How to draw PBr3 Lewis Structure? - Science Education and Tutorials

Q: What is the PBr3 Lewis structure?

PBr3 Lewis structure is dot representation

Q: What is the formal charge on the PBr3 Lewis structure?

Zero charges on the PBr3 molecular structure

The phosphorus tribromide chemical formula is PBr3. Drawing PBr3 Lewis Structure is very easy to by using the following method. Here in this post, we described step by step method to construct PBr3 Lewis Structure. The phosphorus and bromine elements come as the member of the nitrogen and halogen family groups from the periodic table respectively. The valence electrons in phosphorus and bromine are five and seven respectively. The branch of phosphorus halogen compound chemistry is used to make chemicals reagents for organic chemical reactions.

Table of Contents

Key Points To Consider When Drawing The PBr3 Electron Dot Structure

A three-step approach for drawing the PBr3 Lewis structure can be used. The first step is to sketch the Lewis structure of the PBr3 molecule, to add valence electrons around the phosphorus atom; the second step is to add valence electrons to the three bromine atoms, and the final step is to combine the step1 and step2 to get the PBr3 Lewis Structure.

The PBr3 Lewis structure is a diagram that illustrates the number of valence electrons and bond electron pairs in the PBr3 molecule. The geometry of the PBr3 molecule can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory), which states that molecules will choose the PBr3 geometrical shape in which the electrons have from one another.

Finally, you must add their bond polarities to compute the strength of the three P-Br single bonds (dipole moment properties of the PBr3 molecule). The phosphorus-bromine bonds in phosphorus tribromide(PBr3), for example, are polarised toward the more electronegative bromine in PBr3 molecule, and because both bonds have the same size and are located around three bromine terminals of the trigonal pyramidal with one lone pair (in total two electrons) on the phosphorus atom, their sum of dipole moment is nonzero due to the PBr3 molecule’s bond dipole moment and more electron polarity to the bromine atoms. Because each three P-Br bonds polarity not canceled each other in the PBr3 molecule due to the presence of one lone pair of electrons. The phosphorus tribromide(PBr3) molecule is classified as a polar molecule.

The molecule of phosphorus tribromide (with trigonal pyramidal molecular geometry) is tilted, the bond angles between phosphorus and bromine are 101.5 degrees. It has a difference in electronegativity values between phosphorus and bromine atoms, with central phosphorus’s pull being less than terminal bromine’s in the PBr3 molecule. But they not canceled each other due to the asymmetrical trigonal pyramidal with one lone pair in the molecular geometry of the PBr3 molecule.

As a result, it has the nonzero dipole moment. The PBr3 molecule has a nonzero dipole moment due to an unequal charge distribution of negative and positive charges. But both phosphorus and bromine atoms fall on the nitrogen and halogen family groups in the periodic table respectively. The bromine atom is a more electronegative value than phosphorus in the PBr3 molecule. The PBr3 molecule has the net dipole moment of 0.66D value in the ground state energy state.

PBr3 molecule has three P-Br single bonds. Its dipole moment in the ground state is totally different as compared with the excited state. If it absorbs light may be from visible or UV light. It undergoes pi to pi star and n to pi star transition from ground state energy level to excited state energy level. In the excited state energy level, the PBr3 molecule shows a definite dipole moment. But it is very dynamics.

Molecules can be classified as polar or nonpolar. The molecule polar behaves in a different manner as compared to nonpolar.

Overview: PBr3 Lewis Structure

The central atom is phosphorus, which is bordered on three terminals with bromine atoms( in trigonal pyramidal geometry), and one lone pair on the central phosphorus atom in the trigonal pyramidal molecular geometry. Phosphorus has five outermost valence electrons, indicating that it possesses five electrons in its outermost shell, whereas bromine also has seven valence electrons in its outermost shell. To complete the octet of the phosphorus and bromine atoms requires three and one valence electrons on each of their outermost shell respectively.

