Question

How to draw Lewis dot structure of ${{\mathrm{SO}}_4}^{2-}$ and ${{\mathrm{NO}}_2}^{-}$?

Answer 1

Steps to draw the lewis structure:

• Lewis dot structures are diagrams that show the bonding between atoms of a molecule, as well as lone pairs of electrons that may exist in the molecule.
• First, we have to find out how many valence electrons are in the molecule.
• Then, draw a skeletal molecule in which the central atom forms a single bond with each of the other atoms. The least electronegative element will make up the center atom.
• Now, fill the octet of the most electronegative element and then the other elements.
• Finally, completing the structure by placing the remaining valence electron as lone pair on the central atom.

Lewis dot structure of ${{\mathrm{SO}}_4}^{2-}$:

• Total valence electrons in ${{\mathrm{SO}}_4}^{2-}$ = Valence electron of Sulfur $+$ Valence electron of oxygen
• Valence electrons $=6+4\times 6+2=32$
• There is a $-2$ charge on Sulfate ion which contributes to valence electrons.
• Sulfur is the central atom and four oxygen atoms are located around the sulfur atom
• Adding electron pair between Sulfur and oxygen to represent a chemical bond.
• Now, completing octet of Oxygen i.e. $8$electrons around each oxygen.
• There are no electrons left from the valence electrons.
• There are two $\mathrm{S}=\mathrm{O}$ bonds and two $\mathrm{S}-\mathrm{O}$ bonds in the Sulfate ion Lewis structure.

Lewis Dot Structure of ${{\mathrm{NO}}_2}^{-}$:

• Total valence electrons= Valence electron of Nitrogen $+$ Valence electron of Oxygen
• Valence electrons= $5+6\times 2+1=18$
• Due to one negative charge, one electron will be added.
• In the Lewis dot structure for Nitrate ion Nitrogen atom is the least electronegative atom and goes at the center of the structure surrounded by two oxygen atoms.
• Placing one electron pair to show the chemical bond between each Nitrogen and Oxygen. Now we are left with $14$ valence electron
• Assigning the electrons such that the octet of nitrogen and oxygen is completed.

Therefore, From the octet rule, we can draw the Lewis dot structures.