Lewis structure of POF3

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The Lewis structure of POF₃ contains one double bond and three single bonds, with phosphorus in the center, and oxygen and three fluorines on either side. There are three lone pairs on each fluorine atom, two lone pairs on the oxygen atom, and the phosphorus atom does not have any lone pair.

Contents

Steps

By using the following steps, you can easily draw the Lewis structure of POF₃.

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

Now POF₃ has one phosphorus atom, one oxygen atom, and three fluorine atoms.

So the total number of valence electrons = valence electrons of phosphorus atom + valence electrons of oxygen atom + (valence electrons of fluorine 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 fluorine as follows:

Electronegativity value of phosphorus = 2.19
Electronegativity value of oxygen = 3.44
Electronegativity value of fluorine = 3.98

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

So now, put phosphorus in the center and oxygen and three fluorines on either side. And draw the rough skeleton structure for the Lewis structure of POF₃ something like this:

Skeleton structure for Lewis structure of POF₃ | Image: Root Memory

Also read: How to draw Lewis structure of H₃PO₃ (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 fluorines, use eight electrons to show four chemical bonds as follows:

Four chemical bonds shown between atoms | Image: Root Memory

#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 a period 3 element, so it can keep more than 8 electrons in its last shell. And both (oxygen and fluorine) are the period 2 elements, so they can not keep more than 8 electrons in their 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 fluorines, so oxygen and three fluorines 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 POF₃ looks something like this:

Lone pairs marked on Lewis structure of POF₃ | Image: Root Memory

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 CF₃Cl (4 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 fluorine 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 POF₃ looks something like this:

Formal charges are not closer to zero | Image: Root Memory

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 XeCl₃^– (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 the oxygen atom to make a new bond with the phosphorus atom. And then, the Lewis structure of POF₃ looks something like this:

Lone pair of oxygen is converted, and octet is completed on atoms | Image: Root Memory

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 fluorine 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 POF₃ looks something like this:

Formal charges are calculated, and got the stable Lewis structure of POF₃ | Image: Root Memory

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of POF₃.

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

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Deep

Rootmemory.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.