How to draw AlCl3 Lewis Structure? - Science Education and Tutorials

The Aluminium trichloride chemical formula is AlCl3. Drawing AlCl3 Lewis Structure is very easy to by using the following method. Here in this post, we described step by step method to construct AlCl3 Lewis Structure. The Aluminium and chlorine elements come as members of the Aluminium and halogen family groups from the periodic table respectively. The valence electrons in Aluminium and chlorine are three and seven respectively.

Table of Contents

Key Points To Consider When Drawing The AlCl3 Structure

A three-step approach for drawing the AlCl3 Lewis structure can be used. The first step is to sketch the Lewis structure of the AlCl3 molecule, to add valence electrons around the Aluminium atom; the second step is to add valence electrons to the three chlorine atoms, and the final step is to combine the step1 and step2 to get the AlCl3 Lewis Structure.

The AlCl3 Lewis structure is a diagram that illustrates the number of valence electrons and bond electron pairs in the AlCl3 molecule. The geometry of the AlCl3 molecule can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory), which states that molecules will choose the AlCl3 geometrical shape in which the electrons have from one another.

Finally, you must add their bond polarities to compute the strength of the Al-Cl bond (dipole moment properties of the AlCl3 molecule). The Aluminium-chlorine bonds in Aluminium trichloride(AlCl3), for example, are polarised toward the more electronegative chlorine in AlCl3 molecule, and because both bonds have the same size and are located around three chlorine terminals of the trigonal planar with no lone pairs of electrons just out of the plan, their sum is zero due to the AlCl3 molecule’s bond dipole moment and no lone pairs of electrons on the Aluminium atom. Because each Al-Cl bond polarity cancelled each other in the AlCl3 molecule. The Aluminium trichloride(AlCl3) molecule is classified as a nonpolar molecule.

The molecule of Aluminium trichloride(with trigonal planar molecular geometry) is tilted, the bond angles between Aluminium and chlorine are 120 degrees. It has a difference in electronegativity values between Aluminium and chlorine atoms, with Aluminium’s pull being less than chlorine’s terminal in the AlCl3 molecule. But they canceled each other due to the symmetrical molecular geometry of AlCl3. As a result, it has the zero dipole moment. The AlCl3 molecule has a zero dipole moment due to an equal charge distribution of negative and positive charges. The net dipole moment of the AlCl3 molecule is 0 D.

Overview: AlCl3 Lewis Structure

The central atom is Aluminium, which is bordered on three terminals with three chlorine 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 chlorine only has seven valence electrons in its outermost shell. To complete the octet of the chlorine atom, a chlorine terminal atom requires one valence electron. If you’re interested in learning more about the chlorine octet rule, please see in our previous post.

Three chlorine 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-Cl. According to VSEPR theory, the bond pairs lead the AlCl3 molecule to take on a trigonal planar molecular geometry shape.

The AlCl3 molecule’s Al-Cl bonds are arranged in symmetrical order around the trigonal planar molecular geometry, giving rise to the AlCl3 molecular shape. The AlCl3 molecule has a trigonal planar molecular geometry because there is no electrical repulsion between lone pairs and three bond pairs(Al-Cl) of the AlCl3 molecule.

Electronegative Difference Calculation of AlCl3 Molecule:

The Aluminium atom has an electronegativity of 2.04, while chlorine has an electronegativity of 3.16 in the AlCl3 molecule. The difference in electronegativity can be estimated using the method below.

The electronegative value difference between Aluminium and chlorine
Electronegativity value of Aluminium = 2.04
Electronegativity value of chlorine= 3.16
Difference of electronegativity value between Aluminium and chlorine= 3.16 – 2.04=1.12
Electronegativity difference between Al-Cl bond calculation of AlCl3 molecule

Due to the difference in electronegativity value of greater than 0.5, the Al-Cl bond of the AlCl3 molecule becomes polar. Because of this difference in electronegativity, the AlCl3 molecule’s Al-Cl bond becomes polar. The total net dipole moment of the AlCl3 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-Cl bond’s dipole moment is high due to the polarization of the bonds and no lone pairs of electrons, and all Al-Cl bonds’ dipoles are arranged in the symmetrical AlCl3 molecular geometry. The AlCl3 molecule’s total dipole moment is predicted to be 0 D. It has a partial negative charge for the terminal chlorine atoms and a partial positive charge for the central Aluminium atom.

The electron dot structure of the AlCl3 molecule is also known as the AlCl3 Lewis structure. It determines the number of outermost valence electrons as well as the electrons engaged in the AlCl3 molecule’s bond formation. The outermost valence electrons of the AlCl3 molecule must be understood while considering the Lewis structure of the molecule.

The Aluminium atom is the middle element in AlCl3 molecular geometry, with three electrons in its outermost valence electron shell, whereas the chlorine atom has seven electrons in its outermost valence electron shell.

The AlCl3 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 chlorine 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-Cl bond pairs. The bond angle of the Cl-Al-Cl 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 AlCl3 molecule.

There are two types of bonds in the AlCl3 molecule. The resonance structure of the AlCl3 molecule creates a double bond and a single bond. The double bond of Al-Cl is shorter as compared to the single bond of Al-Cl. The Al-Cl bond length of the single bond is 175 pm(picometer).

To sketch the AlCl3 Lewis structure by following these instructions:

Step-1: AlCl3 Lewis dot Structure by counting valence electrons on the Aluminium atom

To calculate the valence electron of each atom in AlCl3, 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 chlorine and Aluminium atoms. In their outermost shells, chlorine and aluminium have seven and three valence electrons, respectively.

