PCl5 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair And Detailed Facts

Here,  we will explore how to draw pcl5 lewis structure, hybridization, formal charges,  chemical nature, polarity parameters, and other related properties of PCL5, along with its uses.

Phosphorous belongs to the 15th group of the periodic table, i.e., the Nitrogen family having outermost electrons in the 3p subshell. In PCl5, Phosphorous is bonded to 5 atoms of chlorine via five single bonds and found in yellow-greenish crystalline solid form with a molecular weight of 208.2g/mol and emit a very unpleasant odor. Also, Pcl5 lewis structure exhibited extended octet rule.

Steps for drawing PCl5 lewis structure

Let’s draw the lewis dots for PCl5 by following the below steps one by one:

Find how many number of valence electrons are available for bonding in PCL5

P (Z = 15) =  [Ne] 3s²3p³  ie. 5 valence electrons are there for Phosphorous

Cl (Z = 17) = [Ne] 3s²3p⁵ ie. 7 electrons for each chlorine atom

Total count of electrons = 5 + 7*5 ( as total Cl =5 ) = 40

  • As the less electronegative atom will occupy the central position, hence P placed at centre and Cl atoms place at outer sides.
  • Generally every atom first a sigma donor ie we will  assign shared pairs of electrons firstly for single bonds and rest of the electrons taken as a lone pair. 
  • One should noted that arrangement of the electrons pairs in the lewis structure is such that it indicates a stable configuration. Now, following the procedure above,  we get a picture of lewis dots of PCL5.
PCL5 Lewis structure
PCl5 lewis structure  (Figure 1)

PCl5 lewis structure octet rule

According to the octet rule, after the bond formation between the respective atoms (like here we have Cl and P), all the atoms in the lewis formula should have a total of 8 electrons. However, in the PCL5,molecule, there are 10 electrons available for P and 8 electrons for the Cl atom.

It happened due to the presence of d orbitals, due to which they can have an expanded octet. Such molecules are called hypervalent compounds. 

Apart from PCL5, other molecules like IF7 and SF6 also come under this category; these molecules do follow the octet rule. In other words, have an expanded octet.

PCl5 lewis structure resonance

PCL5 is ionic in nature and capable of showing resonating hybrid structure as given below and again these structure satisfied the expanded octet rule as P contains 10 electrons as explained in the octet rule.

Hybrid PCl5 resonating structures  (Figure 2)

Calculation of formal charges for PCL5 lewis structure

Formal charges =  [valence electrons – unbonded electrons – ½ bonded electrons]

Calculation of formal charge for Phosphorous atom

Valence electrons = 5 ( as belong to second group)

Unbonded electron count = 0

Bonded electrons = 10

F.C =  5 – 0 –  10/2 =  0

Calculation of formal charge for chlorine atom

Total valence count = 7

Unbonded electron count = 6

Bonded electrons = 2

F.C = 7 -6 – 2/2 =  0

Hence total formal charge = 0

Hybridization of PCl5

Hybridization means the overlapping of atomic orbitals of the intended atoms such that they redistribute their energies resulting in the formation of new orbitals called hybridized orbitals. The whole phenomenon is called hybridization. The reported hybridization for PCl5 is Sp3d, in which one orbital, three p orbitals, and one d orbitals are involved. Let’s see how it is happening.

 Steps involves in hybridization of PCL5:

steps hybridization
Figure 3. Hybridization steps showing formation of PCL5

PCL5 structure lone pairs

As hybridization has been explained above, here a question arises does PCL5 has any lone pairs? Usually, lone pair means those which do not participate in the bonding. However, it is clear from the hybridization steps that every electron is involved in overlapping. Therefore, total lone pair count is zero for  phosphorous pentachloride.

PCL5 lewis structure bond angle, shape and type

PCL5 adopted trigonal bipyramidal geometry in which all the bond angles are not equivalent ie.  All the chlorine atoms attached to the central atom are not in same environment. Out of 5 , 3 cl atoms are in same plane while remaining two in different one, all together forming a trigonal bipyramidal arrangement as shown in the above picture.

Trigonal bipyramidal shape (wikipedia)

Types of bonds are present in PCL5

As discussed above, all the cl atoms are not same and possessed different bond angels as well as bond type.

Out of 5 covalent bonds, three bonds lying in the trigonal plane and known as equatorial bonds while remaining two, one lie above the plane ( represented by dash bond in fig 1) and the other one below the plane ( represented by dash bond) and named as axial bonds.

In general, bond angle is defined as angle between two orbitals which containing bonding electrons around the central atom in the given molecule. There are two bond angles as  two type of bonds exists in the structure. As it can be observed from the given picture, the angels between two equatorial chlorine atom is 120o whereas the angle between a equatorial and axial chlorine atom is 900

Here a = axial bond, b= equatorial bond (Figure 5)

PCL5 polar or nonpolar ?

