How to draw AlBr3 Lewis Structure? - Science Education and Tutorials

The Aluminium tribromide chemical formula is AlBr3. Drawing AlBr3 Lewis Structure is very easy to by using the following method. Here in this post, we described step by step method to construct AlBr3 Lewis Structure. The Aluminium and bromine elements come as members of the Aluminium and halogen family groups from the periodic table respectively. The valence electrons in Aluminium and bromine are three and seven respectively.

Table of Contents

Key Points To Consider When Drawing The AlBr3 Structure

A three-step approach for drawing the AlBr3 Lewis structure can be used. The first step is to sketch the Lewis structure of the AlBr3 molecule, to add valence electrons around the Aluminium 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 AlBr3 Lewis Structure.

The AlBr3 Lewis structure is a diagram that illustrates the number of valence electrons and bond electron pairs in the AlBr3 molecule. The geometry of the AlBr3 molecule can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory), which states that molecules will choose the AlBr3 geometrical shape in which the electrons have from one another.

Finally, you must add their bond polarities to compute the strength of the Al-Br bond (dipole moment properties of the AlBr3 molecule). The Aluminium-bromine bonds in Aluminium tribromide(AlBr3), for example, are polarised toward the more electronegative bromine in AlBr3 molecule, and because both bonds have the same size and are located around three bromine terminals of the trigonal planar with no lone pairs of electrons just out of the plan, their sum is zero due to the AlBr3 molecule’s bond dipole moment and no lone pairs of electrons on the Aluminium atom. Because each Al-Br bond polarity canceled each other in the AlBr3 molecule. The Aluminium tribromide(AlBr3) molecule is classified as a nonpolar molecule.

The molecule of Aluminium tribromide(with trigonal planar molecular geometry) is tilted, the bond angles between Aluminium and bromine are 120 degrees. It has a difference in electronegativity values between Aluminium and bromine atoms, with Aluminium’s pull being less than bromine’s terminal in the AlBr3 molecule. But they canceled each other due to the symmetrical molecular geometry of AlBr3. As a result, it has the zero dipole moment. The AlBr3 molecule has a zero dipole moment due to an equal charge distribution of negative and positive charges. The net dipole moment of the AlBr3 molecule is 0 D.

Overview: AlBr3 Lewis Structure

The central atom is Aluminium, which is bordered on three terminals with three bromine atoms( in trigonal planar geometry), and no lone pairs of electrons on the Aluminium in the trigonal planar geometry. Aluminium has three outermost valence electrons, indicating that it possesses three electrons in its outermost shell, whereas bromine only has seven valence electrons in its outermost shell. To complete the octet of the bromine atom, a bromine terminal atom requires one valence electron. If you’re interested in learning more about the bromine octet rule, please see our previous post.

Three bromine atoms establish covalent connections with the central Aluminium atom as a result, leaving the Aluminium atom with no lone pairs. There are no lone pair of electrons on the Aluminium central atom that resist the bond pairs of the three Al-Br. According to VSEPR theory, the bond pairs lead the AlBr3 molecule to take on a trigonal planar molecular geometry shape.

The AlBr3 molecule’s Al-Br bonds are arranged in symmetrical order around the trigonal planar molecular geometry, giving rise to the AlBr3 molecular shape. The AlBr3 molecule has a trigonal planar molecular geometry because there is no electrical repulsion between lone pairs and three bond pairs(Al-Br) of the AlBr3 molecule.

Electronegative Difference Calculation of AlBr3 Molecule:

The Aluminium atom has an electronegativity of 2.04, while bromine has an electronegativity of 2.96 in the AlBr3 molecule. The difference in electronegativity can be estimated using the method below.

The electronegative value difference between Aluminium and bromine
Electronegativity value of Aluminium = 2.04
Electronegativity value of bromine= 2.96
Difference of electronegativity value between Aluminium and bromine= 2.96 – 2.04=0.92
Electronegativity difference between Al-Br bond calculation of AlBr3 molecule

Due to the difference in electronegativity value of greater than 0.5, the Al-Br bond of the BBr3 molecule becomes polar. Because of this difference in electronegativity, the AlBr3 molecule’s Al-Br bond becomes polar. The total net dipole moment of the AlBr3 molecule is zero due to the cancellation of the bond dipole moment in the trigonal planar geometry. The electronegativity of an atom is the strength with which it may attract bound electron pairs to its side. The polarity of BF3 is discussed in our previous post.

