Lewis structure of POCl3

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The Lewis structure of POCl₃ contains one double bond and three single bonds, with phosphorus in the center, and oxygen and three chlorines on either side. There are three lone pairs on each chlorine atom, two lone pairs on the oxygen atom, and the phosphorus atom does not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of POCl₃.

#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, oxygen is a group 16 element, and chlorine is a group 17 element. Hence, phosphorus has five valence electrons, oxygen has six valence electrons, and chlorine has seven valence electrons.

Now POCl₃ has one phosphorus atom, one oxygen atom, and three chlorine atoms.

So the total number of valence electrons = valence electrons of phosphorus atom + valence electrons of oxygen atom + (valence electrons of chlorine atom × 3)

Therefore, the total number of valence electrons = 5 + 6 + 21 = 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, oxygen, and chlorine as follows:

Electronegativity value of phosphorus = 2.19
Electronegativity value of oxygen = 3.44
Electronegativity value of chlorine = 3.16

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

So now, put phosphorus in the center and oxygen and three chlorines on either side. And draw the rough skeleton structure for the Lewis structure of POCl₃ something like this:

Also read: How to draw Lewis structure of SOCl₂ (5 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since phosphorus is surrounded by oxygen and three chlorines, 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 both (phosphorus and chlorine) are the period 3 elements, so they can keep more than 8 electrons in their 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 oxygen and three chlorines, so oxygen and three chlorines 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 POCl₃ 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 ICl (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 oxygen atom

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

Formal charge = 6 – 6 – ½ (2) = -1

• For each chlorine atom

Valence electrons = 7
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 7 – 6 – ½ (2) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of POCl₃ 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 SO₂Cl₂ (5 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 the oxygen atom to make a new bond with the phosphorus atom. And then, the Lewis structure of POCl₃ 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 oxygen atom

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

Formal charge = 6 – 4 – ½ (4) = 0

• For each chlorine atom

Valence electrons = 7
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 7 – 6 – ½ (2) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of POCl₃ looks something like this:

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of POCl₃.

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

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Related

• Lewis structure of SOCl₂
• Lewis structure of ICl
• Lewis structure of SO₂Cl₂
• Lewis structure of C₄H₁₀
• ClO₂ Lewis structure

External links

• Chemical Bonding: POCl3 Lewis Structure – The Geoexchange
• POCl3 Lewis Structure in 6 Steps (With Images) – Pediabay
• POCl3 lewis structure, molecular geometry, hybridization, bond angle – Topblogtenz
• Phosphoryl Chloride, POCl3 Molecular Geometry & Polarity – Tutor-Homework.com
• Phosphorus oxychloride (POCl3) Lewis structure – Chemistry School
• Phosphorous Oxychloride (POCl 3 ) Formal Charge – Chemistry Learner
• POCl3 Lewis Structure, Molecular Geometry, Hybridization, Bond Angle and shape – Geometry of Molecules
• Lewis Structure of POCL3? – Laurence Lavelle
• Draw the Lewis Dot Structure for POCl3 – Pearson
• POCl3 Lewis Structure (Phosphoryl Chloride) – Pinterest
• Phosphoryl chloride, POCl3, has the skeleton structure – Chegg
• POCl3 Geometry and Hybridization – Chemistry Steps
• What is the Lewis structure for POCl3? – OneClass
• Phosphoryl chloride, POCl3, has the skeleton structure – Numerade
• Phosphorus oxychloride has the chemical formula POCl3, with P as the central atom – Brainly
• Confused about POCl3 structure – Reddit
• Draw a Lewis structure of POCl3 – Quizlet
• Draw Lewis structure for POCl3 – Course Hero