Writing Lewis Dot Structures

Before you start you should know how to predict valence electrons (or you will feel lost when you attempt to do this). For a quick reminder, click here.

Things you will need:

A periodic table

Pencil & Paper

Here's a link to the online tutorial we did in class:

Lewis Dot Structure Tutorial

If you want to see notes or videos on how to do this continue on below :-)

Single atom Lewis dot structures:

You should have this memorized:

Write the symbol

A) Look up valence electrons

B) Assign electrons in a circular pattern: 1 electron on all sides then begin pairing electrons.

C) Each side represents an orbital that can hold 2 electrons. In these diagrams, you are showing valence orbitals only.

D) Remember that electrons have the same charge so they first seek out separate orbitals.

So Lewis Dot structures such as H, C, Br, & Xe would look like this:

In all actuality most atoms do not exist as monatomic structures. Let's move on to molecules with multiple atoms:

In biology we studied a very important molecule O₂ (molecular oxygen). This substance allows us to do all the things that make us human. Oxygen is an example of a Diatomic molecule (Molecules that contain two atoms, and they are both the same type of element).

Draw the lewis Dot Structure for O₂

Videos on how to draw Lewis Dot Structures Below:

_{Step 1}

_{Start by drawing the lewis dot structure for the individual elements involved. In this example you only need to draw this for Oxygen since there are no other element types. See the picture below for the answer (and some notes about what you are looking at).}

_{Why? This gives you an idea of where an element can hook up (bond) to other atoms.}

Step 2 Count up the valence electrons (used to check yourself later)

To do this, take the number of valence electrons for each type of element in your molecule and multiply it by the total number of atoms.

In this example:

O has 6 valence electrons X 2 oxygen atoms

= 12 electrons to spend in your finished drawing.

Step 3 Arrange the atoms so that half empty orbitals (sides that only have a single electron) are touching. Note that it does not matter how you face them on the page. If you aren't sure how to place an atom see the "HONC" rule on the right side of this page.

The HONC Rule:

Hydrogen makes only 1 bond

Oxygen makes up to 2 bonds

Nitrogen makes up to 3 bonds

Carbon makes up to 4 bonds

Use the atoms that make the most bonds as your centerpieces for your molecules

Step 4 For any left over single electrons (not lone pairs) resolve this by forming double or triple bonds. You cannot have any more than a triple bond.

Polyatomic compounds (compounds with 2+ element types):

Draw the Lewis Dot Structure for methane. Formula: CH₄

To draw a Lewis Dot Structure for a molecule you will need to Create Lewis structures for the basic atoms that make up the molecule first.

Example: Methane CH₄

Write out your basic Lewis Dot structures:

Count up your valence electrons and total them.

1 carbon = 4 valence electron

4 Hydrogen atoms = 4 valence electrons

In the example above we have 8 valence electrons to spend. Use this to check your final drawing (if it exceeds or goes below this number you may want to rework the problem).

The first letter is usually the "center atom" Any place that has only 1 electron can bond with another atom.

Sides that have 2 electrons are called lone pairs. Lone pairs and empty sides DO NOT bond. This can account for bending of certain molecules you will draw later.

Three types of bonds to accomidate your Lewis Dot Structure:

Single bond = 2 shared valence electrons

Double bond = 4 shared valence electrons

Triple bond = 6 shared valence electrons

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