PBr3 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair and Detailed Facts

Phosphorous tribromide is the chemical name of PBr3. It shows a distinctive property of acts both like as a Lewis base and a Lewis acid.

Phosphorous tribormide (PBr3) is a liquid form compound. It has no colour and has a pungent odour. PBr3 resembles to PCl3 and PF3 in its structure and properties. Here, in this editorial we are discussing about detailed features of PBr3 lewis structure, its drawing, hybridization, charges, shape, etc.

How to draw lewis structure for PBr3?

While drawing any lewis structure the below points should be follows:

  1. Calculation of total valence electrons present on structure.
  2. Select the element with lowest electronegativity for central position in structure.
  3. Do bonding between all the elements present in structure.

PBr3 lewis structure consists of two elements i.e. one phosphorous and three bromine atom in its structure. Therefore, first we should have to count valence electrons of both phosphorous and bromine elements.

Formula is: total valence electrons in PBr3 = Phosphorous (P) valence electrons + Bromine (Br) valence electrons

Valence electrons on P are 5 in its outer orbit. Valence electrons of Br are 7 in its outer orbit but we have to multiply it by 3 due to presence of three Br atoms. Now let us count the total valence electrons for PBr3 lewis structure.

PBr3 total valence electrons = 5 (P) + 7×3 (Br3) = 26

Hence, there are total 26 valence electrons in PBr3 lewis structure.

PBr3 Lewis Structure
PBr3 lewis structure showing valence electrons

Next is to choose the lowest electronegativity atom from the molecule or structure. The lowest electronegative atom possesses the central position due to its capacity to easily donate its electrons to other elements. 

Here, in PBr3 phosphorous atom has electronegativity of 2.19 and bromine atom has electronegativity 2.96. So, phosphorous atom is less electronegative than bromine atom and possesses the central position at PBr3 lewis structure.

Now, third is to bonding between all the elements of PBr3 lewis structure. Draw three solo P-Br bonds between one P and all three Br atoms in PBr3 lewis structure.

PBr3 lewis structure showing bonding between all elements

PBr3 lewis structure octet rule

Octet rule means presence of eight electrons in any elements outer shell. To draw the lewis structure of any molecule first thing is to complete the outermost elements octet i.e. the outermost elements of any structure should contain eight elements in its outer orbit. Also, the lewis structure is being more stable if elements of that structure have eight electrons in its outer shell/orbit i.e. complete octet.

So, we have to try to complete the octet of all three bromine atoms. As in PBr3 lewis structure, each bromine atom has need of only single valence electron to fill eight electrons in its outer shell or complete its octet.

As there is already bonding between three bromine atoms and one phosphorous atom i.e. three P-Br single covalent bonds. Two valence electrons get involved in formation of every single covalent bond. So, in three bonds formation total six valence electrons was used.

After using six electrons in bonding there are more 20 valence electrons get remain for distribution on atoms. Now, the all remaining valence electrons get distributed on middle P atom and outer three Br atoms to fill its octet. So we will get the PBr3 lewis structure as follows.

Thus, in the below PBr3 lewis structure there are 6 valence electrons on each Br atom and two valence electrons on one P atom showing complete octet of both the elements.

PBr3 lewis structure showing octet of all elements

PBr3 lewis structure formal charges

If the atoms have little formal charges in any lewis structure then the there is more stability in lewis structure. The calculative formula for formal charge calculation of any atoms in lewis diagram is as follows:

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

First let we calculate the all three bromine atoms formal charges on PBr3 lewis structure. There is equal lone pair and bond pair electrons on all three bromine atoms, so just we have to calculate the lone bromine atom formal charge.

Bromine atom: Valence electrons on bromine = 07

                       Lone pair electrons on bromine = 06

                       Bonding electrons with bromine = 2 (one single bond)

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

Thus, there is zero formal charges on all the three bromine atoms.

Phosphorous atom:Valence electron on central phosphorous atom = 05

                          Lone pair electrons on central phosphorous atom = 02

                          Bonding electrons around central phosphorous atom =06 (single 3 bonds)

Formal charge on phosphorous = (05 – 02 – 6/2) = 0

Hence, the central phosphorous atom of PBr3 lewis structure has zero formal charge.

So, this concludes that PBr3 lewis structure has no formal charges on it.

PBr3 lewis structure lone pairs

As we see the PBr3 lewis structure, the single outer bromine atom contains three lone electron pairs. So, all the three outer bromine atoms have total nine lone electron pairs in PBr3 lewis structure. Similarly, the central phosphorous atom in PBr3 lewis structure contains one lone pair of electron on it.

Thus, the total lone electron pairs present on PBr3 lewis structure is ten i.e. nine on three Br atoms and one on one phosphorous atom.

