Al2O3 Lewis Structure & Characteristics: 17 Complete Facts


Valence electrons of atoms get represented in the form of lines and dots called Lewis structure. Let us have a brief discussion on the Al2O3 Lewis structure below.

Al2O3 contains two elements i.e. aluminum metal and oxygen atoms. It is the combination of metal and non–metal compounds. Thus it forms an ionic compound. Al2O3 is composed of 2 aluminum metals and 3 oxygen atoms. Both Al atoms lost their 3 valence electrons to 3 O atoms thus it has a +3 charge.

The 3 O atoms gain 2 electrons from 2 Al atoms thus it has a -2 charge on it. It has an ionic bond between all Al and O atoms of Al2O3. The 2 Al and 3 O atoms get placed in a square bracket due to the presence of charge on it. Let us discuss lone pairs, formal charge, the octet rule, and the shape of the Al2O3 lewis structure with various characteristics and facts.

How to draw the Al2O3 Lewis structure?

It has some steps or rules to draw the Lewis structure of any chemical compound which are given below.

Valence electrons and bonds in Al2O3:

Evaluate the overall valence electrons available on the Al2O3 lewis structure by adding the valence electrons of each Al and O atom. There is an ionic bonding within the Al2O3 lewis structure due to sharing of electrons.

Lone pair electrons and octet rule on Al2O3:

After bonding calculates the lone pair electrons on the Al2O3 lewis structure. Apply the octet rule on each Al and O atom of the Al2O3 lewis structure to check whether it has complete or incomplete octets.

Formal charge and geometry and shape of Al2O3:

Evaluate the formal charge present on the Al and O atoms of the Al2O3 lewis structure by using a given formula. Also identify the shape, geometry, hybridization, and bond angle of the Al2O3 molecule.

Al2O3 lewis structure

Al2O3 valence electrons

The number of outermost shell electrons available on an atom or element is known as valence electrons. Take a brief look at the Al2O3 valence electrons given below.

Al2O3 lewis structure has overall 24 valence electrons present on it. The aluminum metal belongs to the 13th periodic table group. The oxygen atom belongs to the 16th periodic table group. Thus the Aluminium and Oxygen atom has 3 and 6 valence electrons in their outermost shell orbital respectively.

The steps for the valence electron calculation for the Al2O3 lewis structure are given below.

  • Valence electrons on aluminium atom is = 3 x 2 (Al) = 6
  • Valence electrons on oxygen atoms is = 6 x 3 (O) = 18
  • Valence electrons on Al2O3 lewis structure is = 6 + 18 = 24
  • To know the total electron pair on the Al2O3 lewis structure we have to divide valence electrons by 2 = 24 / 2 = 12
  • Therefore the Al2O3 lewis structure contains 24 valence electrons and 12 electron pairs.

Al2O3 lewis structure lone pairs

Unshared pair of electrons or non–bonding electrons on an atom or molecule is called the lone pair of electrons. Below is the description of Al2O3 lone pair electrons.

Al2O3 lewis structure has a total of 6 lone pair electrons. It has 24 total valence electrons in Al2O3. 12 electrons are being bond pairs forming 2 single covalent bonds and 2 double bonds within Al and O atoms. Leftover 12 electrons are placed on 3 O atoms as unshared electrons i.e. lone pair electrons.

Below is the explanation for the calculative part of Al2O3 lewis structure lone pair electrons.

  • Lone pair electrons on Al2O3 = Valence electrons of Al2O3 – number of bonds / 2
  • Lone pair electrons of central O atom = 6 ( V. E) – 2 (Al – O bonds) / 2 = 2
  • Lone pair electrons on outer O atoms = 6 ( V. E ) – 2 (Al = O bonds) / 2 = 2
  • Lone pair electrons on all 3 O atoms = 2 (L. P on central O) + 2 x 2 ( L.P on outer O) = 2 + 4 = 6
  • Hence, each O atom has 2 lone pair electrons in the Al2O3 lewis structure.
  • Therefore, the Al2O3 lewis structure has 6 total lone pair electrons.

Al2O3 lewis structure octet rule

The presence of 8 electrons in the outermost orbit of an atom is considered a stable atom tells in the octet rule. Let us discuss the application of the octet rule on Al2O3.

Al2O3 lewis structure has complete octets of all three oxygen atoms. Rather both the aluminum atoms have empty orbital due to the donation of their three electrons. The two Al atoms have 3 valence electrons. All these 3 electrons of 2 Al get donated to 3 O atoms. Thus it has a +3 charge on it.

The three O atoms gain 2 electrons each from 2 Al atoms and have a -2 charge on each O atom. Thus each O atom gets surrounded by 8 electrons and has a complete octet.

Al2O3 lewis structure formal charge

The positive or negative charge on the atoms or molecules due to the loss or gain of electrons is called a formal charge. Below is the Al2O3 formal charge calculation part.

