PCl3 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair, And Detailed Facts


In this article, we should discuss bout the PCl3 lewis structure and much more facts. Let’s start the article with important facts about PCl3.

In the PCl3 lewis structure. The oxidation state of central P is +3. So, here P makes only three bonds where two electrons reside as lone pair. The central P is sp3 hybridized and the lone pair is situated in one of the hybrid orbitals. So, that lone pair can be donated easily and it can behave as a lewis base. But the lewis acidity decreases due to three electronegative Cl atoms being attached.

It can accept electrons in its vacant d orbital and also behave as lewis acid. the bond angle of the PCl3 lewis structure is less than 1090, due to avoiding repulsion between lone pairs of P and Cl atoms. In organometallic chemistry, PCl3 is used as a π acidic ligand and can stabilize the lower oxidation state of metal.

Some details facts about PCl3

PCl3 in its physical state is a fuming liquid having colorless to yellowish sometimes. The smell of phosphorus trichloride is unpleasant like hydrochloric acid. the molar mass of the PCl3 is 137.33 g/mol. The density of the molecule is 1.574 g/cm3. The melting point and boiling point of PCl3 are 179.6 K and 349.2 K respectively.

The industry method for the preparation of PCl3 is a reaction with chlorine gas with white phosphorus. PCl3 is used as solvent here and removed PCl3 to avoid the formation of PCl5.

P4 + 6 Cl2 → 4 PCl3

In 31P NMR the molecule exhibits a singlet signal around +220 ppm with the reference of H3PO4.

PCl3 can behave as both oxidizing as well as a reducing agent. It can acts as an electrophile due to a deficiency of electrons in the P center.

3 PhOH + PCl3 → P(OPh)3 + 3 HCl

PCl3 + 3 EtOH + 3 R3N → P(OEt)3 + 3 R3NH+Cl

It can react with the Grignard reagent to give the phosphorus ylide.

3 PhMgBr + PCl3 → Ph3P + 3 MgBrCl

PCl3 also acts as a nucleophile in many organic reactions.

PCl3 + RCl + AlCl3 → RPCl+3 + AlCl4

How to draw the lewis structure for PCl3?

To draw the PCl3 lewis structure, we need to follow the octet rule, a s P is the p block element it should follow the octet rule. After drawing the PCl3 lewis structure, then we can calculate the bond pairs, lone pairs, and other covalent properties of the PCl3 lewis structure.

PCl3 lewis structure
PCl3 Lewis Structure

Step 1 – In the First step of the PCl3 lewis structure, we should calculate the valence electrons for the PCl3 molecule and add them together. There are two types of atoms P and Cl present. So, we individually calculate the valence electrons for P as well as Cl. P is the group 15th VA element. It belongs to the N family, so it has five electrons in its valence shell.

Again, Cl is group17th VIIA element and belongs to the F family. Cl is a halogen and from the electronic configuration, we can say that it has seven electrons in its valence shell. There are three Cl atoms are present so the total valence electrons for the PCl3 lewis structure is, 5+(7*3) =26 electrons.

Step 2 – Now in the 2nd step we select the central atom for the PCl3 lewis structure. P is less electronegative according to the lewis structure formula P is the central atom here. Three Cl atoms are present at the surrounding positions of P atoms.

Step 3 – Now we should check the octet rule here. Both P and Cl are p block elements. So, they should follow the octet rule. According to the octet rule p block element should complete their valence orbital by eight electrons as the p orbital can accumulate a maximum of six electrons and the s orbital contains a maximum of two electrons. So, the electrons needed for a complete octet in the PCl3 lewis structure is 4*8  = 32 electrons. But the available valence electrons for the PCl3 lewis structure is 26 electrons.

So, the electrons required 32-26 = 6 electrons. Those 6 electrons will accumulate by the 6/2 = 3 bonds. So, in the PCl3 lewis structure, there will be minimum of 3 bonds are required.

Step 4 – Now we connect all the atoms in the PCl3 lewis structure via the required number of bonds. We connect three Cl atoms with a central P atom with three sigma bonds to complete their octet in the PCl3 lewis structure.

