Question

What are the steps used to draw a Lewis structure?

Answer 1

Here are the steps that I use to draw a Lewis structure.

1. Decide which atom is the central atom in the structure.
2. Draw a skeleton structure in which the other atoms are single-bonded to the central atom.
3. Draw a trial structure by putting electron pairs around every atom until each gets an octet.
4. Count the valence electrons in your trial structure.
5. Now, count the valence electrons you have available.
6. Add or remove electrons in the trial structure to match the available electrons.
7. Assign formal charges to each atom.

EXAMPLE

Draw the Lewis structure of the ammonia, `"NH"_3`

Solution

1. Central atom

`"N"` has to be the central atom, because `"H"` mus be a terminal atom.

2. Skeleton structure

`"H—N—H"`
`color(white)(mml)|`
`color(white)(mm)"H"`

3. Trial structure

`"H—"stackrelcolor(blue)(..)("N")"—H"`
`color(white)(mml)|`
`color(white)(mm)"H"`

4. Valence electrons shown

`"Valence electrons shown" = 8`

5. Electrons available

`"Electrons available" = 5 + 4(1) - 1 = 8`.

∴ The trial structure is the correct structure.

6. Correct structure

Already done.

7. Formal charges

`"N" = 5 - [2 + ½(6)] = "5 - 5" = 0`

`"H" = 1 - ½(2) = 0`

The Lewis structure of `"NH"_3` is

`"H—"stackrelcolor(blue)(..)("N")"—H"`
`color(white)(mml)|`
`color(white)(mm)"H"`