The polar nature of PCL5 is quite surprising as due to the presence of two types of bonds, it is expected that it must be polar in nature. However, the geometry, i.e., trigonal bipyramidal, is accountable for the arrangement in such a way that bonds opposite cut down the dipole moments of each other, which results in a non-polar nature.

PCL5 uses

  • It acts as a chlorinating agent as it has comparatively two loose chlorine atoms at axial positions, which can be easily abstracted. It can act as a suitable agent for chlorination.
  • They are used as a dehydrating agent ( removal of water) in many chemical reactions in chemistry.
  • Two popular medicines, penicillin and cephalosporin, are manufactured by using PCL5. It acts as a catalyst in many reactions, such as acetyl cellulose formation and typical cyclization reactions.
  • Use to form acid chlorides.
  • Many organic phosphorous compounds are being prepared by it.

Frequently asked questions

what is the nature of PCL5 ?

Yes, it is because of its reactive nature as when it comes in contact with water it react vigorously and also damage the human skin. Furthermore, inhalation of PCL5  for longer duration can cause irritation in the nasal cavity and throat.

Why are axial bonds longer than equatorial in PCL5?

The axial bonds are longer than the equatorial bonds. It can be explained in terms of repulsive forces between electron pairs due to different bond angles. As shown in figure 4, chlorine atoms at axial positions are being repelled by three equatorial chlorine atoms at an angle of 90o and one at 1800, respectively.

Generally, repulsions between the electron pairs are inversely proportional to the bond angles. Therefore, repulsions between the electron pair at 1800 can be neglected compared to those at 90o. Thus considering only the repulsions between electrons pair at 90o, we can conclude that three electron pairs repel each axial bond.

This indicates that the axial bond pair encounter greater repulsions from other bonds, and therefore, the axial bond is slightly longer than an equatorial bond.

Like PCl5, PI5 can exist ?

The hybridization of PCL5 takes place due to the small size and electronegative nature of the Cl atom, whereas, Iodine is relatively much larger in size and also more electropositive; hence, hybridization is restricted in this case, and formation of PI5 is not possible.

Is PCl5 oxidizing agent or a reducing agent ?

It has an oxidation state of +5 and cannot show beyond. Therefore, PCl5  can not act as a reducing agent as the reducing agent itself undergo oxidation but cause the reduction of other molecules. Hence, there is the only option of reducing agent left for PCL5 as P atom has tendency to reduce its oxidation number from + 5 to +3. 

How is PCl5 stored inside the chemical lab ?

well stoppered bottles are used to keep PCL5 because it is quite reactive and can react with water molecules present in the surrounding environment to give hydrochloric acid as well as orthophosphoric acid.

Why solid PCL5  exist as [PtCl4]+ [PtCl6]?

PCL5 has a trigonal bipyramidal geometry which is not stable due to uneven bond lengths of axial and equatorial bonds. Therefore, this geometry is not regular and PCl5 tend to move towards more stable spatial arrangement of the atoms ( ie more stable geometry). As a result in solid phase, PCl5 dissociates in order to attain more stable tetrahedral and octahedral geometries.

PCl5  is a base or acid ?

According to lewis definition of base and acid; a acid can accept electrons pair from other species while base is a substance which can denote electron pair. Since in PCl5, due to presence of empty d orbitals it can readily accept electrons and hence act as a lewis acid.

What is best way to form PCl5 ?

 PCl5 is formed either using batch or continuous processing in which, PCl3  is taken as precursor and firstly dissolve in carbon tetrachloride and  this mixture is then poured into a jacketed vessel containing stirrer and a fixed refluxed condenser.

The whole apparatus is tightly covered and Cl2 is introduced by means of jacketed vessel. The whole process is carried out in an inert environment due to reactive nature of PCl5. After the reaction the left CS2 is discarded.

Is PCl5  soluble in H2O ?

Since, PCl5 is non- polar in nature, it cannot mixed in a polar solvent like water. However, it can readily dissolve in non-polar solvent.

Which one is more reactive PCL5 or PCl3 ?

In world of chemistry, reactivity of any substance is inversely proportional to  the stability of  the substance ( reactivity = 1/stability). In accordance with this rule, PCl3 relatively has more stable geometry than the PCl5. Hence, less reactive in nature.

Interesting facts !

Phosphorus is the most abundant element of the 15th group even though it places ten positions in abundance amongst all the elements on the earth.

Phosphorous is important because of its occurrence in phosphate rocks which can be used as the source of phosphatic fertilizers and are also capable of forming other useful alloys.

Chlorine is the 3rd abundant element in the ocean and places at 21st rank in the list of most abundant elements 

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