NH2- Lewis Structure

NH2- Lewis Structure

NH2 (azanide) has one nitrogen atom and two hydrogen atoms. In the lewis structure of NH2, there are two single bonds around the nitrogen atom, with two hydrogen atoms attached to it, and on the nitrogen atom, there are two lone pairs.

Also, there is a negative (-1) charge on the nitrogen atom.

Steps

Here’s how you can draw the NH2 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

In the periodic table, nitrogen lies in group 15, and hydrogen lies in group 1.

Hence, nitrogen has five valence electrons and hydrogen has one valence electron.

Since NH2 has one nitrogen atom and two hydrogen atoms, so…

Valence electrons of one nitrogen atom = 5 × 1 = 5
Valence electrons of two hydrogen atoms = 1 × 2 = 2

Now the NH2 has a negative (-1) charge, so we have to add one more electron.

So the total valence electrons = 5 + 2 + 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
NH2- Lewis Structure (Step 1)

#2 Mark Lone Pairs

Here, we have a total of 4 electron pairs. And two N — H bonds are already marked. So we have to only mark the remaining two electron pairs as lone pairs on the sketch.

Also remember that nitrogen is a period 2 element, so it can not keep more than 8 electrons in its 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. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for nitrogen, there are two lone pairs.

Mark the lone pair on the sketch as follows:

NH2- Lewis Structure (Step 2)

#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 – 4 – ½ (4) = -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:

NH2- Lewis Structure (Step 3)

In the above structure, you can see that the central atom (nitrogen) forms an octet. Hence, the octet rule is satisfied.

Now there is still a negative (-1) charge on the nitrogen atom.

This is okay, because the structure with a negative charge on the most electronegative atom is the best lewis structure. And in this case, the most electronegative element is nitrogen.

Therefore, this structure is the most stable lewis structure of NH2.

And since the NH2 has a negative (-1) charge, mention that charge on the lewis structure by drawing brackets as follows:

NH2- Lewis Structure (Final)

Next: AlCl3 Lewis Structure

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