POCl3 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair and Detailed Facts


Phosphoryl oxychloride is the full form of POCl3 formula and also commonly known as phosphoryl chloride.

Phosphoryl oxychloride contains chlorine, phosphorus and oxygen atoms in its structure. It is a colourless liquid solution. It has pungent odous. It is quite toxic to inhale for humans. IUPAC name of phosphoryl chloride is phosphoryl trichloride. Lets discuss the POCl3 lewis structure in detail.

How to draw lewis structure for POCl3?

Chemical formula for Phosphoryl oxychloride is POCl3.

POCl3 Molecular weight is 153.33 g mol-1.

POCl3 have Molecular geometry is tetrahedral.

Hybridization of POCl3 is sp3.

POCl3 have polar nature.

Phosphoryl oxychloride (POCl3) molecule is composed of mainly three elements i.e. One phosphorous (P), one oxygen (O) and three chlorine (Cl3) atoms in its structure. POCl3 lewis structure consists of 3 single bonds joined to 3 chlorine atoms and a double bond with 1 oxygen atom surrounds the central phosphorous atom. There are 2 lone electron pair present on oxygen atom and three lone electrons pair present on chlorine atoms.

First is to calculate the total valence electrons existing on POCl3 molecule to outline POCl3 lewis structure. Now, calculate the valence electrons on every atom present in POCl3 structure i.e. valence electrons present on one oxygen atom, one phosphorous and three chlorine atoms present inPOCl3 molecule.

To count the valence electrons of any element just check its position in the groups of periodic table. As the phosphorous atom is present on fifteenth group of periodic table, oxygen atom is on sixteenth group of the periodic table and chlorine atom is on seventeenth group of periodic table.

Therefore, 5 valence electrons on P atom, 6 valence electrons on O atom and 7 valence electrons on three Cl atoms.

Hence, Total valence electrons on phosphorous = 5×1 (P) = 5

             Total valence electrons on oxygen = 6×1 (O) = 6

              Total valence electrons on chlorine = 7×3 (Cl3) = 21

So, total valence electrons for POCl3 lewis structure = 5 (P) + 6 (O) + 7×3 (Cl3) = 32

Now second is to select the element having lowest electronegativity of the POCl3 molecule and place the elements with lowest electronegativity at the central position while drawing POCl3 lewis structure. Because they can more freely share their electrons with neighbouring surrounding atoms or elements.

In this POCl3 molecule, phosphorous atom has 2.19 electronegativity, oxygen atom has 3.44 electronegativity and chlorine atom has 3.16 electronegativity.

From all the three elements phosphorous atom has lowest electronegativity and therefore it goes to the central position in the POCl3 lewis structure and remaining one oxygen and three chlorine gets surrounded to central phosphorous atom.

POCl3 lewis structure showing valence electrons and phosphorous atom is at central position

Third point is to join all the elements or atoms with each other by bonding in the POCl3 lewis structure. In POCl3 we can do two types of bonding with the different distribution of lone electron pairs on oxygen atom. There is always single bond pair with phosphorous and chlorine in both the following POCl3 lewis structures.

Therefore, we have to draw three single covalent bonds with three chlorine atoms. But we can draw either single bond or double with phosphorous atom and oxygen atom in POCl3 lewis structure. So, we have to draw either single covalent bond or double bond with phosphorous and oxygen.

Single covalent bond can draw if we put three lone electron pairs on oxygen and double bonds can draw if we put two lone electron pair on oxygen. Means the formal charge on oxygen get decrease when the double bond is drawn.

POCl3 lewis structure showing two types of bonding and sharing of electrons

Now we have to calculate the presence of valence electrons on POCl3 lewis structure. There are two electrons present in each P-Cl and P-O single covalent bonds. But there is the shifting of one lone pair of electron to form double bond having four bonding electrons in one P=O double bond.

So, there are total 32 valence electrons in POCl3 lewis structure and we have to find total electron pairs. Just divide this value by 2 we have.

Total electron pairs of POCl3 = total valence electrons / 2

Total electron pair of POCl3 = 32/2 = 16

So, we have total sixteen electron pairs on POCl3 lewis structure.

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POCl3 lewis structure octet rule

In POCl3, chlorine atom wants just one valence electron to complete its octet. So it can share one valence electron with phosphorous atom. Therefore, forms three single bonds between phosphorous atom and chlorine atom.

