Sulfate ion (SO42-) is one of the most common ions that people in chemistry need to deal with. This is a polyatomic anion having a negative charge of -2.
We find sulfates in a wide range of compounds, some of the well-known being MgSO4, CaSO4, Na2SO4, and PbSO4. We can easily prepare sulfates via oxidizing metal sulfites and sulfides. We can also use sulfuric acid and metals to get our desired sulfate salts.
Zn + H2SO4 ——> H2 + ZnSO4 ( Here we get zinc sulfate by treating zinc metal with sulfuric acid.)
Since we can easily get hold of this ion, be it naturally or synthetically, this helps us in our daily lives in a lot more ways than you can think of right now!
From body and hygiene-care products like toothpaste, shampoos, soaps, and detergents to water treatment procedures, we can find the application of sulfate compounds everywhere.
Although it can be used in several facilities, sulfates have their drawbacks as well.
It plays an important factor in acid rain composition. Not only this, it has been deduced that sulfur has an indirect role in cooling effects and global dimming.
We must learn about the chemical bonding and additional features ofSO42- so that we have a clearer image and idea about nature and atomic reactions.
SO42 Lewis Structure
As per the internal structure of a molecule, we know that a molecule is composed of atoms which in turn is composed of a nucleus and electrons.
The electrons, which are negatively charged particles, are present in shells surrounding the atomic nuclei.
When we discuss chemical bonding through the Lewis Structure concept, we consider the electrons of the outermost shell i.e. valence shell electrons to be dots and the bonds formed between atoms as straight lines.
The Lewis Structure is therefore also known as electron dot structure and is one of the most predominant and simplest concepts to understand the chemical bonding of molecular compounds.
Here, we will work with sulfate ion i.e SO42-.
Step 1: Count the total number of valence electrons present in the molecule/ion
For sulfate ions, we have one molecule of sulfur and four molecules of oxygen.
Sulfur and oxygen both belong to the same group in the periodic table( the chalcogen family) and have six valence electrons each.
total valence electrons in SO42- = 6*1 + 6*4 +2 = 32
Note: We had to add two electrons due to the negative 2- charge on sulfate ion.
Step 2: Find out the central atom
To find out the central atom of the molecule, we have to consider electronegativity.
Electronegativity is the measurement of an atom’s tendency to attract negatively charged electrons to form anionic molecules.
Here, between sulfur and oxygen, oxygen is more electronegative. Therefore, S or sulfur is the central atom.
Step 3: Draw the skeleton diagram of the molecule
We are now going to sketch the skeletal diagram of sulfate ion with the help of atomic symbols and dot line structures.
Here, we have put the symbols of sulfur and oxygen as per notations and put the valence electrons as dots.
Step 4: Check the Octet rule
Atoms present in the main groups of the periodic table tend to have a valency of eight following noble gases like argon, xenon, and so on.
So, when atoms of different types come to combine in a molecular form, they follow the octet rule.
As we see in the above-mentioned diagram, the five molecules have fulfilled their octet configuration and the total valence electron number remains 32. By drawing single bonds, we get the structure as:
Step 5: Formal Charge Calculation
We may think from the above sketch that we have found our perfect Lewis Structure but there is one step left.
We need to calculate the formal charge to check whether all the constituent atoms are in their least possible formal charge values.
To do this, we need to use the below formula:
Formal Charge= Valence Electrons- Lone pair electrons- 0.5* Bonded Electrons
For each oxygen atom, Formal Charge= 6- 6- 0.5*2 = -1
For the sulfur atom, Formal Charge= 6-0-0.5*8=+2
We need to minimize the value of formal charge values. So, a single bond is not enough. We need to create double bonds.
If we consider double bonds in two of the sulfur oxygen combinations, we get the below structure.
Now, if we check the formal charges, we will find out that the formal charge for sulfur is zero, that of the doubly bonded oxygen atoms is zero, and that of the singly bonded oxygen atoms is -1.
So, we got our perfect lewis structure here!
Let us move on to our next topic: Molecular Geometry.
SO42 Molecular Geometry
Once we have deduced the best possible Lewis Structure diagram for our given molecule, we need to delve deeper and find out how our molecule can look in a plane!
Molecular geometry gives us the 3-D representation with a piece of detailed knowledge about how the atoms are bonded and at what angles.
To find out the molecular shape of SO42-, we need to surf the VSEPR theory, short for Valence Shell Electron Pair Repulsion Theory.
Through the VSEPR model, we minimize the repulsion between negatively charged electron clouds surrounding constituent atomic nuclei.
Let us consider the formula AXN:
Here, A stands for central atom, here sulfur.
X stands for the number of bonded atoms to sulfur, here 4. (four oxygen atoms are surrounding the central S), N stands for the bonding and non-bonding pairs of electrons.
Here, if we consider the A and X, we get the resultant formula to be AX4.
So, according to the chart, we can see that SO42- has a tetrahedral structure. The bond angles are almost approximately 109.50 degrees.
Here’s an accurate molecular shape sketch in three dimensions for sulfate ion.
Hybridization is an essential concept of chemical bonding, something that will be handy anytime anywhere when we need to talk about a molecule or learn about its properties.
Hybridization is the theory of atomic orbitals of similar energy levels that fuse and combine to form hybridized orbitals. We find different hybridization in molecules like sp, sp2, sp3, and so on depending on the orbital overlapping.
In the case of sulfate ions, we need to find out the hybridization to understand the overlap of orbitals.
We can find this out by a very simple formula:
Here, H stands for the type of hybridization
V stands for the number of valence electrons concerning the central atom
M stands for monovalent atoms
A and C stands for anionic and cationic charges present inside a molecule.
For sulfate ion, V=6, M=0, A=2, C=0
Therefore H value here is:
H= 0.5(6+0+2-0) = 4
This stands for sp3 hybridization.
Electronic configuration for Sulphur is:
S= [Ne] 3s23p4
If we broaden this we get:
S= [Ne] 3s2 3px2 3py1 3pz1 3d0
If we separate then we get,
S=[Ne] 3s1 3px1 3pz1 3py1 3dxy1 3dyz1
Here, the s and the p orbitals combine and fuse to form the sp3 hybridization while the d orbitals remain unhybridized.
Polarity is the idea that deals with dipole moments and differences in electronegativities( at least 0.5)inside a molecule or ion.
This means that if a compound contains atoms having different electronegativity values i.e asymmetrical electronic distribution, it usually means that it is polar. A polar molecule has partial positive and negative charges inside (δ+ and δ-).
We measure polarity via a term called a dipole moment.
The polarity of Sulfate ion
Do you know that resonance exists in the case of SO42- ion?
For sulfate, we have six resonance structures as we can see in the diagram.
We have already found the perfect Lewis Structure and checked that the molecular shape is tetrahedral.
In SO42-, there are no poles present since the structure is symmetrical.
But this does not signify that there is no ultimate charge since we know that this is an ion having a double negative charge.
Hence, this ion tends to react with other polar compounds despite being non-polar itself. This owes to the fact that the charged molecule has interaction with the partial charge present in any polar compound, for example, H2O( water).
Sulfate ion found in salts naturally and industrially prepared is an important chemical component that we need to learn. We have and will come across a lot of compounds in the future that will bear sulfate ions. So it is necessary to have some knowledge about it to comprehend the possible reactions and physical and chemical properties of the respective compounds. Chemical bonding helps us have a solid and smooth idea about the nitty-gritty of atomic components.
In this article, we have covered Lewis Structure, Molecular Geometry, Hybridization type, and nature of Polarity of SO42- in an extensive format. This will make your learning of sulfate ion all the way easier!