CH3CH2NH2 (ethylamine) has two carbon atoms, seven hydrogen atoms, and one nitrogen atom. In the lewis structure of CH3CH2NH2, there is a single bond between the two carbon atoms. The left carbon atom is attached with three hydrogen atoms, and the right carbon atom is attached with one nitrogen atom. And both (right carbon and nitrogen) are attached with two hydrogen atoms. And on the nitrogen atom, there is one lone pair.
Here’s how you can draw the CH3CH2NH2 lewis structure step by step.
Step #1: draw sketch
Step #2: mark lone pairs
Step #3: mark charges (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 CH3CH2NH2 has two carbon atoms, seven hydrogen atoms, and one nitrogen atom, so…
Valence electrons of two carbon atoms = 4 × 2 = 8
Valence electrons of seven hydrogen atoms = 1 × 7 = 7
Valence electrons of one nitrogen atom = 5 × 1 = 5
And the total valence electrons = 8 + 7 + 5 = 20
- Second, find the total electron pairs
We have a total of 20 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 = 20 ÷ 2 = 10
- 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.
Here, there are two carbon atoms, so we can assume any one as the central atom.
Let’s assume that the central atom is right carbon.
Therefore, place carbons 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 10 electron pairs. And nine bonds are already marked. So we have to only mark the remaining one electron pair as a lone pair 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 is one lone pair, and for carbon, there is zero lone pair because all 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 each carbon atom, formal charge = 4 – 0 – ½ (8) = 0
For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
For nitrogen atom, formal charge = 5 – 2 – ½ (6) = 0
Here, the atoms do not have charges, so no need to mark the charges.
And in the above structure, you can see that the central atom (right carbon) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the stable lewis structure of CH3CH2NH2.
Next: NF2– Lewis Structure