Step 5 – in the last step, we check whether all the atoms in the PCl3 lewis structure are satisfied with their octet or not. After the successive single bond formation if there is necessary that the octet is not complete then we add multiple bonds between atoms. Sometimes we add the lone pairs which are present in the valence electrons but do not participate in the bond formation. P has Five electrons in the valence shell and only formed three bonds with three electrons, so the rest of the two electrons are present as lone pair over the P atom.

Cl has seven electrons in its valence shell but formed only one bond with the P atom and the rest of the six electrons are present as three pairs of lone pairs over Cl atoms.

PCl3 lewis structure shape

The shape of the PCl3 lewis structure depends on the valence electrons count by VSEPR theory, or based on hybridization, the shape is determined. The number of bond pairs and lone pairs also influence the shape of a molecule. The shape of the PCl3 lewis structure around central P is trigonal pyramidal with one pair of lone pairs.

PCl3 Shape

The total electron count for the PCl3 lewis structure is 5+3 = 8. According to VSEPR (Valence Shell Electrons Pair Repulsion) theory, if the electron count for any AX3 type molecule will be eight and the central atom contains one lone pair then the shape becomes trigonal pyramidal instead of tetrahedral. The geometry of the molecule is tetrahedral but the shape of the molecule is trigonal pyramidal as lone pair does not consider in the shape of the molecule.

So, the shape of the PCl3 lewis structure is trigonal pyramidal, actually, due to avoiding the repulsion of the lone pairs, the molecule adopts this kind of shape along with the bond angle.

PCl3 lewis structure lone pairs

The lone pairs of the PCl3 lewis structure are the total lone pairs over the four atoms. P and Cl both contain different numbers of lone pairs, so we individually calculate the lone pairs and added them, together to get the number of lone pairs for the PCl3 lewis structure.

PCl3 Lone Pairs

In the PCl3 lewis structure, the central P atom has five electrons in its valence shell. That means it can use those five electrons in the bond formation. But there are only three sigma bonds present between P and three Cl atoms in the PCl3 lewis structure. So, P makes three bond pairs via sharing electrons with three Cl atoms. Now rest of the two electrons which are present in the valence shell do not participate in the bond formation. Those electrons contribute to the octet rule. Those two electrons exist as lone pair over the P atom.

Now for other three surrounding Cl atoms has seven electrons each for the valence shell. But in the PCl3 lewis structure, one Cl makes only one bond with the P atom via sharing only one electron from its outermost orbital. So, the remaining six electrons which are not involved in the bond formation but involved in the octet completion exist as three pairs of lone pairs over every Cl atom.

So, in the PCl3 lewis structure, the total number of lobe pairs available is 2+(3*2) = 8 pairs of lone pairs.

PCl3 lewis structure formal charges

The PCl3 lewis structure is neutral but if there is any charge that appears on the individual atom that should be calculated via formal charge. The formal charge is a hypothetical concept where we assume the same electronegativity for P and Cl atoms in the PCl3 lewis structure.

The formula we can use to calculate the formal charge for the PCl3 lewis structure is, F.C. = Nv – Nl.p. -1/2 Nb.p.

Where Nv is the number of electrons in the valence shell or outermost orbital, Nl.p is the number of electrons in the lone pair, and Nb.p  is the total number of electrons that are involved in the bond formation only.

As the environment and bonding nature of P and Cl are different so we calculate the individually formal charges for P and Cl atoms.

The formal charge of P is, 5-2-(6/2) = 0

The formal charge of Cl is, 7-6-(2/2) = 0

From the calculation of the formal charge of PCl3 lewis structure, we can say that there is no charge is appear for individual atoms and the molecule is neutral.

PCl3 lewis structure octet rule

In the PCL3 lewis structure, P and Cl both are p block elements so they have to follow the octet rule. According to the octet rule for the p block element, every atom should complete its valence shell by eight electrons.