As a result, the Al-Br bond’s dipole moment is high due to the polarization of the bonds and no lone pairs of electrons, and all Al-Br bonds’ dipoles are arranged in the symmetrical AlBr3 molecular geometry. The AlBr3 molecule’s total dipole moment is predicted to be 0 D. It has a partial negative charge for the terminal bromine atoms and a partial positive charge for the central Aluminium atom.

The electron dot structure of the AlBr3 molecule is also known as the AlBr3 Lewis structure. It determines the number of outermost valence electrons as well as the electrons engaged in the AlBr3 molecule’s bond formation. The outermost valence electrons of the AlBr3 molecule must be understood while considering the Lewis structure of the molecule.

The Aluminium atom is the middle element in AlBr3 molecular geometry, with three electrons in its outermost valence electron shell, whereas the bromine atom has seven electrons in its outermost valence electron shell.

The AlBr3 molecule has a total of 24 valence electrons as a result of the foregoing above-said reasoning. With the core central Aluminium atom, the three-terminal with three bromine atoms forms covalent bonds, leaving the Aluminium atom with no lone pairs of electrons on the top and bottom of trigonal planar geometry.

Because no lone pairs of electrons on the central Aluminium atom create interaction with Al-Br bond pairs. The bond angle of the Br-Al-Br bond in the trigonal planar molecular geometry is approximately 120 degrees. This angle is greater than the CH4 molecule bond angle due to the no lone pairs of electrons on the AlBr3 molecule.

There are two types of bonds in the AlBr3 molecule. The resonance structure of the AlBr3 molecule creates a double bond and a single bond. The double bond of Al-Br is shorter as compared to the single bond of Al-Br. The Al-Br bond length of the single bond of AlBr3 is longer than the Al-Cl bond length of AlCl3.

To sketch the AlBr3 Lewis structure by following these instructions:

Step-1: AlBr3 Lewis dot Structure by counting valence electrons on the Aluminium atom

To calculate the valence electron of each atom in AlBr3, look for its periodic group from the periodic table. The halogen and Aluminium families, which are the 17th and 13th groups in the periodic table, are both made up of bromine and Aluminium atoms. In their outermost shells, bromine and Aluminium have seven and three valence electrons, respectively.

Because bromine and Aluminium are members of the periodic table’s halogen and Aluminium family groups, their valence electrons are seven and three, respectively.

Calculate the total number of valence electrons in the AlBr3 molecule’s outermost valence shell. The first step is to determine how many electrons are in the AlBr3 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 AlBr3 Lewis diagram. The AlBr3 molecule’s core Aluminium atom can be represented as follows:

Total outermost valence shell electron of Aluminum atom in AlBr3= 3
Total outermost valence shell electron of the bromine atom in AlBr3= 7
The BC3 molecule has one central Aluminium and three bromine atoms. Then the total outermost valence shell electrons can be calculated as follows
∴ Total outermost valence shell electrons available for AlBr3 Lewis structure( dot structure) = 3+3*7= 24 valence electrons in AlBr3.
calculation of total valence electron of AlBr3 molecule

Choose the atom with the least electronegative value atom and insert it in the center of the molecular geometry of AlBr3. We’ll choose the least electronegative value atom in the AlBr3 molecule to place in the center of the AlBr3 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.

Step-2: Lewis Structure of AlBr3 for counting valence electrons around the terminal bromine atom

As a result, Aluminium is the second atom in the periodic table’s Aluminium family group. Aluminium is the first member of the Aluminium family. The electronegative value of the Aluminium atom is lower than that of the bromine atom in the AlBr3 molecule. Furthermore, Aluminium has a three electrons limit since bromine is the most electronegative element in the AlBr3 molecule.

In the AlBBr3 Lewis structure diagram, the Aluminium atom can be the center atom of the molecule. As a result, central Aluminium in the AlBr3 Lewis structure, with all three bromine arranged in the trigonal planar geometry.

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

Step-3: Lewis dot Structure for AlBr3 generated from step-1 and step-2

Connect the exterior and core central atom of the AlBr3 molecule with three single bonds (Al-Br). In this stage, use three bromine atoms on the outside of the AlBr3 molecule to the central Aluminium atom in the middle.

Count how many electrons from the outermost valence shell have been used in the AlBr3 structure so far. Each Al-Br bond carries two electrons because each Aluminium atom is connected to three bromine atoms by three Al-Br bonds. Bond pairings of Al-Br are what they’re called.

So, out of the total of 24 valence electrons available for the AlBr3 Lewis structure, we used 6 for the AlBr3 molecule’s three Al-Br bonds. The AlBr3 molecule has no lone pairs of electrons in the central Aluminium atom. We need to put extra electrons in the molecular geometry of AlBr3. Where to place the extra electron in the AlBr3 molecule?

