Perchlorate ion or [ClO4]- is one of the most abundantly found ions in salts. Do you know that you can find the presence of ClO4 even on Mars?
From food packaging to acting as oxidizers in propellants for rockets, it has quite a varied range of useful properties.
However, its exposure to drinking water and edible vegetables can be harmful to the human body and can cause severe unwanted effects.
Perchlorate ion has a molar mass of 99.45 g/mol and usually forms salts with the likes of sodium, ammonium, potassium. It is usually in colorless solid form although it can also form acid ( perchloric acid).
Let us now have a quick and detailed look into the nature of the chemical bonding of ClO4.
Lewis Structure of ClO4
Chemical bonding is one of the most important and interesting chapters of chemistry.
How some atoms come together and form covalent bonds with each other inside a molecule is something we need to visualize to be able to grasp the science behind this.
Lewis Structure or electron-dot structure is one such representation of chemical bonding between atoms inside a compound which helps us sketch a line dot diagram of atoms along with electrons and bonds.
Let us check how we can perfectly form a Lewis Structure diagram of any molecule with the help of the following steps:
The very first step of the above-mentioned process is to list down the total number of valence electrons that the molecule contains.
Valence electrons refer to the number of electrons that atoms have in their outermost shells.
Now, there are two signs or symbols that we have to work with while finding out the Lewis Structure: ‘+’ and ‘-’.
[ ‘+’ during a loss of electrons i.e increase of positive charge & ‘-’ during gain of negatively charged electrons]
We are done with calculating the total number of valence electrons of all the atoms in a given molecule. Our second step will be to determine which one of the constituent atoms will act as the central atom.
We can easily find out the central atom if we have a clear understanding of the electronegativity concept. The atom having the highest number of binding sites is the central atom.
Identifying the central atom makes our task a lot easier, doesn’t it?
Now, we have to sketch a skeleton diagram of the molecule along with atoms and their valence electrons along with any single bonds happening between the atoms.
The octet rule is a significant concept that lets atoms try to reach their closest noble gas configurations. Leaving aside hydrogen that tries to reach helium configuration and hence needs only two electrons in its outermost shell, all other atoms tend towards eight valencies.
This is known as octet configuration. In this step, we will focus on atoms to have eight electrons in their outermost shells starting with the more electropositive ones.
Now that we have found out the octet configurations, we will focus on multiple bond formation in the penultimate step.
If there is any tendency of an atom to form double or triple bonds, we can show them via double or triple straight lines inside the Lewis Structure diagram.
Do you know that sometimes we can end up having more than one Lewis Structure sketch for a single molecule? This can be quite confusing.
In order to have a unique LS for every different molecule, we have to depend on the formal charge. This charge
helps create a perfect Lewis Structure by sharing bonding electrons equally among the bonded atoms.
In this final step, therefore, all we need to do is calculate the formal charge.
The formula in the above diagram helps us find out the formal charge easily.
Now, let us focus on our given molecule ClO4.
At the very beginning, calculate the valency:
Chlorine is a halogen, hence it belongs to the halogen family of group 7. It, therefore, has 7 valence electrons.
Oxygen, on the other hand, belongs to the chalcogen family of group 6, therefore having 6 electrons in its valence shell.
Total number of valence electrons in ClO4 = 7*1 + 6*4 = 31
But as we know ClO4 is an ion having a negative charge of -1.
So, total electrons = 32.
Chlorine is the least electronegative atom here, hence, it will be considered as the central atom.
Let us now draw the skeleton diagram.
After drawing the skeletal sketch and making the valence electrons 32 with 8 around each, we seem to have completed the dot structure. But here, comes an exception.
This is not yet done. We have to check the formal charge.
As per the formula mentioned above, we find out that chlorine has a formal charge of +3 whereas each oxygen has a formal charge of -1.
The total formal charge= +3 +(-1)*3 = -1.