PBr3 lewis structure shape

According to molecular geometry of PBr3 molecule, the PBr3 lewis structure has a trigonal pyramidal shape. The molecular geometry shows the PBr3 lewis structure contains the phosphorous at middle (central) or apex position and the three oter bromine atoms is situated on the trigonal base corner positions. Tetrahedral geometry and trigonal pyramidal geometry is quite differing from each other.

The PBr3 lewis structure has trigonal pyramidal shape, as the central phosphorous atom has one lone electron pair which prominently cause repulsion with neighbouring bonded bromine atoms. Thus, the three P-Br bonds gets moved downwards also more away from their original position. So, due to these reasons the PBr3 has shape of trigobal pyramid.

Electron geometry of phosphorous tribromide (PBr3) molecule shows tetrahedral geometry, as the central phosphorous atom contains one electron lone pair and it gets bonded with three bromine atoms. So, PBr3 lewis structure has four sections of electron densities i.e. one lone pair (on P) and three bond pair (on 3Br) surrounds the central P atom.

PBr3 lewis structure showing the trigonal pyramidal (tetrahedral) shape

VSEPR theory says, the four sections of electron densities with central phosphorous atom has tetrahedral electron geometry, as there is less repulsion between electron pairs in this position. Also the AX3N1 generic formula applies on PBr3 lewis structure.

So, the final conclusion is PBr3 lewis structure has trigonal pyramidal shape according to its molecular geometry and tetrahedral shape according to its electron geometry.

PBr3 Hybridization

The hybridisation of any structure is based on its steric number. Hybridization of PBr3 lewsi structure is based on the steric number on its central phosphorous atom.

The addition of total number of bonded elements associated with central atom and its lone electron pairs is the steric number.

Steric number of PBr3 = (no. of bonded elements or atoms attached with phosphorous + phosphorous atom lone pair of electrons)

As in the above PBr3 lewis structure, central P atom has one lone pair electron and it is connected with three Br atoms.

 So, PBr3 steric number = 3 (attached 3Br) + 1 (lone pair electron) = 4

Thus, calculated steric number is four for PBr3 lewis structure, therefore there is Sp3 hybridization in PBr3 lewis structure.

PBr3 lewis structure resonance

If you would like to draw the PBr3 resonance structure, so it is impossible to draw the resonance structure of PBr3 molecule because there is no any formal charge on PBr3 molecule and also it does not contain any double or triple bond in PBr3 lewis structure. There is a zero formal charge on PBr3 molecule and central phosphorous atom have three single covalent bonds joined with three bromine atoms contains sigma bonds. Also central phosphorous has one lone electron pair and bromine atoms has complete octet in PBr3 lewis structure.

That’s why PBr3 molecule is a stable molecule that cannot form any resonance hybrid structure.

PBr3 polar or nonpolar

When the elements get combine to form any structure, there is the formation of bonds to make any structure and sometimes the bond formed between the elements of different electronegativities. Due to these there is a separation of electric charges and causing partial positive charge and negative charge on the atoms which results in the polarity forming diploe moment.

If there is zero charge separation means the atoms of structure has difference in its electronegativity or the charge gets cancel out one another in that molecule. So, it has totally zero dipole moment and has non-polar nature.

 In PBr3 lewis structure, electronegativity of phosphorous atom is 2.19 and electronegativity of bromine atom is 2.96. So, the difference of electronegativities of P and Br is 0.77 and it is a big difference. Therefore, there is a formation of polar bonds among P and Br creating partial positive charge on P atom and partial negative charge on three Br atoms.

As we already know that the PBr3 molecule has trigonal pyramidal shape considering it is asymmetrical molecule. Therefore, the dipole moment does not cancel out one another and PBr3 comes under polar molecule. So, we can say that the PBr3 molecule is polar in nature as it has asymmetrical shape.

PBr3 lewis structure bond angle

Usually, molecules having tetrahedral geometry and containing one central atom surrounded by three elements has bond angles 109.5 degree. But in PBr3 lewis structure, it is an asymmetrical molecule and has a lone electron pair on P atom. So the bond angle could not be equal but it can be nearly 109.5 degree.

PBr3 lewis structure showing bond angle between P and Br atoms

The PBr3 bond angle is less than 109.5 degree due to the repulsion cause by lone electron pairs on Br-P-Br bonds which decreases its original bond angle. So, as the lone pair takes more space than bond pairs the PBr3 bond angle could be 101 degree.

PBr3 Uses

  • Phosphorous tribrimide is used in the formation of alkyl bromides.
  • In organic chemistry PBr3 is used as an brominating agent.
  • PBr3 is used in the analysis of oxygen and sugar.
  • PBr3 is also used in various syntheses as a catalyst.
  • PBr3 is also used as a fire suppressant compound for Halon 1301.

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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