Practical advice for new teachers: 5 ways to improve your students chemical bonding exam answers.

Chemical bonding is a big topic in the Edexcel IGCSE chemistry specification. It covers ionic, covalent, and metallic bonding. Covalent bonding is divided into simple covalent molecules and giant covalent structures. Teaching this topic as a new teacher not only requires excellent subject knowledge, but a thorough understanding of the specification and what examiners are looking for.

There are a lot of keywords in this topic that sound similar and are often mis-used by students costing them marks. For example, when should atoms, molecules or ions be mentioned? What about when to use the words bonds or forces? Students often think of them as the same thing and use them interchangeably.

Questions range from low demand recall to challenging 6-mark questions asking students to compare several structures and their properties. Yes, bonding is a big topic with lots of technical details. It can, at times, be hard to imagine what we are talking about. It’s an abstract topic that lends itself to using moly mod kits to help students visualize the bonds and forces.

If you are new to teaching chemical bonding, here are 5 common misconceptions that show up year on year when teaching this topic. Highlight these issues early on in your lesson plans. Embed lots of retrieval practice to get your students confident in their understanding of chemical bonding and on their way to achieving full marks.

1. Intermolecular vs. Intramolecular

‘Weak intermolecular forces’ is the key term needed to hit marks on the mark scheme when describing covalent molecules. Students often mistake intermolecular forces for the covalent bonds holding the atoms together in the molecule.

To address this misconception, I use the moly mod kits as part of my lessons on covalent molecules. Moly mod kits are like Lego but for chemistry. They are great at allowing students to visualize molecules in 3D.

My go-to activity is to ask every student in the class to build a molecule of carbon dioxide. Everyone is then asked to bring their molecule and lay it on a large piece of sugar paper on a front table. I will then come in and label the intermolecular forces and intramolecular bonds as shown in the picture below. This is a good time to tell the students that it is the intermolecular forces that break upon heating. State that they are weak and break with little energy, this is why covalent molecules have low boiling points and tend to exist as liquids and gases at room temperature.

Students sometimes can’t tell the difference between intermolecular and intramolecular forces. Let’s help them learn the difference between “inter” and “intra.”

2. Confusing Forces with bonds.

Bonds are strong and between atoms or ions. Forces are weak, temporary and exist between molecules. Students use the words interchangeably.

Look at the question below and read the student response. How many marks is it worth and how can we improve it?

The question has been answered with the right ideas but will lose an easy mark as the student has written the word ‘bonds’ between the molecules. As bonds have been mentioned twice, 2 marks have been lost.

Here is a draft of the correct answer with the improved terminology:

Carbon dioxide has a low boiling point because it has weak intermolecular forces between the molecules. These forces do not need much energy to break, so it boils at a low temperature. An easy fix for full marks.

3. Identifying the Structure Type

Students have a lot of trouble identifying whether a question is asking about a covalent, ionic or metallic structure. The topic becomes even more challenging when students are given an unfamiliar structure and must apply their knowledge.

Example: The Edexcel IGCSE Chemistry June 2024 paper used caffeine in its bonding question. Caffeine (C₈H₁₀N₄O₂), is not mentioned in the specification textbook as an example, but students were expected to recognize that it is a simple covalent molecule.

Teacher Tip: Some shortcut rules to help students identify substances

1. Ionic compounds – have a giant structure. Occurs when metal atom transfers its valence electrons to a non-metal atom.
2. Simple covalent molecules – involve non-metal atoms only. Usually identified as group of atoms that exist as lots of separate molecules (e.g. water H2O, CO2)
3. Giant covalent molecules– occurs between non-metal atoms only. Involves a large network of atoms joined by covalent bonds.
4. Metallic structures– involve metal atoms only, represented as rows or positive metal ions surrounded by a sea of delocalized electrons.

Use my worksheet below to support student recall and confidence in using these keywords.

4. Electrostatic attraction, Where is it?

Electrostatic attraction makes an appearance in ionic, covalent and metallic bonding. Students often confuse it with covalent bonds or just try to include in their answers in the hope of gaining some marks.

The key teaching point here is to make sure students understand that electrostatic attraction is a strong force. It happens between oppositely charged particles. So, let’s have a look at each substance and where to mention the existence of electrostatic attraction.

Ionic compounds– electrostatic attraction is between the positive and negative ions in the lattice structure.

Covalent molecules – Molecules consist of a small group of atoms. Electrostatic attraction is between the atom’s positively charged nuclei and negatively charged shared pair of electrons within the covalent bond.

Metallic structures – Electrostatic attraction is between the positively charged metal ions and negatively charged delocalized electrons.

5. Fullerenes are simple covalent molecules?

Fullerenes have the chemical formula (C₆₀), students often see the large number of carbon atoms as a large network and write about fullerenes as giant covalent structures. Clear this misconception early by using moly mod kits to join 60 carbon atoms forming a molecule. If this is done as a class activity, you will end up with several fullerene molecules that can be displayed to help visualize the weak intermolecular forces.

Students will then be able to apply the structure and properties of simple covalent molecules such as water and carbon dioxide with fullerenes to achieve full marks.

Summary:

Highlight keywords when teaching chemical bonding to your IGCSE Chemistry classes. Students need to know the difference between forces bonds, intermolecular and intramolecular. Support students with identifying ionic, covalent and metallic structures.

Chemical bonding is a challenging and abstract topic for students. Utilize moly mod kits in your lesson plans regularly to help visualization. Retrieval practice on a regular basis will help students embed the key terminology in their memory, this is essentially what examiners are looking for when marking.

Starter activities provide a great opportunity for retrieval practice. Some examples of quick-fire recall questions that build confidence in the topic are below. Aim for 5 recall questions at the start of every lesson while teaching this topic to help your students score full marks on chemical bonding.

1. Name an ionic compound
2. Where are weak intermolecular forces
3. Where is the electrostatic attraction in a metallic structure.
4. State what type of structure a fullerene is?
5. Describe a covalent bond.