Aluminium trichloride or AlCl3 is a white colour powder with a molar mass of 133.34 g/mol. Let us explore the physical nature of AlCl3.
AlCl3 is an inorganic chemical compound with a low melting point of 180 °C and vapor pressure of 133.3 Pa (99 °C). It is hygroscopic as it interacts with water molecules and turned yellow sometimes which is an indication of impurities.
The important aspects of AlCl3 such as its structure formation, structural shape, hybridization and formal charges are explained in detail in the following parts of this article.
How to draw the AlCl3 lewis structure?
AlCl3 is a lewis acid. It is used in several pericyclic reactions as the catalyst. Let us see how to draw lewis dots for AlCl3 step by step as mentioned below.
1. Count the total number of valence electrons associated with AlCl3
For AlCl3, 24 valence electrons are present. Out of which, 3 are coming from the aluminium atom and the rest 21 come from the chlorine atoms.
2. Arrangement of the atoms
In the lewis structure of AlCl3 , the aluminum atom will place at the central position and the rest of the chlorine atoms surround it. According to the electronegativity rule, the more electronegative elements will place at the peripheral positions and less at the central position.
3. Drawing the lewis dots
Now, three lewis dots are drawn for the aluminium atom and the seven dots are assigned to the chlorine atoms as shown in the above figure. This is because lewis dots are representing the valence electrons of each atom.
4. Formation of bonds
Firstly, a single bond or sigma bond will be formed between the aluminium and chlorine atoms by using lewis dots. This happens because the sigma bond is formed always first.
AlCl3 lewis structure shape
The structural shape of any molecule gives information about the spatial arrangement of atoms within the molecule. Let us discuss the AlCl3 structural shape concept.
The shape of AlCl3 is trigonal planar. Since the central atom aluminium is bonded bond to three chlorine atoms in a triangle-like manner. Moreover, the absence of the lone pairs also favours this shape.
AlCl3 lewis structure formal charge
The total charge present over a molecule is called a formal charge. Let us calculate for AlCl3 structure.
The formal charge on AlCl3 is zero. This indicates that AlCl3 is stable because it carries a negligible formal charge.
The calculation for the formal charge for each atom is given below:
Formal charge = Total valence count – Lone pairs- No of bonded electrons.
| Atoms | Valence electrons | Unbonded electron count | Bonded electrons | Formal charge |
| Aluminium atom | 3 | 0 | 6 | 3-0-6/2 = 0 |
| Chlorine atom | 7 | 6 | 2 | 7-6-2/2 =0 |
AlCl3 lewis structure angle
The Structural angle directly depends upon the type of shape adopted by that intended molecule. Let us explore the angle value for AlCl3 in this section.
The value of the bond angle for AlCl3 is 1200. This is because AlCl3 has adopted a trigonal structure with no lone pairs. Hence the angle of 1200 is perfect for this shape as all the atoms have sufficient space between them and feel fewer repulsions at this angle.
AlCl3 lewis structure octet rule
The octet rule explains the stability of atoms after the bond formations. Let us look for AlCl3.
The molecule AlCl3 satisfies the octet rule in every aspect. As the octet of each molecule becomes stable ie. their respective outer orbitals get fully filled. Hence, they attain stability after bonding.
AlCl3 lewis structure lone pairs
Lone pairs are like spectators which are available along with the valence electrons but do not influence the bonding. Let us count the number of lone pairs associated with AlCl3.
The number of lone pairs for the AlCl3 structure is zero. During the bond formations, all the valence electrons are involved in the bonding phenomenon. Hence, no electron pairs are left behind to act as lone pairs.
AlCl3 valence electrons
Valence electrons are those key electrons which directly associated with the bonding. The below section give information about the valence electrons associated with AlCl3.
The total number of valence electrons for AlCl3 is 24. The number of valence electrons depends upon the electronic configurations of aluminium and chlorine atoms.
The given table explains the valence count for AlCl3.
| Atoms involved | Atomic number | Electronic configuration | Number of valence electrons in the outermost shell |
| Aluminum (Al) atom | 13 | 1s2 2s2 2p6 3s2 3p1 | 3 |
| Chlorine (Cl) atoms | 17 | 1s2 2s2 2p6 3s2 3p5 | 7 |
AlCl3 hybridization
The concept of hybridization gives the idea of the covalent bonding of the molecules. Let us see how this term is related to AlCl3.