To make the formal charge near to zero value, we will form three double bonds around Chlorine each one with an Oxygen atom.
This makes three oxygen atoms doubly bonded with chlorine while one remains single-bonded. The negative charge on [ClO4]-1 is due to the single-bonded oxygen.
Thus, we have completed our Lewis Structure diagrammatic representation of perchlorate ions.
ClO4 Molecular Geometry
Only understanding the two-dimensional structure of a molecule is not enough for detailed knowledge of the characteristics and nature of a molecule.
Lewis Structure does give us a viewpoint on the nature of bonds and formal charge concepts but it has its drawbacks.
To have a clearer idea of a given molecule, we need to also have in-depth knowledge about the 3-dimensional nature.
This is known as molecular geometry which tells us about the molecular shape.
Now, how can you determine the molecular geometry of the ClO4 ion?
Well, the most widely used model is the VSEPR model or Valence Shell Electron Pair Repulsion Theory model. This is an extension of the LS concept where we come across newer terminologies like the steric number and electron repulsion (minimum repulsion between valence electron pairs is supported by chemical nature).
Now, for [ClO4]-, we already have found out that chlorine is the central atom. If we look closely into the lewis structure, we can see that all the valence electrons around chlorine are bonded with oxygen in either single or double bonds( in this case 1 single and 3 double bonds).
So, the number of lone pairs of Chlorine here is 0.
The new term steric number, if you are already aware of, basically is the coordination number, hence the value here is 4 for central Cl.
Therefore, as per the VSEPR model, we get to see that the molecular shape of the perchlorate ion is tetrahedral with each bond angle around 109 degrees.
So, what is hybridization?
Hybridization is one of the most crucial theories of chemical bonding. If we know the Lewis Structure and Molecular geometry, it is just another step before we also get to learn about hybridization.
Elements and compounds exhibit a wide range of unique characteristics. You do know the fact that an element can showcase different properties while reacting with different or sometimes the same element, don’t you?
Well, hybridization has a huge role to play in this.
The atomic orbitals mix to form hybridized orbitals that possess different energies and other features.
Chlorine has an atomic number of 17. Its electronic configuration is: [Ne]3s23p5.
The central chlorine atom has a sigma bond with an oxygen atom. And, it has three double bonds i.e. one sigma and one pi for each double bond.
Hybridization can be calculated by a simple formula:
Here, H=hybridization value
V= valence electrons
M= monovalent atom
Here, V=7( according to central chlorine)
Now, H=0.5(7+1) = 4.
Therefore hybridization of ClO4 is sp3.
Note: Remember, while we calculate hybridization we take into account the hybrid orbitals that are linked to lone electron pairs and sigma bonds. We do not care about the pi bonds.
Polarity and dipole moment are some of the important terms that we need to consider while referring to the chemical bonding of a molecule.
The chemical bonding nature determines whether a molecule is going to be polar or non-polar. This depends on the distribution of positive and negative charges and occurs due to a difference in electronegativity between the constituent atoms.
This can be measured by dipole moment – net dipole moment when zero, a molecule is called non-polar.
D = Q * R
D denotes the dipole moment of the molecule, Q represents the charge on atoms, and R represents the distance between the centers of both atoms.
Do you know that perchlorate ion is non-polar?
This may come as a surprise due to the presence of the anionic charge. Although ClO2- is polar, ClO4- is non-polar.
ClO4 ion is non-polar in nature.
Since oxygen has a higher electronegativity value than chlorine, the Cl and O bonds are polar in nature. But the equal strength of the four bonds formed inside the molecule giving rise to four resonance tetrahedral structures results in a net-zero dipole moment and thus perchlorate turns out to be non-polar in nature.
In this article, we have covered in details, the Lewis Structure, Molecular Geometry, Hybridization, and Polarity of perchlorate ion i.e. [ClO4]-.
This has been an extensive discussion and we hope that by now you have got a clear idea about the bonding nature and internal properties of the anion.