Lewis structure of NO3- ion is drawn step by step in this tutorial. Total valence electrons of nitrogen and oxygen atoms and negative charge are considered to draw the NO3- lewis structure. You will every fact of drawing lewis structures from this tutorial which will help you to draw more lewis structures in the future.
Now, we are going to learn, how to draw this lewis structure of NO3- ion.
Following steps are required to draw NO3- lewis structure and they are explained in detail in this tutorial.
There are one nitrogen atom and three oxygen atoms in the nitrate ion. Also there is a -1 charge on the nitrate ion.
Nitrogen and oxygen are located at VA and VIA groups respectively in the periodic table. So nitrogen has five electrons in its valence shell. In oxygen atom, there are six electrons in its valence shell.
There are three oxygen atoms in NO3-, Therefore
Due to -1 charge, another electrons is added
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, NO2-, there are 24 valence electrons, so total pairs of electrons are 12.
To be the center atom, ability of having greater valance is important. Nitrogen can show valence,5. But, oxygen's maximum valence is 2. Therefore nitrogen has the more chance to be the center atom (See the figure). So, now we can build a sketch of NO3- ion.
There are already three N-O bonds in the sketch. Therefore only nine valence electrons pairs are remaining to draw the rest of ion.
Start to mark those nine valence electrons pairs on outside atoms (oxygen atoms) as lone pairs. One oxygen atom will take three lone pairs following the octal rule (oxygen and nitrogen atoms cannot keep more than eight electrons in their valence shells). All nine valence electrons pairs (9) are spent when lone pairs are marked on oxygen atoms.
Therefore, there is no ine valence electrons pairs to mark on nitrogen atom.
Check charges on atoms and mark them as below. Charges are important to decide the lewis structure of the ion.
The drawn structure for NO3- is not a stable structure because oxygen atoms and nitrogen atoms have charges. When a molecule or ion has so many charges on atoms, that structure is not stable.
Now, we should try to minimize charges by converting lone pair or pairs which exist on oxygen atoms to bonds. So we convert one lone pair of one oxygen atom as a N-O bond.
Now there is a double bond between nitrogen and one oxygen atom. There are also two single bonds (N-O) with nitrogen atom and other oxygen atoms.
In new structure, charges of atoms are reduced. Now there is no any charge on one oxygen atom. Also, charge of nitrogen atom is reduced from +2 to +1. Now you understand this structure of NO3- is more stable than previous structure due to less charges on atoms.
But, We cannot convert more lone pairs of other oxygen atom to make a bond with nitrogen atom because nitrogen cannot keep more than eight electrons in its last valence shell.
No electrons pairs exist on nitrogen atom. But, on nitrogen atom, there is a +1 charge. Around the nitrogen atom, there are two single bonds and double bond.