Place the valence electrons in the Al-Br bond pairs starting with the core Aluminium, three bromine, and no lone pairs of electrons in the AlBr3 molecule. In the AlBr3 Lewis structure diagram, we always begin by introducing valence electrons from the central Aluminium atom(in step1). As a result, wrap around the central Aluminium atom’s bond pair valence electrons first (see figure for step1).

The Aluminium atom in the molecule gets only six electrons around its molecular structure. This central Aluminium atom is octet deficient. AlBr3 molecule goes on resonance. A bromine atom has three pairs of lone pairs of electrons. Due to the back bonding mechanism of Al-Br of the AlBr3 molecule, bromine gives one lone pair of electrons to the bond pairs of Al-Br bond. This makes a single bond into a double bond.

This makes Aluminium negative in charge and bromine makes positive in charge. The double bond resonated around the AlBr3 molecule. The double bond of Al-Br is shorter as compared to the single Al-Br bond. In this way, Aluminium gets its octet stability.

Aluminium requires 6 electrons in its outermost valence shell to complete the molecular stability, 6 electrons bond pairs in Al-Br bonds. Then no electrons as a lone pair of electrons on the Aluminium atom of the AlBr3 molecule are placed in a trigonal planar geometry. Aluminium already shares 6 electrons to the three Al-Br bonds. Then place the valence electron in the bromine atom, it placed around seven electrons(step-2). Totally, 21 valence electrons were placed on the three bromine atoms of the AlBr3 molecule.

We’ve positioned 6 electrons around the central bromine atom(step-3), which is represented by a dot, in the AlBr3 molecular structure above. The Aluminium atom completes its molecular stability in the AlBr3 molecule because it possesses 6 electrons in its (Al-Br bond pairs with three bromine in the outermost valence shell.

Count how many outermost valence shell electrons have been used so far using the AlBr3 Lewis structure. Three electron bond pairs are shown as dots in the AlBr3 chemical structure, whereas three single bonds each contain two electrons. The outermost valence shell electrons of the AlBr3 molecule(bond pairs) are six as a result of the calculation.

So far, we’ve used six of the AlBr3 Lewis structure’s total 6 outermost valence shell electrons. No lone pairs of electrons on the Aluminium atom in the trigonal planar of the AlBr3 molecule.

Complete the middle Aluminium atom stability and, if necessary, apply a covalent bond. The central Aluminium atom undergoes octet stability(due to resonance structure). Because it has a total of 8 electrons in the outermost valence shell. Eight electrons come from one double bond pair of Al-Br and two single bond pairs of Al-Br on the Aluminium central atom of AlBr3.

The core atom in the AlBr3 Lewis structure is Aluminium, which is bonded to the three bromine atoms by single bonds (Al-Br). With the help of three single bonds, it already shares six electrons. As a result, the Aluminium follows the octet rule and has 8 electrons (due to resonance structure) surrounding it on the three terminals of the AlBr3 molecule’s trigonal planar geometry.

How to calculate the formal charge on a Aluminium atom in AlBr3 Lewis Structure?

The formal charge on the AlBr3 molecule’s Aluminium central atom often corresponds to the actual charge on that Aluminium central atom. In the following computation, the formal charge will be calculated on the central Aluminium atom of the AlBr3 Lewis dot structure.

To calculate the formal charge on the central aluminium atom of the AlBr3 molecule by using the following formula:
The formal charge on the aluminium atom of AlBr3 molecule= (V. E(Al)– L.E(Al) – 1/2(B.E))
V.E (Al) = Valence electron in a aluminium atom of AlBr3 molecule
L.E(Al) = Lone pairs of an electron in the aluminium atom of the AlBr3molecule.
B.E = Bond pair electron in Al atom of AlBr3 molecule
calculation of formal charge on aluminium atom in AlBr3 molecule

The aluminium core atom (three single bonds connected to three bromine atoms ) of the AlBr3 molecule has 3 valence electrons, no lone pairs of electrons(zero electrons), and six bonding pairing valence electrons. Put these values for the aluminium atom in the formula above.

Formal charge on aluminium atom of AlBr3 molecule = (3- 0-(6/2)) =0

In the Lewis structure of AlBr3, the formal charge on the central aluminium atom is zero.

Summary:

In this post, we discussed the method to construct the AlBr3 Lewis structure. First, the valence electrons are placed around the aluminium atom. Second, place the valence electron on the bromine atom. Finally, when we combined the first and second steps. It gives BBr3 Lewis structure. Need to remember that, if you follow the above-said method, you can construct molecular dot structure very easily.