AsBr3 Lewis Structure,Geometry:13 Facts You Should Know


In this article, we should discuss the AsBr3 lewis structure, mode of bonding, hybridization, geometry, shape, bond angle, and relevant detailed fact.

Arsenic tribromide is an inorganic covalent molecule where the central Arsenic atom is surrounded by 3 Br atoms in trigonal pyramidal geometry. The mode hybridization of the molecule is sp3. The bond angle of the molecule that is Br-As-Br bond angle is around 99.80 which deviated from the ideal bond angle due to lone pair repulsion.

AsBr3 is a colorless solid crystal trihalogenated compound of Arsenic. The molecule will show higher diamagnetic susceptibility. Due to the availability of a vacant d orbital of As, it behaves as a π-acidic ligand, and the lone pair also be donated

Some facts about Arsenic tribromide

The molar mass of AsBr3 is 314.634 g/mol and the boiling point and melting point of this molecule are 494 K and 304.2 K respectively. It has a higher refracting Index of 2.3.

In presence of elemental S, direct bromination of Arsenic oxide gives Arsenic tribromide.

2As2O3 + 3 S + 6 Br2 = 4 AsBr3 + 3SO2

1.    How to draw AsBr3 lewis structure

With the help of the lewis structure, the number of valence electrons, the number of electrons participating in bonding, formal charge, etc can be determined for the AsBr3 molecule.

in AsBr3 lewis structure taking the consideration of all the valence electrons of As and Br will be added together. Then we need to identify the central atom which is on the basis of electronegativity, so here Arsenic is the central atom (Br is more electronegative). Now As and three Br atoms are attached by single bond only and lone pairs are assigned on As, as octet is complete so no need to add double or multiple bonds.

2.    AsBr3 lewis structure shape

In the AsBr3 lewis structure, the electron density is present on the central As and there will be three bond pairs with three Br atoms and one lone pair. In this case Arsenic tribromide, the structure is trigonal pyramidal. In trigonal pyramidal structure, 3 Br atoms are surrounded by the Arsenic from three vertices.

3.    AsBr3 lewis structure valence electrons

In the AsBr3 lewis structure, Arsenic is attached by three Br atoms via three single bonds.   

The  ground state electronic configuration of Arsenic is 1s22s22p63s23p63d104s24p3 and for Bromine is 1s22s22p63s23p63d104s24p5, so the valence electrons  As and each Br atom are five and seven  respectively. So, the total number of valence electrons for the AsBr3 molecule which are involved in bond formation is 5 +  (7*3) =26.

AsBr3 Lewis Structure Valence Electrons

4.    AsBr3 lewis structure formal charge

The charge over a molecule taking into consideration of all atoms should have the same electronegativity is called the formal charge of a molecule.

The common formula for calculation of formal charge is, F.C. = Nv – Nl.p. -1/2 Nb.p.

Where Nv is the number of electrons in the valence shell, 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.

So, the formal charge of the AsBr3 lewis structureis 5-2-(6/2) = 0 [ valence electrons of central As are 5, 6 electrons participate in bond formation with three Br atoms, the lone pair electrons of As is 2]

5.    AsBr3 lewis structure lone pairs

The number of lone pairs should be calculated as the sum of the total number of lone pairs of every atom only that contains lone pairs, after the successful bond formation.

AsBr3 Lone Pairs

From the above AsBr3 lewis structure, it is evident that Arsenic contains 1 pair of lone pairs while 3 Bromine each contains 3 pairs of lone pairs.

So, the total number of lone pairs in Arsenic tribromide is = 1+(3*3) =10

6.    AsBr3 lewis structure octet rule

In the AsBr3 lewis structure, we see Arsenic is a group of VA elements so it has 5 valence electrons and Bromine is a VIIA element so It has 7 valence electrons.

So, Arsenic needed 3 electrons to complete its octet, and bromine needed 3 electrons to fulfill its octet. So, both As and Br undergo hybridization to form new four hybrid orbital and share electrons to fulfill their octet.

7.    AsBr3 lewis structure Bond Angle

From the VSEPR (Valence Shell Electron Pair Repulsion) theory, if the molecule of type AX3 has a bond angle is 1200 or has lone pair then the bond angle will be 109.50.