After formation of three P-Cl bonds with chlorine, phosphorous atom has remaining two more unshared valence electrons as it has already shared three electrons with chlorine atom out of its total five electrons. Also the oxygen atom required two additional valence electrons to complete its octet.

So, phosphorous shared three electrons with chlorine out of its five electrons now there are eight valence electrons phosphorous atom has in its outer shell. But as phosphorous atom belongs to the 15th group of the periodic table, it can easily share all of its five valence electrons with other elements to form a stable structure.

In this POCl3 molecule, phosphorous will easily donate its remaining electrons with oxygen atom by making double bonds. So, there are P=O double bonds formed between oxygen and phosphorous atoms, so all elements now completed its octet. Hence, middle P atom formed 3 single covalent bonds linked to 3 chlorine atoms and 1 double bond linked with one oxygen atom.

POCl3 lewis structure formal charges

If the atoms in any lewis structure have low formal charges then the lewis structure diagram is more stable. The formula to calculate any atoms formal charge in lewis diagram is as follows:

Formal charge = (valence electrons – lone pair of electrons – ½ bonding electrons)

First calculate the formal charges on all three chlorine atoms of POCl3 lewis structure. All three chlorine atoms have same lone pair and bond pair electrons, so we can calculate the formal charge for one chlorine atom also.

Chlorine atom: Valence electrons on chlorine = 07

                       Lone pair electrons on chlorine = 06

                       Bonding electrons with chlorine = 2 (one single bond)

Formal charge on chlorine = (7 – 6 – 2/2) = 0

So, all the three chlorine atoms have zero formal charges.

Phosphorous atom: Valence electron on central phosphorous atom = 05

                                   Lone pair electrons on central phosphorous atom = 00

                                       Bonding electrons around central phosphorous atom = 8 (single 3 bonds with Cl)

Formal charge on phosphorous = (05 – 0 – 8/2) = +1

Hence, the central phosphorous atom of POCl3 lewis structure has +1 formal charge.

Oxygen atom: Valence electrons on oxygen = 06

                         Lone pair electrons on oxygen = 06

                         Bonding electrons with oxygen = 2 (one double bond)

Formal charge on oxygen = (6 – 6 – 2/2) = -1

So, the oxygen atom has -1 formal charge.

Thus, the POCl3 has +1 charge on phosphorous atom and -1 charge on oxygen atom but no charge on chlorine atoms, this kind of lewis structure containing bonds are not stable in nature, we have to decrease the charge of oxygen by converting lone electron pair to bond pair as shown in following image.

POCl3 lewis structure showing formal charges

POCl3 lewis structure lone pairs

There are total 16 lone electron pairs in POCl3 lewis structure. POCl3 lewis structure has four bonds joined with one oxygen and 3 chlorine atoms. Now we should only mark the 12 remaining electron pairs as lone pair of electrons on POCl3 lewis structure.

As we already know that chlorine and phosphorous atoms belongs to 3rd period of periodic table and they can possess more than eight electrons in its outer valence shell. Likewise oxygen belongs to the 2nd period of the periodic table and it does not have more the eight electrons in its last outer shell.

Let us start to mark lone pair electrons from outer atoms i.e. the one oxygen atom and three chlorine atoms. Therefore, oxygen and three chlorine atoms have three lone electron pairs and phosphorous have no lone electron pair as all the 12 electron pairs already get shared between O and Cl.

POCl3 lewis structure shape

In POCl3 lewis structure, the central phosphorous atom has 4 bonds with 4 atoms i.e.1 oxygen and 3 chlorine atoms. All the atoms get arranged in that possible position with each other so that they can reduce the repulsive forces between electron bond pairs.

The VSEPR theory tells that, any molecule can adopts the geometry to decrease the repulsion forces i.e. in any lewis structure bond pair electrons of any atom has no repulsion if there are lone pair electrons are not present. The generic formula for POCl3 molecule is AX4.

The shape of POCl3 lewis structure has tetrahedral shape according to its molecular geometry as the central phosphorus atom gets attached with four other atoms.

POCl3 Hybridization

Steric number is a base to find the hybridization of any structure or molecule. POCl3 lewis structure hybridization can be assigned by its central phosphorous atoms steric number.

Steric number is the sum of total number of bonded atoms linked (attached) with central atom and lone pair of electrons present on it.