Three bromine atoms establish covalent connections with the central phosphorus atom as a result, leaving the phosphorus atom with one lone pair. There is one lone pair of electrons on the phosphorus central atom that resists the bond pairs of the three P-Br bonds. According to VSEPR theory, the single P-Br bond pairs polarity lead the PBr3 molecule to take on the trigonal pyramidal geometry structure.

The PBr3 molecule’s three P-Br bonds are arranged in symmetrical polarity order around the trigonal pyramidal molecular geometry, giving rise to the PBr3 molecular shape. The PBr3 molecule has a trigonal pyramidal molecular geometry because there is an electrical repulsion between the lone pairs of electrons in phosphorus and three single bond pairs(P-Br) of the PBr3 molecule.

Lewis structure of PBr3 has dot electron representative structure. Valence electrons of atoms undergo orbitals mixing in the chemical reactions, gives new types of molecular species of PBr3. The molecule is nothing but a bundle of valence electrons from the atoms. But it is converted to bond pairs and lone pairs in the molecular structure.

Electronegative value Difference Calculation of PBr3 Molecule:

Phosphorus and bromine Electronegative difference in PBr3:

The phosphorus atom has an electronegativity of 2.19, while bromine has an electronegativity of 2.96 in the PBr3 molecule. The difference in electronegativity of phosphorus and bromine can be estimated using the method below.

The electronegative value difference between phosphorus and bromine in PBr3 molecule
Electronegativity value of phosphorus = 2.19
Electronegativity value of bromine= 2.96
Difference of electronegativity value between phosphorus and bromine in PBr3 molecule = 2.96 – 2.19 = 0.77
Electronegativity difference between P-Br bond calculation of PBr3 molecule

The electronegative difference between phosphorus and bromine is greater than 0.5. This indicated the bond polarity moves near to polar nature. P-Br bond polarity in the PBr3 molecule is polar.

Because of this difference in electronegativity of phosphorus and bromine atoms, the PBr3 molecule’s P-Br bond becomes polar. The total net dipole moment of the PBr3 molecule is nonzero due to the noncancellation of the bond dipole moment in the trigonal pyramidal geometry. The electronegativity of an atom is the strength with which it may attract bound electron pairs to its side. The polarity of PBr3 is discussed in our previous post.

As a result, the P-Br bond’s dipole moment is high due to the polarization of the bonds and one lone pair of electrons on phosphorus, and all P-Br bonds’ dipoles are arranged in the asymmetrical PBr3 molecular geometry. The PBr3 molecule has a nonzero net dipole moment.

The electron dot structure of the PBr3 molecule is also known as the PBr3 Lewis structure. It determines the number of outermost valence electrons as well as the electrons engaged in the PBr3 molecule’s bond formation. The outermost valence electrons of the PBr3 molecule must be understood while considering the Lewis structure of the molecule.

The phosphorus atom is the middle element in PBr3 molecular geometry, with five electrons in its outermost valence electron shell, whereas the bromine atom has seven electrons in its outermost valence electron shell. The bromine atom has seven valence electrons.

The PBr3 has a total of 26 valence electrons as a result of the foregoing above-said reasoning. With the core central phosphorus atom, the three terminals with three bromine atoms form covalent bonds, leaving the phosphorus atom with one lone pair in the middle of trigonal pyramidal geometry.

Because lone pairs on the terminal bromine atoms create interaction with P-Br bond pairs(but it is negligible in the ground state of the PBr3 molecule). The bond angle of the Br-P-Br bond in the trigonal pyramidal molecular geometry is approximately 101.5 degrees. This angle is less than the CH4 molecule bond angle. The P-Br bond length is 222pm(picometer).

To sketch the PBr3 Lewis structure by following these instructions:

Step-1: PBr3 Lewis dot Structure by counting valence electrons on the phosphorus atom

To calculate the valence electron of each atom in PBr3, look for its periodic group from the periodic table. The nitrogen and halogen group families, which are the 15th and 17th groups in the periodic table, are both made up of phosphorus and bromine atoms respectively. In their outermost shells, bromine and phosphorus have seven and five valence electrons respectively.

