How to draw dot and cross diagrams

1 Comment

Spur your students on with this step-by-step approach to covalent bonding

Cartoon molecule models and electron shell diagrams

Source: © Dan Bright

Once they have mastered electron configuration diagrams, show your learners how they can adapt them to show structure and bonding in covalent and ionic compounds. These structural diagrams depict only the outer, or valence, shell electrons and are known as dot and cross diagrams. Electrons from different atoms use alternating symbols, usually a dot and a cross, to show which atom the electrons have come from.

Let’s take a closer look at some compounds containing nitrogen. Remember that nitrogen has five electrons in its outer shell.

How to draw a dot and cross diagram for ammonia

In NH₃, commonly known as ammonia, nitrogen forms three single covalent bonds with three hydrogen atoms.

Source: © Dan Bright

Source: © Dan Bright

Source: © Dan Bright

Source: © Dan Bright

While you are learning how to draw dot and cross diagrams it’s useful to start with something you are already familiar with: electron configuration diagrams. Sketch out the electron configuration diagrams for each of the atoms.

Draw the outer shell of each atom. It’s a good idea to draw the electrons in pairs but remember to use a pencil as you may have to move the electrons around to fit the structure. You don't need to put a circle around the symbol for the nucleus.

Arrange the atoms so that the valence electrons will complete the outer shells of all the atoms in a simple covalent molecule. While you are learning, draw each atom on a small piece of paper so you can easily rearrange them.

Draw the completed dot and cross diagram. Here we have changed the electrons on the hydrogen atoms to be dots. You can alternate the dots and crosses in simple diagrams or use other colours or symbols for larger diagrams. This dot and cross diagram shows the outer shells touching.

This method is easiest for single covalent bonds as there is not much room where the atoms’ shells touch for drawing lots of electron pairs.

Download this

Infographic poster, fact sheet, worksheet and teacher notes. Display the poster in your classroom or on a projector. Alternatively, print it and use it as a handout.

Use the accompanying fact sheet and worksheet to get your students practising dot and cross diagrams. Go to the accompanying resource for further information about how to use the Covalent bonding tiles.

Poster as pdf
Fact sheet as MS Word or pdf
Covalent bonding tiles student worksheet as MS Word or pdf
Covalent bonding tiles teacher notes and answers as MS Word or pdf

DOWNLOAD ALL

How to draw double and triple bonds

This first method (blue background) is useful for double and triple bonds as it gives more space for drawing electrons. This second method (pink background) is useful for checking that you have drawn the right number of electrons in the outer shell of each atom.

Source: © Dan Bright

Source: © Dan Bright

Source: © Dan Bright

Nitroxyl contains a single covalent bond between hydrogen and nitrogen and a double covalent bond between nitrogen and oxygen.

Draw the dot and cross diagram with the outer shells overlapping. Then draw the shared electrons inside the overlapping section.

Nitrogen gas occurs naturally as a diatomic molecule. The bond between the two nitrogen atoms is a triple bond.

Again, draw the dot and cross diagram with the outer shells overlapping. However, this time draw the electrons on the lines rather than in the space between.

More resources

Spot misconceptions that learners may have when identifying the type of bonding in various chemical compounds with this student worksheet.
Ensure that students have a strong foundation in drawing electron configuration diagrams with this infographic, fact sheet and worksheet.
Use this activity to help learners develop an understanding of covalent bonding in terms of energetic stability rather than full shells.
Inspire students to share their passion for chemistry by becoming a science communicator or teacher.

Want another step-by-step guide to drawing bonds? Check out this article with resources on drawing dot and cross diagrams for ionic bonding.