The formal charge of Al2O3 lewis structure is = (valence electrons – non-bonding electrons – ½ bonding electrons)

The given below table shows the detailed calculation for the Al2O3 lewis structure.

Atoms of Al2O3
lewis structure
Valence
electrons
on Al,
and O
Non–bonding
electrons on
Al, and O
Bonding
electrons on
Al, and O
The formal
charge on Al,
and O
Two Aluminium
(Al) atoms
030000( 3 – 0 – 0 / 2 )
= + 3  
Three oxygen
(O) atoms
060800( 6 – 8 – 0 / 2 )
= – 2
Al2O3 lewis structure formal charge, Al = + 3, O = – 2.

Al2O3 lewis structure shape

The specific arrangement of atoms in a molecule forming a geometrical shape is called molecular shape. Let us discuss some brief about the Al2O3 shape.

The Al2O3 lewis structure has a trigonal planar shape and geometry. The Al2O3 compound has 2 central atoms i.e. Al atom. Both these 2 central Al atoms do not have lone pair electrons and are attached with 2 bonded O atoms. So, it has an AX3 generic formula of VSEPR theory and has a trigonal planar shape.

Al2O3 hybridization

The atom undergoes the mixing and recasting of atomic orbitals to form a new hybrid orbital with the same energy is called hybridization. Let us discuss Al2O3 hybridization.

The Al2O3 lewis structure has ‘sp2’ hybridized two central Al atoms. The aluminum atom has a steric number 3. Al atom steric number is calculated as = number of bonds on Al + lone pairs on Al i.e. 3 + 0 = 3. Thus, as per VSEPR theory, Al of Al2O3 has steric number 3 so it is ‘sp2’ hybridized.

In the Al2O3 molecule, there is mixing or overlapping of atomic orbitals of the central Al atom. There, one ’s’ and two ‘p’ orbitals of the central Al atom get mixed together and form a new ‘sp2’ hybrid orbital with the same energy as previous orbitals.

Al2O3 lewis structure angle

The angle within all the immediate bonds of a molecule is called the bond angle of that molecule. Take a brief look at the Al2O3 lewis structure bond angle.

Al2O3 compound has a 120-degree bond angle. It has an Al central atom connected with two O atoms forming an ionic bond due to the loss of all 3 electrons.  Thus it has an O – Al – O bond angle of 120 degrees within them.

Is Al2O3 solid?

Solid compounds are having closed packing of their atoms and have a specific crystal form of arrangement and hard nature. Let us discuss whether Al2O3 is solid or not.

Al2O3 is a solid crystalline compound. It is a white or colorless compound with no odor. It shows a repeating regular pattern of a hexagon formed within Al3+ and O2- ions. Thus the particle in Al2O3 has the crystal structure of hexagonal closed packing (HCP) of Al3+ and O2- ions.

Why Al2O3 is a solid?

Al2O3 is solid because of its hexagonal closed packing structure of ions. The bigger-sized O2- ions occupy octahedral voids and smaller-sized Al3+ ions occupy tetrahedral voids forming a 6 layers pattern in HCP. The Al3+ ions are placed centrally and surrounded by 6 O2- ions in a hexagon.

It forms alternate layers of both Al3+ and O2- ions. The middle layer of Al3+ions has triangular-shaped grooves between 2 O2- layers. In HCP the ions occupy 74% of space and 26% of space is empty.  It has 12 coordination numbers and 6 atoms in each unit cell of the hexagon. It is known as corundum.

Is Al2O3 soluble in water?

The solubility of a compound depends upon its ability to dissolve of that in water or other solvents. Below is a deep description of the solubility of Al2O3 in water.

Al2O3 is insoluble in water. Al2O3 is an ionic compound. But it has strongly bonded or closed-packed ions in its molecules. It cannot get further ionized into the water to form hydrogen bonds. So, there is no formation of hydrogen bonds within opposite ions of Al2O3 and water and has insoluble nature.

Why Al2O3 is insoluble in water?

Al2O3 is insoluble in water because it has a complex hexagonal closed-packed crystal structure. It has lattice energy higher than hydration energy. The O2- ions of Al2O3 are very strongly held with each other in the HCP crystal lattice. Thus it cannot react with water and has insoluble nature.

Is Al2O3 polar or nonpolar?

The polarity of a compound is determined by different electronegativities of its atoms showing polar or non–polar bonds. Let us discuss the polar/non-polar nature of Al2O3.

Al2O3 is a polar compound. There are a big electronegativity difference between it Al and O atoms. The electronegativity of the Al atom is 1.61 and the O atom is 3.44. Thus it has 2.34 electronegativity differences which are more than 0.5 to 1.8 values given by Puling’s rule. So, it has polar nature.

Why Al2O3 is a polar compound?