Because chlorine 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 AlCl3 molecule’s outermost valence shell. The first step is to determine how many electrons are in the AlCl3 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 AlCl3 Lewis diagram. The AlCl3 molecule’s core Aluminium atom can be represented as follows:

Total outermost valence shell electron of Aluminium atom in AlCl3= 3
Total outermost valence shell electron of the chlorine atom in AlCl3= 7
The AlC3 molecule has one central Aluminium and three chlorine atoms. Then the total outermost valence shell electrons can be calculated as follows
∴ Total outermost valence shell electrons available for AlCl3 Lewis structure( dot structure) = 3+3*7= 24 valence electrons in AlCl3.
calculation of total valence electron of AlCl3 molecule

Choose the atom with the least electronegative value atom and insert it in the center of the molecular geometry of AlCl3. We’ll choose the least electronegative value atom in the AlCl3 molecule to place in the center of the AlCl3 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 AlCl3 for counting valence electrons around the terminal chlorine 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 chlorine atom in the AlCl3 molecule. Furthermore, Aluminium has a three electrons limit since chlorine is the most electronegative element in the AlCl3 molecule.

In the AlCl3 Lewis structure diagram, the Aluminium atom can be the center atom of the molecule. As a result, central Aluminium in the AlCl3 Lewis structure, with all three chlorine arranged in the trigonal planar geometry.

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

Step-3: Lewis dot Structure for AlCl3 generated from step-1 and step-2

Connect the exterior and core central atom of the AlCl3 molecule with three single bonds (Al-Cl). In this stage, use three chlorine atoms on the outside of the AlCl3 molecule to the central Aluminium atom in the middle.

Count how many electrons from the outermost valence shell have been used in the AlCl3 structure so far. Each Al-Cl bond carries two electrons because each Aluminium atom is connected to three chlorine atoms by three Al-Cl bonds. Bond pairings of Al-Cl are what they’re called.

So, out of the total of 24 valence electrons available for the AlCl3 Lewis structure, we used 6 for the AlCl3 molecule’s three Al-Cl bonds. The AlCl3 molecule has no lone pairs of electrons in the central Aluminium atom. We need to put extra electrons in the molecular geometry of AlCl3. Where to place the extra electron in the AlCl3 molecule?

Place the valence electrons in the Al-Cl bond pairs starting with the core Aluminium, three chlorine, and no lone pairs of electrons in the AlCl3 molecule. In the AlCl3 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 aluminum atom is octet deficient. AlCl3 molecule goes on resonance. A chlorine atom has three pairs of lone pairs of electrons. Due to the back bonding mechanism of Al-Cl of the AlCl3 molecule, chlorine gives one lone pair of electrons to the bond pairs of Al-Cl bond. This makes a single bond into a double bond.

This makes Aluminium negative in charge and chlorine makes positive in charge. The double bond resonated around the AlCl3 molecule. The double bond of Al-Cl is shorter as compared to the single Al-Cl bond. In this way, aluminum gets its octet stability.

Aluminium requires 6 electrons in its outermost valence shell to complete the molecular stability, 6 electrons bond pairs in Al-Cl bonds. Then no electrons as a lone pair of electrons on the Aluminium atom of the AlCl3 molecule are placed in a trigonal planar geometry. Aluminium already shares 6 electrons to the three Al-Cl bonds. Then place the valence electron in the chlorine atom, it placed around seven electrons(step-2). Totally, 21 valence electrons were placed on the three chlorine atoms of the AlCl3 molecule.

We’ve positioned 6 electrons around the central chlorine atom(step-3), which is represented by a dot, in the AlCl3 molecular structure above. The Aluminium atom completes its molecular stability in the AlCl3 molecule because it possesses 6 electrons in its (Al-Cl) bond pairs with three chlorine in the outermost valence shell.

Count how many outermost valence shell electrons have been used so far using the AlCl3 Lewis structure. Three electron bond pairs are shown as dots in the AlCl3 chemical structure, whereas three single bonds each contain two electrons. The outermost valence shell electrons of the AlCl3 molecule(bond pairs) are six as a result of the calculation.

So far, we’ve used six of the AlCl3 Lewis structure’s total 6 outermost valence shell electrons. No lone pairs of electrons on the Aluminium atom in the trigonal planar of the AlCl3 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-Cl and two single bond pairs of Al-Cl on the Aluminium central atom of AlCl3.

The core atom in the AlCl3 Lewis structure is Aluminium, which is bonded to the three chlorine atoms by single bonds (Al-Cl). 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 AlCl3 molecule’s trigonal planar geometry.

How to calculate the formal charge on a Aluminium atom in AlCl3 Lewis Structure?

The formal charge on the AlCl3 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 AlCl3 Lewis dot structure.

To calculate the formal charge on the central Aluminium atom of the ALCl3 molecule by using the following formula:
The formal charge on the Aluminium atom of AlCl3 molecule= (V. E(Al)– L.E(Al) – 1/2(B.E))
V.E (Al) = Valence electron in a Aluminium atom of AlCl3 molecule
L.E(Al) = Lone pairs of an electron in the Aluminium atom of the AlCl3molecule.
B.E = Bond pair electron in Al atom of AlCl3 molecule
calculation of formal charge on Aluminium atom in AlCl3 molecule

The Aluminium core atom (three single bonds connected to three chlorine atoms ) of the AlCl3 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 AlCl3 molecule = (3- 0-(6/2)) =0

In the Lewis structure of AlCl3, the formal charge on the central Aluminium atom is zero.

Summary:

In this post, we discussed the method to construct the AlCl3 Lewis structure. First, the valence electrons are placed around the Aluminium atom. Second, place the valence electron on the chlorine atom. Finally, when we combined the first and second steps. It gives AlCl3 Lewis structure. Need to remember that, if you follow the above-said method, you can construct molecular dot structure very easily.