Calculate the total number of valence electrons in the PBr3 molecule’s outermost valence shell. The first step is to determine how many electrons are in the PBr3 Lewis structure’s outermost valence shell. An electron in an atom’s outermost shell is known as a valence electron. It is represented by dots in the PBr3 Lewis diagram. The PBr3 molecule’s core phosphorus atom can be represented as follows:

Total outermost valence shell electron of phosphorus atom in PBr3= 5
Total outermost valence shell electron of bromine atom in PBr3= 7
The PBr3 molecule has one central phosphorus and three bromine atoms. Then the total outermost valence shell electrons can be calculated as follows
∴ Total outermost valence shell electrons available for PBr3 Lewis structure( dot structure) = 5+3*7= 26 valence electrons in PBr3.
calculation of total valence electron of PBr3 molecule

Choose the atom with the least electronegative value atom and insert it in the center of the molecular geometry of PBr3. We’ll choose the least electronegative value atom in the PBr3 molecule to place in the center of the PBr3 Lewis structure diagram in this phase. The electronegativity value in periodic groups grows from left to right in the periodic table and drops from top to bottom.

The first step is to put five valence electrons around the phosphorus atom as given in the figure.

Step-2: Lewis Structure of PBr3 for counting valence electrons around the terminal bromine atoms

As a result, phosphorus is the second atom in the periodic table’s nitrogen family group. Bromine is the third member of the halogen family. The electronegative value of the bromine atom is higher than that of the phosphorus atom in the PBr3 molecule. Furthermore, bromine has a seven electrons limit since phosphorus is the less electronegative element in the PBr3 molecule.

In the PBr3 Lewis structure diagram, the phosphorus atom can be the center atom of the molecule. As a result, central phosphorus in the PBr3 Lewis structure, with all three bromine atoms arranged in a trigonal pyramidal geometry.

Add valence electrons around the bromine atom, as given in the figure.

Step-3: Lewis dot Structure for PBr3 generated from step-1 and step-2

Connect the exterior and core central atom of the PBr3 molecule with three single P-Br bonds. In this stage, use three bromine atoms on the outside of the PBr3 molecule to the central phosphorus atom in the middle.

Count how many electrons from the outermost valence shell have been used in the PBr3 structure so far. Each P-Br single bond carries two electrons because each phosphorus atom is connected to three bromine atoms by three P-Br single bonds. Bond pairings of P-Br are what they’re called.

So, out of the total of 26 valence electrons available for the PBr3 Lewis structure, we used six electrons for the PBr3 molecule’s three P-Br single bonds. The PBr3 molecule has one lone pair of electrons in the central phosphorus atom.

Place the valence electrons in the P-Br bond pairs starting with the core phosphorus, three bromine atoms in the PBr3 molecule. In the PBr3 Lewis structure diagram, we always begin by introducing valence electrons from the central phosphorus atom(in step1). As a result, wrap around the central phosphorus atom’s bond pair valence electrons first (see figure for step1).

The phosphorus atom in the molecule gets only 8 electrons around its molecular structure. This central phosphorus atom is octet stable. But it has one lone pair. Phosphorus is a brownish solid in nature. Phosphorus catch fire in the exposure to air. But phosphorus is used in matchboxes and firecrackers.

Bromine(Br2) is in the gaseous liquid state at normal temperature and pressure. It is used as a brominating agent in the field of organic chemistry. It is a highly corrosive gaseous liquid. It is responsible for dry corrosion in the metal bodies. It is very reactive to bio-micro organisms.

Phosphorus requires 8 electrons in its outermost valence shell to complete the molecular octet stability, six electrons bond pairs in three P-Br single bonds, and one lone pair in the central phosphorus atom. Then lone pair of electrons on the bromine atoms of the PBr3 molecule is placed in a trigonal pyramidal geometry. Phosphorus already shares 8 electrons to the three P-Br single bonds. Then place the valence electron in the bromine atoms, it placed around seven electrons on each atom(step-2). 18 valence electrons were placed around three bromine atoms as lone pairs of electrons.

