Approaches to teaching the content 

Assessment of what students already know is an important component of making teaching decisions. The key is to have students make connections among the various interrelated concepts in bonding. Students have limited knowledge from GCSE with few connections and even fewer cross-connections. If there are gaps in students’ understanding or if they are missing conceptual links, learning new material is going to be difficult. In fact students do not arrive in the classroom with a clean slate to which knowledge is added. 

The scientific educational literature is full of research that has been done about the difficulty students have in understanding chemical bonding. Many of these misconceptions are robust and remain even after teaching the topic. Common difficulties are: why bonding occurs, confusing ionic bonding with covalent bonding – more in the next section. 

Have you ever wondered if we teach the topic chemical bonding in the correct order? Chemical bonds are still taught as pure ionic and covalent; as well, the role of electronegativity in bonding is often not made clear in ionic bonding. Researchers believe that there are four limitations in the teaching approach. 

• Bonding concepts are arranged on the basis of bond strength – students struggle with the concept of bond strength. 
• Teaching order is by tradition ionic, covalent, polar covalent, hydrogen bonds and London forces. 
• Electronegativity is introduced when polar bonds are introduced. 
• The teaching order is not in line with the bond strength. 

The major problems associated with this order of teaching are that students learn that all types of bonding are independent of each other and that there is no association between them. Researchers have proposed the covalent, polar covalent and ionic bonding sequence for effective teaching. That way you are comparing the product aspect of bonding rather than the process aspect of bonding. 

Teachers working with pre-16 students tend to over-rely on the ‘octet rule’ as an infallible tool for students to use in determining formulae and bonding. This so-called rule contributes to the students’ problems with bonding. This rule has limited application in bonding, and therefore should not be used in teaching chemical bonding, because the octet rule only works successfully for carbon, nitrogen, oxygen and aluminium. 

A range of different terms is used to describe bonds, especially intermolecular bonds. These include ‘van der Waals’, ‘London forces’, ‘intermolecular forces’, ‘attractive forces’ and ‘attractions’. Such language over-complicates the picture. Terms such as ‘induced dipole-dipole bonds’ or ‘permanent dipole – permanent dipole bonds’ are much more descriptive. We need to be consistent in using our bonding terminology. 

Teachers should be aware that their own knowledge of content can cause issues with how information is presented. They should take care not to oversimplify the content. 

Common misconceptions or difficulties students may have 

• Students confuse electron transfer (the process) and electrostatic attraction (the outcome). The latter is ionic bonding.
• Often there is a belief that mobile electrons cause conduction, even in ionic compounds. In ionic compounds, it is the free ions that carry electrical charge. 
• Confusion over electrical conductance – the key idea is that ionic compounds will conduct when molten or in solution because then the ions are mobile. 
• Mistakenly thinking that ions formed by the loss of electrons have a negative charge – whereas it is of course positive as the electron has a negative charge. 
• Why do Group 13 and 15 elements rarely form ionic compounds and Group 14 elements never form ionic compounds? 
• Students often think that boiling simple covalent molecules involves breaking the covalent bonds. Covalent bonds are intramolecular whereas boiling breaks intermolecular forces. 
• They also think that all molecules obey the octet rule – they will meet examples where the octet rule is not adhered to here. 
• Students mistakenly think that any molecule that contains polar bonds must itself be polar – the polarities can cancel out, as in symmetrical molecules. 
• Students become confused between intermolecular forces and covalent bonds – covalent bonds are intramolecular. 
• Students often confuse the conduction of electricity by metals and graphite (electrons) with that of ionic compounds (ions). 
• They see the formulae of ionic compounds written as ‘KCl’ or ‘CaCl₂’. There is no distinction between these formulae and ‘NH₃’ or ‘H₂O’, which are covalent. 
• There are only two types of bonds – covalent and ionic. The vast majority of compounds fall between these two extremes. 
• Covalent bonds are weaker than ionic bonds. 
• Students find it difficult to describe how London forces are formed. 

Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course 

The understanding of bonding is linked in with earlier topics in the syllabus, such as Formulae and equations and Oxidation numbers. It is important to highlight that bonding plays a very important role in Chemistry and will come back in the following topics: Alkanes, Alkenes, Bond enthalpies, Halogenoalkanes, Transition elements, Alcohols, Amines, Amino acids, and Carboxylic acids.