PCl3 Octet

The electronic configuration of P is [Ne]3s23p3. P is group 15th VA element. The 3s and 3p orbital P contains five electrons and required three more electrons in the 3p orbital to complete the octet. So, P makes three bonds with three unpaired electrons from the 3p shell and shares one electron from three Cl atoms, this way the 3p shell of P is completed via six electrons and two electrons already exist in the 3s shell as lone pair. So, P completes its octet by making three bonds.

Now Cl is group 17th VIIA element. The electronic configuration is [Ne]3s23p5. So, it has seven electrons in its valence 3s and 3p shells. So, Cl needs one more electron in its 3p orbital to complete its octet. Now each Cl atom makes a sigma bond with p via sharing one electron and completing its 4p orbital by six electrons. Now, Cl has eight electrons among two involved in the bond pair and the rest of six involved in the lone pair.

So, in the PCl3 lewis structure, both P and Cl complete their octet.

PCl3 lewis structure resonance

In the PCl3 lewis structure, electron delocalization occurs between the different skeletons of PCL3 via resonance. The electronic cloud over P is distributed and delocalized because the lone pair is present in one of the hybrid orbitals.

PCl3 Resonating Structures

All three structures are the different resonating structures of the PCl3 lewis structure. Structure II is the most contributing structure in all the resonating structures. Because structure II is the most stable, as there are more covalent bonds present and the negative charge is present over the electronegative Cl atom and the positive charge is over the electropositive P atom. Structure III is a less contributing or least stable structure because the positive charge is on electronegative Cl atoms, which is a destabilizing factor.

PCl3 hybridization

In the PCl3 lewis structure, P is electropositive and Cl is electronegative so their orbital energy is different and under the normal condition, they cannot form a bond. So, they undergo hybridization to form an equal number of hybrid orbitals to an equal number of atomic orbitals are mixed. These hybrid orbitals are of equivalent energy. In the PCl3 lewis structure, central P undergoes sp3 hybridization by mixing one s and three p atomic orbitals.

We used the formula to predict the hybridization of the PCl3 lewis structure is,

H = 0.5(V+M-C+A), where H= hybridization value, V is the number of valence electrons in the central atom, M = monovalent atoms surrounded, C=no. of cation, A=no. of the anion.

The valence electrons for P in the PCl3 lewis structure is 5 and there are three surrounding Cl atoms present.

So, the mode of hybridization of central P in the PCl3 lewis structure is, 5+3 = 8(sp3)

Structure       Hybridization value  State of hybridization of central atom    Bond angle
Linear        2sp /sd / pd         1800
Planner trigonal    3sp2          1200
Tetrahedral         4sd3/ sp3        109.50
Trigonal bipyramidal5 sp3d/dsp3          900 (axial), 1200(equatorial)
Octahedral       6sp3d2/ d2sp3       900
Pentagonal bipyramidal7sp3d3/d3sp3         900,720

              

So, from the hybridization table it is evident that, if the number of orbitals involved in hybridization is equal to 4 then the central atom should be sp3 hybridized.

Let’s understand the hybridization of the PCl3 lewis structure in detail.

PCl3 Hybridization

From the box diagram of the PCl3 lewis structure, it is evident that the lone pair over P is also involved in the hybridization and it is situated in one of the hybrid orbitals. So, the lone pair easily be donated and increase the lewis basicity for PCl3.

Three Cl atoms contribute one electron to P and they formed a bond via sp3 hybridization.

PCl3 polar or nonpolar

From the PCL3 lewis structure shape, we can say it is an asymmetric molecule and there is a huge electronegativity difference between P and Cl atoms. So PCl3 is a polar molecule.

The electronic dipole flow occurs from electropositive P to electronegative Cl atoms. Due to the asymmetric shape of the molecule, there is resultant dipole moment is present in the PCl3 lewis structure. Which made the molecule polar.

PCl3 uses

It can be used as,

  • Gasoline additive
  • Textile finishing
  • Making pesticides
  • Organometallic ligands
  • Lewis base
  • The oxidizing and reducing agent

Conclusion

PCl3 is a lewis base and can acts as a nucleophile also. It can be used as a catalyst in many organic reactions. Due to avoiding the repulsion of the lone pairs the bond angle of Cl-P-Cl is less than 1090.

Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.

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