Albr3 Lewis Structure,Geometry:9 Facts You Should Know

 In this article we are discussing about Albr3 lewis structure and geometry and 9 facts regarding this.

Albr3 is composed of central Al and 3 Br atoms. It has the molecular weight of 266.694. It is colorless and hygroscopic in nature. It is a pungent smell pale yellow solid.

Albr3 lewis structure drawing

As Al is bigger in size and has less electronegativity than Br atom, Al act as the central atom in this compound. Al has 3 valance electrons by the use of which it can form 3 sigma bonds with 3 Br atoms.

There is total of 7 electrons in valance shell of Br atom and out of this 7 electrons only 1 is used to form covalent bond with Al atom and 6 remaining electrons present as lone electrons.

Albr3 lewis structure resonance

Resonance is a process in which movement of electrons occurs from atom to atom by delocalization of electrons. Albr3 possess 3 resonance structures.

In all the structures Al-Br bond has partial double bond character due to delocalization of electron pair that present on Br atom with the vacant p orbital of Al atom to form p∏-p∏ back bonding.

Albr3 lewis structure Resonance

Albr3 lewis structure shape

According to VSEPR theory the shape of Albr3 is trigonal planer in which central Al is surrounding by 3 Br atoms. As lone pair is absent on Al atom the geometry of this compound is ideal trigonal planer.

This is because all the valance shell electrons of Al atom take part in covalent bonding with Br atom, hence there exist on lone pair of electron on central Al atom.

Albr3 lewis structure formal charge

The formal charge of an atom in a compound can be determined by the following formula:

Formal Charge (f) = Total No of valance electrons- (No of bonding electrons)/2- Total No of nonbonding electrons.

Hence formal charge on Al atom in Albr3=3-6/2-0=0

Formal charge on each Br atom in Albr3=7-2/2-6=0.

We see that formal charge on central Al atom and each Br atom is 0 making the whole compound is neutral.

Albr3 lewis structure angle

In Albr3 Al uses sp2 hybrid orbitals to form Albr3. The structure of Albr3 is trigonal planner. As it is not a distorted structure the bond angle found in Albr3 is exactly 1200.

The distortion is bond angle does not occur due to absence of lone pair of electron in the central Al atom. The bond angle in Albr3 suggested that all the atoms in Albr3 are present in same plane.

Albr3 lewis structure octet rule

In the lewis structure of Albr3 we found that each Br atom has 8 electrons in its valance shell and fulfill their octet. In Albr3 Al forms 3 covalent sigma bonds with Br atom and each bond contains 2 electrons.

There are a total 6 electrons in the valance shell of Al atom, hence it can’t fulfill their octet. Hence according to octet rule Albr3 is a unstable compound.

Albr3 lewis Structure lone pairs

The formula with the help of which we can find the lone pair of electron on the given atom is given below:

No of lone pairs= Total no of valance electron of the atom-no of bonds formed by that atom.

In Albr3 lone pair present on Al atom= 3-3=0 i.e. 0 lone pair.

Lone pair present on each Br atom=7-1=6 i.e. 3 lone pair.

These lone pair of electrons is found In the lewis structure of Albr3 on the given atoms as electron dots.

Albr3 Valance Electrons

Firstly to find out the total valance electron in Albr3, it is important to know the electronic configuration of Al and Br atom. The electronic configuration of Al is [Ne] 3s2 3p1 and we see from electronic configuration that there are 3 electrons in valance shell of Al atom.

The electronic configuration of Br atom is [Ar] 4s2 3d10 4p5. There is 7 electrons in the valance shell of Br atom.. The total valance electrons that present on Albr3 will be equal to the (sum of the valance electron of Al and Br atom) i.e. equals to (3*1)+(7*3)=24. There are 24 valance electrons in Albr3.

Albr3 Hybridization

Hybridization is the process in which lower energy hybrid orbitals are formed by mixing of higher energy atomic orbitals. Al has valance shell electronic configuration 3s2 3p1. From electronic configuration of Al atom it can stated that only 1 unpaired electron present in p orbital and we must have 3 unpaired electrons to make Albr3.

In the excited state, Al transfer 2 electrons from 3s orbital to 3p orbital and now a total of 3 unpaired electron is present in central Al atom. After that 3 Br atom gave 3 unpaired electrons to form 3 electron pairs by which 3 Al-Br single covalent bond is formed and remaining 6 electrons on Br atom present as 3 lone pair of electrons. In this compound Br uses sp2 hybrid orbital to form Al-Br bonds.

Albr3 Hybridisation

Albr3 solubility

In Albr3 due to high electronegativity of Br atom Al-Br bond moments lies towards Br atom. The net dipole moment of Albr3 is 0, because Albr3 has planner structure in which 3 Al-Br bond moments cancel each other.

That is why Albr3 is nonpolar in nature. As it is nonpolar in nature it is soluble in nonpolar solvents e.g. diethyl ether, acetone. Although Albr3 is also soluble in methanol, as it is a polar solvent with low dielectric constant.


Due to large size of Br atom, p∏-p∏ back bonding found in Al-Br bond is not to too strong to make the compound octet fulfilled. That is why this compound is electron deficient and acts as a lewis acid. For this same reason Albr3 is an unstable compound. To release electron deficiency some times Albr3 dimerises to form Al2Br6 molecule.

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