NH4+ (ammonium) has one nitrogen atom and four hydrogen atoms. In the lewis structure of NH4+, there are four single bonds around the nitrogen atom, with four hydrogen atoms attached to it, and none of the atoms has a lone pair.
Also, there is a positive (+1) charge on the nitrogen atom.
Here’s how you can draw the NH4+ 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, nitrogen has five valence electrons and hydrogen has one valence electron.
Since NH4+ has one nitrogen atom and four hydrogen atoms, so…
Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of four hydrogen atoms = 1 × 4 = 4
Now the NH4+ has a positive (+1) charge, so we have to subtract one electron.
So the total valence electrons = 5 + 4 – 1 = 8
- Second, find the total electron pairs
We have a total of 8 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 = 8 ÷ 2 = 4
- 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.
Hence, here we have to assume that the central atom is nitrogen.
Therefore, place nitrogen in the center and hydrogens on either side.
- And finally, draw the rough sketch
#2 Mark Lone Pairs
Here, we have a total of 4 electron pairs. And four N — H bonds are already marked. So we do not have to mark any electron pair as a lone pair on the sketch.
#3 Mark Charges
Use the following formula to calculate the formal charges on atoms:
Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons
For nitrogen atom, formal charge = 5 – 0 – ½ (8) = +1
For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0
Here, the nitrogen atom has a charge, so mark it on the sketch as follows:
In the above structure, you can see that the central atom (nitrogen) forms an octet. Hence, the octet rule is satisfied.
Therefore, this structure is the most stable lewis structure of NH4+.
And since the NH4+ has a positive (+1) charge, mention that charge on the lewis structure by drawing brackets as follows:
Next: NH2– Lewis Structure