Bond Angle Of AsBr3

In the AsBr3 lewis structure, the bond angle of AsBr3 is neither 1200 nor 109.50, but the actual angle between Br-As-Br is 99.80 due to the repulsion of 3 large Br atoms with an Arsenic atom. Though As is large in size but there will be 3 large Br atoms and there will be massive lone pairs- lone pair repulsion, so to minimize this repulsion the molecule reduces its bond angle to 99.80.

8.    AsBr3 lewis structure Resonance

Delocalization of electrons cloud is called resonance.

Resonance Structure of AsBr3

In the AsBr3 lewis structure of resonance the most contributing structure is II or III as they contain a more covalent bond, but less electronegative atom Arsenic gets a negative charge this is also a destabilization factor but we should check the skeleton which contains a higher number of bonds in different resonance structures.

9.    AsBr3 Hybridization

The mixture of orbitals to form one or more new hybrid orbitals is called hybridization. Actually, to maintain the same energy level every atomic orbital undergoes hybridization.

The hybridization of any molecule is calculated by the formula

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=cation, A=anion

So, in the AsBr3 lewis structure, the number of valence electrons in the central atom is 5 and the number of monovalent atoms surrounded is 3 Br.

So, the hybridization is H=1/2 (5+3+0+0)=4 (sp3)

StructureHybridization  state of hybridization of central atom  Bond angle
Linear       2        sp /sd / pd          1800
Planner trigonal3                sp2                 1200
Tetrahedral   4                  sd3/ sp3               109.50
Trigonal bipyramidal    5                   sp3d/dsp3                 900 (axial), 1200(equatorial)
Octahedral     6                               sp3d2/ d2sp3               900
Pentagonal bipyramidal 7                  sp3d3/d3sp3                    900,720

                                 

From the above table if the hybridization number is 4 then the molecule is sp3 hybridized along with the lone pair.

In the ground state, the electronic configuration of Arsenic is [Ar]3d104s24p3 and bromine is [Ar]3d104s24p5. So, here 4s and 4p orbital of As as well as Br undergo hybridization to form a stable covalent molecule Arsenic tribromide. So here in hybridization, Arsenic contributes its one S orbital where lone pair is present and three P orbitals which make the bond with three Br. So, the hybridization of Arsenic tribromide is sp3.

10.      AsBr3 Solubility

From the AsBr3 lewis structure, we can’t predict the solubility of Arsenic tribromide.

As AsBr3 is a covalent molecule, so it has less ionic character and the ionization is very low, So, it has a lower solubility in polar solvents like water, but it has a greater solubility in hydrocarbons like ether, methanol, etc.

11.       Is AsBr3 acidic or basic?

From the evidence of the AsBr3 lewis structure, we can say that it is a moderate strong lewis acid.

In arsenic tribromide, there is a vacant orbital in Arsenic to accept lone pair or electron density from any lewis base, so it acts as lewis acid, But As also contains lone pair but they are not available for donation as As is surrounded by 3 electronegative Br atoms, they pull electron density from As to their site, so it is very difficult for As to donate that lone pair and again due the 3 electronegative atoms the accessibility of vacant orbital is very high so AsBr3 behaves as a lewis acid.

12.    Is AsBr3 ionic?

AsBr3 is a covalent molecule but it shows partial ionic character.

From Fajan’s rule we can say that there are 3 polarizable atoms Br is present and Arsenic easily polarize them, again from the ionic potential we can say that no molecule is not the pure covenant, so it has some % of ionic character.

13.    Is AsBr3 polar or nonpolar?

Yes, in the AsBr3 lewis structure, there is some resultant dipole moment is present in this molecule.

Dipole moment acts from less electronegative atom As towards more electronegative atom Br. Three Br presents different site of this molecule so they cannot cancel out each other dipole moment, so the molecule has some resultant dipole moment.

Summary

From the above discussion of the AsBr3 lewis structure, we can predict shape, geometry, bond angle, resonance, dipole moment, valence electrons even formal charge from the lewis dot formula and all the covenant molecules have some ionic character and there is no relation between the solubility of the molecule to its lewis structure.

                                                                              

                                                                                                       

                                                       

                                          

                                                                       

                                                                           

Biswarup Chandra Dey

Chemistry is not all about reading line by line and memorize, it is a concept to understand in easy way and here I am share with you the concept about chemistry which I learn because knowledge is worth to share it.

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