AlCl3 has adopted the sp2 type of hybridization. The stearic number that has been observed for AlCl3 is 3 which corresponds to the sp2 category of hybridization.
The calculation for finding the stearic number for AlCl3 is given below.
- Stearic number = 1/2[V+M-C+A]
- V = Total number of valence electrons on central atom ie. 3
- M = Number of monovalent atom =3
- C = Charge on the cation = 0
- A = Charge on anion = 0
- S = ½[3 + 3] = 3
- Hence hybridization is Sp2
Is AlCl3 solid?
Solid is a state of a substance which indicates that the intended substance has a definite shape and volume. Let us find out if AlCl3 is solid or not.
AlCl3 exists in two states including the solid state. This happened because the bonds within the AlCl3 are highly influenced by the temperature and vapor pressure conditions. Furthermore, On heating, AlCl3 converted itself into a vapor state where it exists as a dimer (Al2Cl6).
Is AlCl3 soluble in water?
The solubility of any molecule is an important parameter to know if the given solute is suitable for the particular solvent. Let us see for AlCl3.
AlCl3 is soluble in the water molecule. Because when it comes in contact with water, a reaction is take place. As a result of the reaction, HCl gas is released. Hence, a thermodynamically favoured reaction is taking place as shown in the given reaction.
AlCl3 + H2O = Al(OH)3 + HCl
Is AlCl3 polar or nonpolar?
Polarity is decided by an electronegative difference, dipole moment and the symmetry of the molecule. Let us look for AlCl3.
AlCl3 is non-polar because it has a trigonal planar shape. Due to this shape, atoms are arranged symmetrically and held at an angle of 1200. The symmetrical arrangement causes the cancelling of the magnetic moment of each atom. Hence, overall dipole moment is zero.
Is AlCl3 a molecular compound?
If the given compound is formed by a covalent bond then it is considered a molecular compound. Let us find out if AlCl3 belongs to this category or not.
AlCl3 is a molecular compound. This is because aluminum atom shares its three unpaired electrons with the chlorine atoms. The bond formed within the AlCl3 molecule is covalent in nature. Hence, the mutual sharing of electrons is the basis of the covalent bonding of AlCl3.
Is AlCl3 acid or base?
Depending upon the availability of orbitals a compound can act as a base or acid. Let us observe for AlCl3.
AlCl3 is a famous lewis acid. As aluminium has a vacant valence shell which can easily accept electrons from the other species due to its electron-deficient nature. It acts as an electrophile in Friedel craft reactions and pericyclic reactions.
Is AlCl3 electrolyte?
An electrolyte generates ions when dissolve in solution. Let us see if AlCl3 is an electrolyte or not.
AlCl3 is an ideal electrolyte. This happens because it completely dissociates inside the solution and generates ions which are further responsible for the whole electrolytic activity. The conductivity value of AlCl3 is 2.3 S/m at 700. The amide-based AlCl3 is highly cost-effective and easy to make.
Is AlCl3 salt?
Salt is a substance which formed when acidic species react with basic species. The below section explains whether AlCl3 is salt or not.
AlCl3 is not considered a salt. Because it is not neutral in its action like salt and has acidic properties. AlCl3 is an inorganic compound which used as an acidic catalyst in chemical reactions whereas salt is used for buffer-based reactions.
Is AlCl3 ionic or covalent?
Ionic compounds are formed by the complete transfer of electrons while the covalent ones are by mutual sharing. Let us look for AlCl3.
AlCl3 is covalent in nature. This is because each atom shared its electrons to form bonds within the molecule. Moreover, the hybridization of AlCl3 is sp2 and only covalent molecules can formed via hybridization phenomena.
Conclusion
AlCl3 is an acidic molecular compound with sp2 hybridization and zero formal charge. It is used as a catalyst in both organic and inorganic reactions.
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Hello…Myself is Pomila Sharma. I have done my master’s in Chemistry with a specialization in synthetic organic chemistry. I have published 4 research articles. I am very passionate about the chemistry world. I believe it’s all about chemistry so let’s explore it together.
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