Conceptions of chemical bonding

Alternative conceptions of bonding

A topic in science concepts and learners' conceptions and thinking

Science teaching involves teaching scientific concepts, yet these may be difficult to completely characterise, and may prove difficult for many learners to master (a very brief introduction to why this might be can be found at the foot of this page).

This page introduces some issues related to chemical bonding, with links to examples discussed in more detail elsewhere on the site.

Chemical bonding

Chemical bonding is considered one of the core concepts or fundamental ideas in chemistry. It is a topic where there are many common misconceptions and learning difficulties. It is an abstract topic as bonding involves the interactions occurring at submicrosopic (nanoscopic) scales, and it is well know that relating the macroscopic (bench scale) and submicroscopic (molecular) levels of chemistry is challenging for many learners (e.g., Taber, 2013).

Chemical bonding is seen as a process, but younger learners often think of bonds as 'things', and indeed may confuse the links used in physical models of chemical structures as bonds.

Physical models need to use material links to represent bonding (Image by Nobu Hirowumi from Pixabay )
The cause or driving force for bonding

It is very common for learners to think that reactions occur and chemical bonding forms so that atoms can achieve octets of electrons or full outer shells – and they often describe this in anthropomorphic terms (what atoms want, need, try to obtain…) – even though nearly all the reactions they meet in introductory chemistry have reagents where the atoms already have octets/full outer shells (Taber, 1998).

Read about the octet framework

Types of bonding

Students may get confused about the different types of chemical bonding they meet. Amy was not sure how 'ionic bonding' related to 'chemical bonding' (if it did), or how a double bond related to a covalent bond.

Students may interpret texts and introductory teaching to suggest there are only two types of bonding. There are (in this way of thinking) ionic and covalent bonds; and so any chemical bond is one or the other, and therefore if it is not ionic or covalent it is not really bonding! This bonding dichotomy fits well with the octet alternative conceptual framework.

Read about the bonding dichotomy conception and why learners may get 'stuck' on i

Read about a classroom resource to diagnose students' conceptions of what counts as a bond

Ionic bonding

There is a common alternative conceptual framework for thinking about ionic bonding that sees bonds as only existing between ions that have been formed by electron transfer between them (Taber, 1994; 1997). Sometimes students think ionic bonding is electron transfer. This usually leads to students imaging ionic structures as made up of molecules, or molecule-like groups of ions.

Students will often suggest that the lattice structure of NaCl (despite its strong symmetry) includes two types of interactions between neighboring counter ions (Na – Cl): ionic bonds (with one neighbouring ion) and 'just forces' (with the other five neighbours)

Read about the molecular framework for ionic bonding

Read about a classroom resource to diagnose ionic bond misconceptions

Covalent bonding

Chemists often describe covalent bonding as a 'sharing' of a pair of electrons. Although this is a metaphorical term, students may assume the term is mean quite literally. Even when learners have acquired more sophisticated understanding of the nature of covalent bonding, they may consider that 'sharing' is a sufficient explanation of the bond.

Unfortunately, the sharing metaphor is commonly used as if it is a scientific account of the bonding. For example,

"When two particles combine to make a molecule, they usually do so in one of two ways: by electrostatic attraction between two oppositely charged ions (ionic bond [sic-so not forming a molecule!]) or by sharing electrons between two neutral atoms (covalent bond).

Article in the Institute of Physics magazine, Physics World

This seems to suggest that covalent bonding is not due to an electrostatic interaction, but 'sharing'.

Metallic bonding

Traditionally metallic bonding is met after learning about covalent and ionic bonding (there is a good argument for teaching metallic bond earlier – before ionic bonding at least). The students commonly make sense of the structure of metals in terms of their existing knowledge of ionic and covalent bonding (Taber, 2003).

Learners may see metallic bonding as not really chemical bonding because it is not ionic nor covalent – or even because no bonding is needed between atoms of the same type!

