The cation H3O+ is known as the hydronium ion. If we see the nomenclature of hydronium ion, we get to know that according to the IUPAC nomenclature, hydronium ion can be referred to as oxonium.
Oxonium is a generalized name for all trivalent oxygen cations, so the use of the name hydronium is necessary to identify hydronium ions particularly.
The molar mass of the hydronium ion is 19.02 g/mol.
The production of this ion is during the protonation of water;
H2O (Water) + H+ (Hydrogen ion) —–> H3O+
This ion is used in determining the pH of water. As water dissociates into OH- and H3O+ and we can check the pH of the water using a particular process.
The hydronium ion is used in various reactions and the production of different compounds. Both organic and inorganic chemistry includes hydronium ion to a large extent.
But before reading the use of this ion in different reactions, we must have knowledge about the basics of this ion, like, lewis structure, geometry, etc.
Knowing these basics will deepen our knowledge about this ion more. We should always try to know the background of any compound before studying any reaction regarding it.
So let’s dig deep and know about some interesting information about hydronium ion!
H3O+ Lewis Structure
Let’s try to draw the lewis structure of H3O+.
First of all, we need to calculate the total number of valence electrons present in hydronium ion.
Hydrogen = 1
3*Hydrogen = 3
Oxygen = 6
Total = 9
Now the important point is, not to forget about the + sign. + sign indicates losing an electron from the total valence electrons.
( – sign indicates gaining an electron)
Thus, the total valence electron is 8 now.
Secondly, we need to determine a central atom which is generally the atom with the most available sites for bonding. In this case, Oxygen is the central atom.
Next, we need to draw a skeletal structure of H3O+ with single bonds only. After that, to complete the lewis structure of H3O+ we have to fill up the octet of atoms with the remaining electrons.
At the end of drawing the lewis structure of H3O+, we should check that, all the atoms are having their lowest possible formal charge.
The attached image below shows the lewis structure of hydronium ion;
How to draw Lewis Structure
A lewis structure helps us to find out about the structure of the compound, types, and the number of bonds, physical properties, and how the compound interacts with other compounds.
Drawing a lewis structure is pretty simple!
There is a common way by which we can draw the lewis structure of any compound. To simplify the process more for you, I have jotted down the steps below in bullets :
- Calculate the total number of valence electrons in the molecule. Do take care of +, – signs while calculating.
- Choose a central atom; generally the atom with the highest bonding sites.
- Draw a skeletal structure with single bonds only.
- Fillup the octet of the atoms with the remaining electrons. Keep in mind to start with the electronegative atoms and proceed to the electropositive one.
- Give multiple bonds if required for fulfilling the octet of the atoms.
- At last, make sure all the atoms are having their lowest possible formal charge. You can calculate the same with the formula given below:-
Lewis structure rules are almost the same for all molecules, although some exceptions exist here as well. Chemistry is all about exceptions after all !!
The hybridization of H3O+ (hydronium ion) is Sp3.
The hybridization of any molecule can be found using a formula.
H = ½ [ V+M-C+A]
V= No. of valence electrons
M= no. of monovalent atom
C= charge of the cation
A= charge of the anion
If, H= 2 = Sp hybridization
H= 3 = Sp2 hybridization
H= 4 = Sp3 hybridization
H= 5 = Sp3d hybridization
H= 6 = Sp3d2 hybridization
Now let’s find the hybridization of H3O+ using this formula,
In hydronium ion, the central atom is oxygen and it has 6 valence electrons.
Thus by the formula, V = 6
3 hydrogen atoms are bonded to oxygen, so the number of the monovalent atoms (M) = 3
As this is a cationic molecule thus, C = 1
So, H = ½ [ 6 + 3 – 1] = 4
Thus we can say hybridization of H3O+ is Sp3.
Hybridization is generally the mixing of atomic orbitals to form a new hybrid orbital.
We can determine the hybridization of a molecule from the VSEPR chart as well, which we will discuss in the next part.
H3O+ Molecular Geometry
The molecular shape of H3O+ is a trigonal pyramid and electronic geometry is tetrahedral.
From the above chart, we can see that hydronium ion is a AX3E type molecule
(A= central atom, X= bonded atom, E= lone pair on A).
So according to the VSEPR chart, H3O+ has trigonal pyramid as its molecular shape and tetrahedral as its electron geometry.
The image attached below explains all the above-mentioned concept,
Now there is a clear difference between molecular shape and electronic geometry.
In a molecular shape, only the atoms are taken into consideration while determining the structure of the molecule.
But in electron geometry, all electron pairs are taken into consideration.
In other words, lone pairs are taken into consideration in the case of electron geometry and not in molecular shape.
From the VSEPR chart, hybridization can also be determined as I stated earlier. And we can see from here as well that hydronium ion has Sp3 hybridization.
The reason for the polarity also emerges due to the presence of lone pair on the oxygen atom in the H3O+ molecule.
The net dipole comes out to be some non-zero value that makes H3O+ a polar molecule.
H3O+ Molecular Orbital (MO) Diagram
A molecular orbital diagram of any molecule gives us an idea about the mixing of orbitals in the molecule.
Talking about the overlap diagram of H3O+, it is almost similar to H2O but with one electron less and one hydrogen more.
Given below is the image of the molecular orbital diagram of H3O+ and also that of H2O for reference.
In the above image, On the left-hand side, the MO diagram of hydronium ion is explained.
The MO consists of the atomic orbitals of 3 hydrogens. Moreover, the atomic orbital of O+ has one electron less than that in water.
Together they make the MO of the molecule with 2 electrons in the non-bonding orbital.
Also, the bonding orbital is fulfilled with 6 electrons and antibonding is empty.
The image also contains the MO diagram of OH- for reference.
From the molecular orbital diagram, we can see that only sigma bonding is happening in hydronium ion, this indicates that only head-on overlap is possible in this ion.
This is the explanation of the molecular orbital diagram of hydronium ion.
A MO diagram helps us to find the bonding order of a compound which in result gives us information like bond length, the stability of the compound.
This article revolves around the structure, bonding, and hybridization of hydronium ions. The molecular orbital diagram is explained as well.
There are several uses of hydronium ion as I explained earlier. Learning the basics will help you to understand the reactions more and have a clear picture of the hydronium ion. After this, you can easily understand all other things related to hydronium ions.
I hope the article was helpful in some way or the other and hope you gained some knowledge at the end!
If there is any query, feel free to ask me and have a happy reading!