CH2NH (methylene imine) has one carbon atom, three hydrogen atoms, and one nitrogen atom. In the lewis structure of CH2NH, there is a double bond between the carbon and nitrogen atom. The carbon atom is attached with two hydrogen atoms, and the nitrogen atom is attached with one hydrogen atom. And on the nitrogen atom, there is one lone pair.
Here’s how you can draw the CH2NH lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges
Step #4: minimize charges
Step #5: minimize charges again (if there are)
Let’s break down each step in detail.
#1 Draw Sketch
- First, determine the total number of valence electrons
Hence, carbon has four valence electrons, hydrogen has one valence electron, and nitrogen has five valence electrons.
Since CH2NH has one carbon atom, three hydrogen atoms, and one nitrogen atom, so…
Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of three hydrogen atoms = 1 × 3 = 3
Valence electrons of one nitrogen atom = 5 × 1 = 5
And the total valence electrons = 4 + 3 + 5 = 12
- Second, find the total electron pairs
We have a total of 12 valence electrons. And when we divide this value by two, we get the value of total electron pairs.
Total electron pairs = total valence electrons ÷ 2
So the total electron pairs = 12 ÷ 2 = 6
- Third, determine the central atom
Here hydrogen can not be the central atom. Because the central atom is bonded with at least two other atoms, and hydrogen has only one electron in its last shell, so it can not make more than one bond.
Now we have to choose the central atom from carbon and nitrogen. Place the least electronegative atom at the center.
Since carbon is less electronegative than nitrogen, assume that the central atom is carbon.
Therefore, place carbon in the center and hydrogen and nitrogen on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 6 electron pairs. And four bonds are already marked. So we have to only mark the remaining two electron pairs as lone pairs on the sketch.
Also remember that both (carbon and nitrogen) are the period 2 elements, so they can not keep more than 8 electrons in their last shell. And hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell.
Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens and nitrogen. But no need to mark on hydrogen, because each hydrogen has already two electrons.
So for nitrogen, there are two lone pairs, and for carbon, there is zero lone pair because all two electron pairs are over.
Mark the lone pairs on the sketch as follows:
#3 Mark Charges
Use the following formula to calculate the formal charges on atoms:
Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons
For carbon atom, formal charge = 4 – 0 – ½ (6) = +1
For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For nitrogen atom, formal charge = 5 – 4 – ½ (4) = -1
Here, both carbon and nitrogen atoms have charges, so mark them on the sketch as follows:
The above structure is not a stable lewis structure because both carbon and nitrogen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.
#4 Minimize Charges
Convert a lone pair of the nitrogen atom to make a new C — N bond with the carbon atom as follows:
In the above structure, you can see that the central atom (carbon) forms an octet. Hence, the octet rule is satisfied.
Also, the above structure is more stable than the previous structures. Therefore, this structure is the stable lewis structure of CH2NH.
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