Drawing a Lewis structure can be broken down into a general steps which makes it much easier to draw. Before starting, you will notice when drawing a Lewis structure, you want to have 8 valence electrons on each atom because that is what most atoms valance shell holds. Helium and hydrogen are exceptions. If it is a hydrogen atom, there is only two electrons around it because hydrogen’s valence shell only holds 2.
How to Make a Lewis Dot Structure… the Basics
Find the most neutral atom will be the one closest to row 4. So your compound is CH2O then your most neutral atom is Carbon. If your center is SF2 then your most neutral atom is Sulfur and so on. I am going to be using water (H2O) for my example.
Draw your most neutral atom first. Once you have this, evenly space your other atoms around the center one. Then place your electrons around the atoms. Oxygen has 6 electrons and hydrogen has 1.
Now when you have two dots in a row, then you can change that into a line. A line (single bond) represents two shared electrons. A line counts as two valence electrons for both atoms that share that single bond. Dots count as one electron for the atom it is around. So after connecting them, you have 8 around the Oxygen and 2 around each helium, as shown on the right and as talked about above.
This is the Lewis dot structure, but usually they group the dots together on the same side of the atom, which would leave you with what is on the right.
How to Draw More Difficult Lewis Structures
For this explanation, I am going to be using acetone. Acetone’s formula is (CH3)2CO. This may look confusing on where to start, but using the rules I provided above, Carbon is your most neutral atom. This means start with this one. Because you have 3 carbons, start with all 3. Since this has many atoms in the molecule, it may help to draw the valence electrons as we add the atoms.
After placing 3 carbons, you have 6 hydrogen and 1 Oxygen left. Since I have 6 hydrogen, and hydrogen are usually found toward the outside of lewis structures, add them to the outside carbons. Now you are left with just Oxygen. Add this to the middle Carbon because it is the only spot left.
Now that you have all the atoms, where ever there are two dots between atoms, make that into a line.
You are left with what is on the right, everything is has lines except the oxygen has 4 extra valence electrons.
Time to Check
To check if everything is right, make sure all atoms have 8 valence electrons except hydrogen that only has 2. All the helium atoms only have 1 single bond (single line), therefore, they all have 2 valence electrons. They helium atoms are all correct. The right and left carbons both have 4 single bonds, so they all have 8 valence electrons. The middle carbon has 2 single bonds (one line) and 1 double bond (2 lines). This carbon still has 4 “lines,” so it is also correct. The oxygen has 1 double bond, and 4 dots. 1 double bond=2 lines= 4 valence electrons +4 dots (also 4 valence electrons), this is also correct.
This is how to draw Lewis dot structure!
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