We’ve positioned 18 electrons around the three-terminal bromine atoms(step-3), which is represented by a dot, in the PBr3 molecular structure above. The phosphorus atom completes its molecular octet stability in the PBr3 molecule because it possesses six electrons in its (three P-Br single bonds) bond pairs with three bromine in the outermost valence shell.

Count how many outermost valence shell electrons have been used so far using the PBr3 Lewis structure. three electron bond pairs are shown as dots in the PBr3 chemical structure, whereas three single bonds each contain two electrons. The outermost valence shell electrons of the PBr3 molecule(bond pairs) are six as a result of the calculation. The total valence electron in a phosphorus atom is 8.

So far, we’ve used 26 of the PBr3 Lewis structure’s total 26 outermost valence shell electrons. One lone pair of electrons on the phosphorus atom in the trigonal pyramidal geometry of the PBr3 molecule.

Complete the middle phosphorus atom stability and, if necessary, apply a covalent bond. The central phosphorus atom undergoes octet stability(due to three single bond pairs of electrons).

The core atom in the PBr3 Lewis structure is phosphorus, which is bonded to the three bromine atoms by single bonds (three P-Br). With the help of three single bonds, it already shares 8 electrons. As a result, the phosphorus follows the octet rule and has 8 electrons surrounding it on the three terminals of the PBr3 molecule’s trigonal pyramidal geometry.

How to calculate the formal charge on phosphorus and bromine atoms in PBr3 Lewis Structure?

Calculating formal charge on the phosphorus of PBr3 molecule:

The formal charge on the PBr3 molecule’s phosphorus central atom often corresponds to the actual charge on that phosphorus central atom. In the following computation, the formal charge will be calculated on the central phosphorus atom of the PBr3 Lewis dot structure.

To calculate the formal charge on the central phosphorus atom of the PBr3 molecule by using the following formula:
The formal charge on the phosphorus atom of PBr3 molecule= (V. E(P)– L.E(P) – 1/2(B.E))
V.E (P) = Valence electron in a phosphorus atom of PBr3 molecule
L.E(P) = Lone pairs of an electron in the phosphorus atom of the PBr3 molecule.
B.E = Bond pair electron in P atom of PBr3 molecule
calculation of formal charge on phosphorus atom in PBr3 molecule

The phosphorus core atom (three single bonds connected to three bromine atoms ) of the PBr3 molecule has five valence electrons, one lone pair of electrons(two electrons), and six bonding pairing valence electrons. Put these values for the phosphorus atom in the formula above.

Formal charge on phosphorus atom of PBr3 molecule = (5- 2-(6/2)) =0

In the Lewis structure of PBr3, the formal charge on the central phosphorus atom is zero.

Calculating formal charge on the bromine atom of PBr3 molecule:

The formal charge on the PBr3 molecule’s bromine terminal atoms often corresponds to the actual charge on that bromine terminal atoms. In the following computation, the formal charge will be calculated on the terminal bromine atom of the PBr3 Lewis dot structure.

To calculate the formal charge on the terminal bromine atom of the PBr3 molecule by using the following formula:
The formal charge on the bromine atom of PBr3 molecule= (V. E(Br)– L.E(Br) – 1/2(B.E))
V.E (Br) = Valence electron in a bromine atom of PBr3 molecule
L.E(Br) = Lone pairs of an electron in the bromine atom of the PBr3 molecule.
B.E = Bond pair electron in Br atom of PBr3 molecule
calculation of formal charge on bromine atom in PBr3 molecule

The bromine terminal atoms of the PBr3 molecule have seven valence electrons, three lone pairs of electrons(six electrons), and two bonding pairing valence electrons(single bond). Put these values for the bromine atom in the formula above.

Formal charge on bromine atom of PBr3 molecule = (7- 6-(2/2)) =0

In the Lewis structure of PBr3, the formal charge on the terminal bromine atom is zero.

Summary:

In this post, we discussed the method to construct the PBr3 Lewis structure. First, the valence electrons are placed around the phosphorus atom. Second, place the valence electron on the bromine atoms. Finally, when we combined the first and second steps. It gives PBr3 Lewis structure. Need to remember that, if you follow the above-said method, you can construct molecular dot structure very easily.