AlCl3 reflects both bond properties. Anhydrous aluminum chloride has covalent bond characteristics whereas aqueous aluminum chloride is an ionic bond.
There is a lot of confusion about whether AlCl3 is an ionic or a covalent bond. At the end of this article, this would no longer be a problem. I will explain everything under what condition aluminium chloride AlCl3 acts as a covalent bond and when it starts acting as an ionic bond.
As you know well, aluminum has 13 group in the periodic table and has three outermost electron and the energy required to remove an electron from an outermost shell is known as ionization energy.
- If we remove the first electron it means first ionization energy.
- Similarly, for removing the second electron we utilize second ionization energy and
- Again, for eliminating the third electron from the outermost shell the energy is named the third ionization energy.
You should remember, that this energy is calculated in joule/mole and More energy is required to remove the second electron than that of the first one. In the same case, 3rd electrons required much higher energy than second and first ionization energy.
It can be drawn as IE3>IE2>IE3
Now let’s talk about how aluminum chloride is a covalent bond and a covalent bond?
Anhydrous aluminum chloride as a covalent bond
It is to remember that to take out electrons from the outermost shell, an atom should be in a gaseous state. The sublimation process is used to turn a solid into a gas. Thereafter there is a use of ionization energy to remove electrons from the valence shell.
In case of aluminum,
On removing electron through ionization energy, it will turn into to Al3+ aluminum positive ion.
Whereas, Cl3, to put it in the gaseous state, we utilize 3/2 bond energy and then electron gain enthalpy energy. So as to turn it into 3Cl– chlorine negative ion.
When both combine, lattice energy will release and it is donated as negative -H
During the process what we have seen more energy is utilized then that of release.
We mean that,
Total energy utilized in complete process is = sublimation energy+ ( IE1+ IE2+IE3 )+ bond energy= Very high energy used.
Overall the net energy comes out to be positive. Scientifically and experimentally when energy overall value is positive, it means it represents a covalent bond. You should remember it as it is verified through various experiments. Anhydrous aluminum chloride covalent bond.
If the sum of all energy is positive then the result comes out to be a covalent bond. On seeing various examples like NaCl, magnesium chloride, we have seen the net energy is negative. So, they belong to the ionic category. Ionic and covalent are the two extreme situations.
Aqueous aluminum chloride as an ionic bond
To have an ionic compound the net sum of all the energies must be negative. This behavior is reflected by aluminum chloride only when it is in aqueous form.
Again when both aluminum and chlorine hydrated. They will form Al3+(aq) and 3cl–(aq).
During the process hydration, energy will release and also both of the elements combine release to release lattice energy.
Now remember energy is releasing from three things:
- The first is from aqueous Al 3+
- The second is from aqua chlorine 3Cl–
- Last is lattice energy when combine.
All three we will release energy and symbolize as negative energy. Again I repeat, overall net negative energy will be high than that of the positive one. This means that energy release is more than that of energy utilize.
As the net energy value is negative, Therefore, aluminum chloride AlCl3 is and ionic bond in an aqueous solution.
Overall, with the different changing circumstances AlCl3 alter its behaviour in aqua solution it starts showing its ionic character when it dehydrated it reflects covalent properties.
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