Q. \( \mathrm{NH_4^+} \) Lewis dot structure.

Goal: Draw the Lewis dot structure for the ammonium ion, \(\mathrm{NH_4^+}\), and explain how to determine the bonding and electron placement step by step.

Step 1: Determine the total valence electrons

Lewis structures use only the valence electrons.

• Nitrogen (N) is in Group 15, so it has \(5\) valence electrons.

• Each hydrogen (H) is in Group 1, so each has \(1\) valence electron. There are \(4\) hydrogens, so \(4 \times 1 = 4\) valence electrons.

• The ion has a charge of \(+1\). A \(+1\) charge means we have lost one electron compared to the neutral atom count.

Total valence electrons:

\[
5 + 4 – 1 = 8
\]

So, \(\mathrm{NH_4^+}\) has \(\mathbf{8}\) valence electrons to place in the Lewis structure.

Step 2: Decide the central atom

In most \(\mathrm{N}\)-\(\mathrm{H}\) compounds, the least electronegative non-hydrogen atom is the central atom.

Here the central atom is \(\mathrm{N}\), and the four \(\mathrm{H}\) atoms surround it.

Step 3: Place bonds first

Ammonium, \(\mathrm{NH_4^+}\), forms four single bonds between nitrogen and hydrogen.

The four \(\mathrm{N-H}\) single bonds are each made of \(2\) electrons (one pair per bond).

Electrons used in bonds:

\[
4 \times 2 = 8
\]

This uses all \(8\) valence electrons.

Step 4: Check for lone pairs on nitrogen

Since all valence electrons have been used to form four bonds, there are no remaining electrons to form lone pairs.

Therefore, \(\mathrm{N}\) has \(\mathbf{0}\) lone pairs.

Step 5: Write the Lewis dot structure

The Lewis dot structure is nitrogen in the center with four single bonds to four hydrogens.

Structure:

\(\mathrm{NH_4^+}\) with four \(\mathrm{N-H}\) single bonds and no lone pairs on nitrogen is:

             H
             |
      H  --  N  --  H
             |
             H

In Lewis notation (equivalently), you can think of it as:

• Each \(\mathrm{N-H}\) bond is a pair of electrons (a single bond).

• No lone pair dots on nitrogen.

Final Answer (Lewis dot structure of \(\mathrm{NH_4^+}\))

\(\mathrm{NH_4^+}\): nitrogen is bonded to four hydrogens by four single bonds, and nitrogen has no lone pairs.