis structure of PO₄^3- looks something like this:

In the above structure, you can see that the octet is completed on the central atom (phosphorus), and also on the outside atoms. Therefore, the octet rule is satisfied.

Now calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of ClO₂^– (5 steps)

#4 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For phosphorus atom

Valence electrons = 5
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 5 – 0 – ½ (8) = +1

• For each oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of PO₄^3- looks something like this:

In the above structure, you can see that the formal charges of atoms are not closer to zero. Therefore, convert lone pair and calculate formal charge again.

Also read: How to draw Lewis structure of H₂O₂ (4 steps)

#5 Convert lone pair and calculate formal charge again

As mentioned earlier, phosphorus is a period 3 element, so it can keep more than 8 electrons in its last shell.

So convert one lone pair from one oxygen atom to make a new bond with the phosphorus atom. And then, the Lewis structure of PO₄^3- looks something like this:

Now one last thing we need to do is, calculate the formal charge again and check the stability of the above structure.

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For phosphorus atom

Valence electrons = 5
Nonbonding electrons = 0
Bonding electrons = 10

Formal charge = 5 – 0 – ½ (10) = 0

• For left oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

• For right oxygen, top oxygen, and bottom oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of PO₄^3- looks something like this:

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of PO₄^3-.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now PO₄^3- is an ion having a negative (-3) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of PO₄^3- looks something like this:

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Related

• Lewis structure of HCl
• Lewis structure of ClO₂^–
• Lewis structure of H₂O₂
• Lewis structure of ClO₃^–
• Lewis structure of CH₂Cl₂

External links

• PO43- Lewis Structure (Phosphate ion) – Chemistry School
• Drawing the Lewis Structure for PO43 – The University of Maryland
• PO43- lewis structure, molecular geometry, hybridization, and bond angle – Topblogtenz
• PO43- Lewis Structure, Hybridization, Polarity, and Molecular Geometry – Techiescientist
• How many lone pairs of electrons are represented in the Lewis structure of a phosphate ion (po43-)? – Quora
• PO43- Lewis Structure in 5 Steps (With Images) – Pediabay
• Chemical Bonding: PO43- Lewis Structure – The Geoexchange
• For PO43 -, phosphate ion, draw the Lewis structure (by counting valence electrons of each atom) – Studocu
• Which of the following phosphate, PO43- Lewis structures is the best, most valid resonance structure? – Pearson
• What is the formal charge on phosphorus in a Lewis structure for the phosphate ion (PO43-) that satisfies the octet rule? – Homework.Study.com
• PO34- Lewis Structure, Properties and more – Geometry of Molecules
• Draw a Lewis structure for PO43- in which the central P atom obeys the octet rule – Chegg
• Lewis structure of phosphate ion – AceOrganicChem
• How many lone pairs of electrons are represented in the Lewis structure of a phosphate ion (PO43-)? – Brainly