Steric number of POCl3 = (no. of bonded elements or atoms attached with phosphorous + phosphorous atom lone pair of electrons)

As we see the POCl3 lewis structure above, central phosphorous atom joined with one oxygen atom and three chlorine atoms i.e. four bonds with four atoms and have no lone electron pairs on it.

So, POCl3 steric number = 4 + 0 = 4

POCl3 lewis structure has a four steric number after calculation, so it is in sp3 hybridization of phosphorous in POCl3 structure.

POCl3 lewis structure resonance

Resonance structure shows the variation in electron distribution from one structure to another structure. There are some rules to draw the resonance structure for any chemical compound or molecule or for lewis structure.

The molecule of structure needed multiple bonds (double/ triple bond) and at least one lone electron pair should be on adjacent atom in the structure. If any structure have fulfilled this conditions, so we can easily draw resonance structure of any molecule with distribution of electrons and charges on atoms in the molecule.

Resonance structure of POCl3 molecule is not possible as it is not a stable structure to form resonance. As the phosphorous atom have double bonds with oxygen and three single bonds with each chlorine atoms. So, phosphorous has an extended octet.

POCl3 lewis structure showing stable POCl3 molecule by reducing the charge on oxygen

POCl3 polar or nonpolar

POCl3 molecule is a polar molecule as it has an unequal distribution of electrons throughout it structure. POCl3 molecule consists of covalent bonds i.e. the phosphorous oxygen (P-O) bond is faintly-moderately covalent in nature and the phosphorous chlorine (P-Cl) bonds are moderately covalent in nature.

Polarity of POCl3 molecule can be determined by drawing a symmetry lines through the POCl3 structure. The molecule is polar if one or few lines are on symmetry in the structure. Even the molecule is polar if no symmetry lines drawn through the structure. So POCl3 molecule lacks the symmetry line in its structure.

If the POCl3 molecules bonds of an atom is either covalent or ionic in nature can be determined by the electronegativity difference of phosphorous and oxygen and phosphorous and chlorine atoms. If the result value is from 0 to 1.6 then it is a covalent bond, if the value is from 1.8 to 3.0 then it is ionic bond and if the value of bond is 1.7 exactly then it has neutral bond.

For POCl3 molecule, 3.5 is the electronegativity of oxygen and 2.19 is the electronegativity of phosphorous. So, the electronegativity difference between phosphorous and oxygen atom is 1.3 which shows bond is slightly-moderately covalent.

Also 3.2 is the electronegativity of chlorine and 2.19 is the electronegativity of phosphorous and its difference is 1.0 which makes the bond moderately covalent. So, POCl3 lewis structure is comes under polar molecules.

POCl3 lewis structure bond angle

When we determine the molecular geometry of POCl3 molecule with the help of AXN table, it shows the phosphorous has no lone electron pair and forms four bonds with four atoms i.e. O and three Cl, which is similar to AX4. Here, A = central atom and X = number of bonds formed with central atom.

As POCl3 lewis structure has tetrahedral shape so it has 109.8 degree bond angle although it may be quite differ because of double bond in its molecule.

POCl3 lewis structure
POCl3 lewsi structure showing bond angle 109.8 degree

POCl3 Uses

  • Phosphoryl oxychloride is the precursor to N, N-dimethyl phosphoramidic dichloride.
  • By multistage chemical synthesis phosphoryl trichloride gets transformed to nerve gases. It is an initiator to chemical weapons.
  • Phosphorus oxychloride is broadly used in the manufacturing of alkyl and aryl orthophosphate triesters.
  • In cryoscopy POCl3 is used as a solvent.
  • POCl3 also used in agricultural chemicals (non-pesticidal), flame retardants, intermediates, processing aids, etc.
  • POCl3 is used in laboratories for various dehydration reactions.
  • In semiconductor industries POCl3 is also used as a source of liquid phosphorus in diffusion procedures.
  • POCl3 also plays a vital role in the preparation of Vilsmeier’s reagent as it is used in Vilsmeier-Haack reaction.

Dr. Shruti Ramteke

Hello everyone I am Dr. Shruti M Ramteke, i did my Ph.D in chemistry. I have five years of teaching experience for 11-12 standard, B,Sc and MSc in chemistry subject. I have published total five research articles during Ph.D on my research work and i have fellowship from UGC for my Ph.D. My Masters with specilization Inorganic chemistry and my graduation with chemistry, zoology and environmental science subjects. thank You

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