Is AlCl3 an ionic or a covalent compound?

Let’s look at the properties of aluminium chloride, an antiperspirant. Aluminum trichloride is another name for aluminium chloride.

AlCl3(H2O)n (n = 0 or 6) is the formula for this chemical. It has a 133.34 molecular weight. Anhydrous aluminium chloride is a pungent-smelling white to grey powder.

When combined with iron chloride, the product takes on a yellow tint rather than the pure white colour.

As a Lewis base, anhydrous aluminium trichloride is employed in a variety of chemical applications. The solution of aluminium chloride seems to be a straw-colored liquid.

It has a higher density than water. It can also be present in over-the-counter antiperspirants and prescription anti-bleeding medications.

Irritation of the skin, eyes, and mucous membranes is possible. If ingested, it could be harmful.

Let’s look at the facts to see if it’s an ionic or a covalent compound.

Is aluminium chloride an ionic or a covalent compound? A covalent compound is aluminium chloride. Al3+ is highly charged in nature and has the ability to significantly polarise the electron clouds of Cl. As a result, the electrons are shared between the two ions. It is thus a polar covalent molecule.

Let’s take a closer look at the causes.

The Covalent Nature of AlCl3: An Explanation

Aluminum chloride’s covalent nature is justified for the three reasons listed below.

Reason 1: Because Al’s ionisation energy is so high, chlorine has a hard time removing electrons from its outer shell.

As a result, rather than losing three electrons, Al shares them with three Cl ions. A covalent bond is established when electrons are shared between two atoms.

Explanation: In an ionic bond, two atoms do not share all of the electrons. Instead, they are passed from one atom to the next.

The charge’s magnitude is determined by the number of electrons transported.

Aluminum has a rather large positive charge due to its +3 charge. The electron cloud of the other ion that has taken electrons from either aluminium (or other) or any other positive ion is then attracted by this positive charge.

The difference can be seen by comparing these two examples.

Although the bonds in aluminium chloride are ionic, they do have a higher covalent nature.

Aluminum has a charge of +3. The positive ions pull the electron cloud of the chlorine atom when it interacts with it.

When it comes to the size of a chlorine atom, it is quite little.

As a result, the electrons in the outer shell are well protected from nuclear charge.

Aluminum has a large positive charge, which pulls on the chlorine electron cloud. The chorine electron cloud will be drawn closer to the aluminium as a result.

In this case, the positive charge of the aluminium cation cancels out the negative charge of the electron cloud.

With the covalent character, it forms an ionic bond.

Reason 2: The bond will be covalent if the anion is big.

To further illustrate, while comparing AlF3 with AlCl3, the F ion is smaller than the Cl ion. As a result, AlCl3 forms a covalent link, whereas AlF3 forms an ionic bond.

Explanation: The electron transmission between the metal and the non-metal in AlCl3 is incomplete. Rather, the electrons are shared between the two atoms.

The three electrons in Al’s valence shell are grouped in concentric electron shells surrounding each of the three Cl atoms, allowing the outer shell to achieve a stable electronic configuration of eight electrons.

Al3+ has a high charge density because it is a tiny, highly charged cation.

Because the ionic bond between chlorine and the hard cation is relatively broad and has a low charge density, it has a considerable covalent character. Aluminum ions can easily polarise it.

Similarly, the Cl atoms receive one electron from the Al atoms in order to establish their stable electron configuration.

As a result, AlCl3 is a compound made up of one Aluminum atom and three Chlorine atoms.

Reason 3: A covalent bond is formed when the difference between the electronegativities of two joined atoms is smaller than 1.7.

The difference in electronegativity between chlorine and aluminium is 1.55, indicating that the AlCl3 link is covalent.


The electronegativities of chlorine and aluminium differ, indicating the strength of their electron density in relation to one another.

Fluorine (because to its severe electronegative nature) will strip electrons from aluminium, resulting in ionic rather than covalent connections.

However, due to its minimal electronegativity difference, AlCl3 is covalent.

Why is AlCl3 Hydrous Ionic?

The hydration energy of the resultant ion should be higher than the ionisation energy of the original bond for any covalent bond to become an ionic bond.