Alternatively learners may see metallic bonding as covalent or ionic bonding, or as a variation of ionic or covalent bonding, or as some combination of ionic and covalent bonding.

Or, learners may think that metallic bonding is sufficiently explained as a sea of electrons. Whilst the 'sea of electrons' metaphor/image has educational value some students may see this as a sufficient account of the bonding. If asked to draw this model students often draw a vast excess of electrons (suggesting the 'sea' metaphor is more influential then considering electrical neutrality).

Read about a classroom resource to diagnose metallic bond misconceptions

Hydrogen bonding

Learners sometimes assume that hydrogen bonding is a label given to a covalent bond to a hydrogen atom. (This may be more likely if students have met hydrogen bonding in contexts in biology classes before they have been formally introduced to hydrogen bonding in chemistry lessons).

Other bonding interactions

Interactions which are not ionic, covalent or metallic – such as van der Waals interactions – are sometimes dismissed by learners as not bonding but just forces (bonds understood as sharing or transferring electrons may be seen as quite different form force-based interactions). This can be so even when the interactions are quite significant (such as in solvation).

Bond energy

Bond formation (which can be understood as the outcome of a system of charges/particles being reconfigured to a more stable/lower energy state) is always an exothermic process; and bond formation (which can be understood as reconfiguring a system of charges/particles to a higher energy state) is always an endothermic process. That is, bond breaking always requires an input of energy. It is common for students to associate bond breaking with the release of energy.

A particular case involves the reaction of ATP (adenosine triphosphate) in metabolism, when students may focus on the breaking of the bond in the ATP molecular rather than the overall changes across reactants to products. This is not helped by how the ATP bond that breaks in this process has sometimes misleading been labelled as an 'energy rich phosphate bond'.

Works cited:

Why is teaching and learning of science concepts so difficult: a brief overview

There are many possible ways of conceptualising natural phenomena and science topics. Arguably, we each have somewhat unique and idiosyncratic takes on scientific concepts, so there are always alternative conceptions which overlap and match to varying degrees.

Students often have intuitive ideas about the natural world, or have come across 'folk ideas', which are not consistent with scientific concepts. Some science teaching is regularly misunderstood so misconceptions circulate among students (and may even be found represented in text books).

Scientific theories may be sophisticated and nuanced, and so neither suitable for teaching novice learners nor (even with more advanced learners) for introducing in one step. Science curricula often have simplified and approximate representations of current scientific ideas ('curricula models') set out as target knowledge – so accounts at different levels are not entirely consistent.

Scientific ideas have developed over time, and have become more sophisticated and finely detailed. Many ideas once found useful in science have fallen into disuse either because it is now thought they were actually wrong, or they are no longer seen as helpful ways of thinking about a topic. Many of these ideas that are less developed, out of date, or now discredited, remain as 'conceptual fossils' that can be found in some science texts or more general literature and discourse.

Scientists develop models as thinking tools, often knowing the models are flawed: perhaps only giving approximate outcomes, or only being applicable in limited ranges of situations or they may be purely hypothetical (to be used to think through what would happen if…) without any expectation they reflect nature. Sometimes such models may appear in books to be of similar status to well founded principles laws and theories. Theories themselves vary in the extent to which they are considered to be likely correct, or just a provisional thinking tool.

Scientists, science communicators and journalists, and science teachers, use various techniques to help get a cross novel or abstract ideas: these can include analogies, similes, metaphors, narratives, and so forth. Sometimes these ideas get repeated and used so often they may seem to be part of the scientific idea, rather than just a linguistic tool. Indeed, sometimes terms originally used metaphorically become so widely adopted that they take on a new scientific meaning somewhat different form the original meaning.

Given all of that, it is not surprising that learning and teaching science can be quite challenging!

ChemTeach – is a discussion list for sharing information and expertise among those involved in teaching chemistry. Click here to learn more about, or find out how to join, the group

facebookShare on Facebook
TwitterTweet