Al2O3 is polar due to the creation of dipoles in the molecule. The Al atom is less electronegative than the O atom. So, electron density attracts toward more electronegative O atom. A partial positive charge on Al and partial negative charge on O atoms i.e. generates dipoles and shows polar nature.

Is Al2O3 a molecular compound?

Molecular compounds are compounds in which the atoms get attached with strong covalent bonds. Take a look at the discussion on whether Al2O3 is molecular or not.

Al2O3 is not a molecular compound. Rather it is an ionic compound. There is no presence of any strong covalent bonds within the Al2O3 molecule. It has strong ionic bonds with Al3+ and O2- ions. Also, the Al and O atoms have positive and negative charges due to electron exchange.

Is Al2O3 acid or base?

The compounds that have characteristics of a proton donor are acids and a proton acceptor is a base. Below is a brief discussion on whether Al2O3 is an acid or a base.

Al2O3 can act both as an acid or base. Al2O3 is an amphoteric compound. Basically, it is an amphoteric oxide containing oxide ions. It has a combination of both metals and non-metals. Al2O3 on reaction with acid act as a base and on reaction with a base, it works as an acid.

Why Al2O3 is amphoteric?

Al2O3 is amphoteric because in a reaction with acid like HCl it acts as a base and produces salt AlCl3 and water. It reacts with a base like NaOH it acts as a base to form a complex sodium tetrahydroxoaluminate. The O2- ions lose or gain electrons to form covalent bonds to act as acid and base.

Al2O3 + 6 HCl → 2 AlCl3 + 3 H2O (Al2O3 base)

Al2O3 + 2 NaOH + 3 H2O → 2 NaAl(OH)4 (Al2O3 acid)

Is Al2O3 electrolyte?

Electrolytes are the species that can get ionized and are able to conduct electricity due to ions’ movement. Let us have some discussion on whether Al2O3electrolyte or not.

Al2O3 is an electrolyte. It is consists of metal and non–metal species and ionic in nature. It cannot react with water molecules to dissociate into it. It can itself get ionized as Al3+ and O2- ion on the application of external energy like heat. Hence, due to ionization, it can act as an electrolyte.

How Al2O3 is an electrolyte?

Al2O3 is an electrolyte because it can get dissociate as Al3+ and O2- on heating. They can move freely and conduct electricity. On electrolysis, Al3+ ions go towards the cathode due to the reduction reaction. O2- ions go towards the anode due to an oxidation reaction.

The oxidation-reduction reactions and net overall reaction for electrolysis of Al2O3 are given below.

4 Al3+ + 12 e → 4 Al (Al metal at (-) cathode) / Reduction.
6 O2- – 12 e → 3 O2 (O2 gas at (+) anode) / Oxidation.
2 Al2O3(l)  → 4 Al(l)  + 3 O2(g)

Is Al2O3salt?

Salts are the compounds which is the outcome of the reaction between acid and base compounds. Let us have some discussion on whether Al2O3 is salt or not.

Al2O3 does not act as salt. It cannot produce with the acid-base reaction. Al2O3 is produced due to the reaction between aluminum metal with oxygen gas (atmospheric O2). Thus, aluminum metal overall covered with aluminum oxide layer from which we get Al2O3. So, it cannot show behavior of a salt.

4 Al + 3 O2 → 2 Al2O3

2 Al(OH)3 → Al2O3 + 3 H2O

Is Al2O3 ionic or covalent?

Ionic compounds are bonded with an electrostatic force of attraction. Covalent compounds have strong covalent bonds. Below is a brief on whether Al2O3 is ionic or covalent.

Al2O3 is an ionic compound. It is formed by combining metal (Al) and non–metal (O) atoms. The compounds with metal and non–metal species are ionic in nature. It has positive and negative charges due to the exchange of electrons on it. It can ionize as Al3+ and O2- ions and shows an ionic nature.

Why Al2O3 is ionic?

Al2O3 is ionic because the Al3+ and O2- ions are held together with the electrostatic force of attraction forming a strong ionic bond. On heating, it further dissociates as positive and negative ions. It has an electronegativity difference of 2.34 between Al and O atoms forming ionic Al2O3.

Conclusion:

Al2O3 lewis structure has 24 valence electrons, 6 lone pair electrons, and complete octets of all O atoms. It has a formal charge of +3 on Al and -2 on O atom. It has a trigonal pyramidal shape with a hexagonal closed-packed crystal lattice structure. It has sp2 hybridization and a 1200 bond angle. It is a solid polar ionic compound and is water-insoluble.

Dr. Shruti Ramteke

Hello everyone I am Dr. Shruti M Ramteke, i did my Ph.D in chemistry. I have five years of teaching experience for 11-12 standard, B,Sc and MSc in chemistry subject. I have published total five research articles during Ph.D on my research work and i have fellowship from UGC for my Ph.D. My Masters with specilization Inorganic chemistry and my graduation with chemistry, zoology and environmental science subjects. thank You

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