AlCl3 is a covalent compound. Because the 3rd ionisation enthalpy of Al is high, it takes a lot of energy to convert an Al to an Al3+. Hydrated AlCl3 is ionic.

Al(g) + 5114 kJ/mol → Al3+(g) + 3e+

As a result, we can conclude that it enjoys forming covalent connections with Cl atoms.

It is noticed, however, when AlCl3 is exposed to a hydration process that releases a large amount of energy dissolved in water.

AlCl3   +   H2   —->   AlCl3.6H2O    +    E

The letter E stands for energy. The same amount of energy is required to lift 3e off the Al atom.

It is clear that Al does not survive as Al3+ in this circumstance. Instead, it takes the following forms:

[Al(H2O)6]+ [Al(H2O)6]+ + Cl+.

This implies that the Hexa – hydrated aluminium chloride is ionic.

Because of the strong polarisation feature of Al+3, the anhydrous AlCl3 is covalent in nature. When AlCl3 is hydrated, it exhibits the following reaction.

AlCl3 + 6H2O → [Al(H2O)6]+ + 3Cl−

The hydration energy of the Al3+ is greater than its ionisation energy, hence AlCl3.6H20 is ionic in nature.

What is the definition of a covalent compound?

Bonds between atoms where electrons are shared define covalent substances.

Because they share electrons equally, covalent compounds have different physical features than ionic ones, such as lower electrical conductivity and dizzier melting temperatures.

The division of electrons between two or more atoms distinguishes covalent bonds.

These bonds are more commonly found in nonmetals or between elements that are similar.

Two atoms with similar electronegativity will not exchange an electron from their outermost shell; instead, they will share electrons to fill their valence electron shells.

Methane (CH4), iodine monobromide (IBr), and carbon monoxide are examples of compounds with just covalent connections (CO).

See my essay on the covalent nature of CH4 for more information.

What are Ionic Compounds and How Do They Work?

Electrostatic force is the force that produces ionic bonding.

The attraction between opposing charges causes the electrostatic force.

On each side of the bond, a positive charge (the cation) and a negative charge (an anion) are present when the more electronegative atom gives up one or more electrons to the less electronegative element.

Positive and negative charges attract each other and form a strong relationship.

Ionic bonding develop between metals and non-metals as well. Non-metal can receive electrons and vice versa.

Metals typically lose an electron to a non-metal to form a stable combination. An ionic bond can be formed by transferring more than one electron.

Sodium chloride, also known as table salt, is an ionic compound. In comparison to chlorine, sodium is more electronegative.

As a result, sodium gains a positive charge and loses one electron.

As a result of gaining an electron, chlorine develops a negative charge.

As a result of this strong attraction force, these two oppositely charged atoms get linked.

KI and MgCl2 are two more chemicals that exhibit ionic bonding.

You can also read about MgCl2’s ionic nature in this article.

AlC3’s properties

Physical characteristics

  1. Aluminum chloride has a melting and boiling point that is exceedingly low.
  2. It might be sublimed at 180 degrees Celsius.
  3. In a molten form, it is a poor conductor of electricity.
  4. Aluminum chloride is white in colour. It is, however, frequently tainted with iron trichloride. This causes it to turn yellow.
  5. It could melt at pressures more than 2.5 atm and temperatures greater than 190°C.

Chemical characteristics

  1. Aluminum chloride is a Lewis acid that is very powerful.
  2. It serves as a major industrial catalyst.
  3. When AlCl3 comes into touch with water, it reacts violently.

Aluminum Chloride has a variety of uses.

  1. Aluminum chloride (AlCl3) is a catalyst that is employed in a variety of chemical processes.
  2. It is widely employed in Friedel-Crafts reactions, both in acylations and alkylations.

It’s used to make anthraquinone from phosgene and benzene, among other things.

  1. Aldehyde groups are attached to aromatic rings using aluminium chloride.


A covalent compound is aluminium chloride. The following examples demonstrate this:

Aluminum, for example, has a high charge density.

  1. The chloride’s electron cloud can be polarised.
  2. The two positive aluminium ions and the negative chloride ion share electrons as a result of the preceding two reasons.

AlCl3 is thus a covalent character.

Read more: Geometry, Hybridization, and Polarity of SeO2 Lewis Structure

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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