Lewis structure of sulfate ion is drawn in this tutorial step by step. Total valence electrons concept is used to draw the lewis structure of SO42-. In lewis structure of sulfate ion, there should be charges on several atoms due to -2 charge.
Sulfate ion is one of the oxyanion of sulfur. Sulfur is at +6 oxidation state in SO42-. Also, sulfate ion has a -2 charge.
There are two S=O bonds and two S-O bonds in sulfate ion lewis structure. Sulfur atom is the center atom and four oxygen atoms are located around sulfur atom. There are no lone pairs in the last shell of sulfur atom.
Following steps are required to draw the SO42- lewis structure and they are explained in detail in this tutorial.
Drawing correct lewis structure is important to draw resonance structures correctly
There are four oxygen atoms in SO42- ion, Therefore
There are -2 charge on SO42- ion. Therefore there are two more electrons which comes from outside to contribute to the total valence electrons.
Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells
Total electron pairs are determined by dividing the number total valence electrons by two. For, SO42- ion, Total pairs of electrons are 16.
To be the center atom, ability of having greater valance is important. Therefore sulfur has the more chance to be the center atom (See the figure) because sulfur can show valance of 6. Maximum valnce of oxygen is two. So, now we can build a sketch of SO42- ion.
After, marking electron pairs on atoms, we should mark charges of each atom. Each oxygen atom will get a -1 charge and sulfur atom get a +2 charge. The overall charge of ion is ( -1*4 + (+2) ) = -2.
When charges exist everywhere (on atoms) in the ion or molecule, that structure is not stable. We should try to reduce charges on atoms as much as possible. Now, we are going to learn how these facts will affect on sulfate ion.
You see charges of atoms are reduced. Now, there is no charge in one oxygen atom and charge of sulfur atom is reduced from +2 to +1. So we have an stable ion than out previous one.
You should know, sulfur can keep more than eight electrons in its last shell. Therefore we can convert one more lone pair of another oxygen atom to a bond.
In new structure, charges of atoms are reduced than previous structure. Now there are no any charge on sulfur atom and two oxygen atom. Also, only two oxygen atoms have -1 negative charges. Now you understand this structure of SO42- is more stable than previous structures. So, this structure has more chance to be the lewis structure of SO42- ion.
There are 32 electrons in valence shells of all atoms in the ion SO42- ion.
Yes. Compare both lewis structures. Otherwise, we can think an oxygen atom of sulfate ion is replaced by a sulfur atom. Because both sulfur and oxygen belongs to group 6, their valence electrons in last shell is similar.