Modelling Chemical Bonds

Overview

Students build on their understanding that covalent bonds involve sharing electrons between non-metals. They will use ball-and-stick models and diagrams to represent molecules, explain how shared electrons form bonds, and begin comparing covalent bonding with metallic bonding.

Learning intentions

Students will:

• represent simple covalent molecules using ball-and-stick models and electron diagrams
• explain how shared pairs of electrons hold non-metal atoms together
• distinguish between single and multiple covalent bonds
• describe the basic model of metallic bonding as positive ions in a lattice surrounded by delocalised electrons
• develop a testable question about how bonding relates to material properties

Success criteria

• I can construct and draw accurate models of simple covalent molecules.
• I can identify shared electrons and explain their role in a covalent bond.
• I can distinguish a single, double and triple covalent bond.
• I can describe one difference between covalent and metallic bonding and link it to a material property.

Curriculum links

• Materials — assessing materials using physical and chemical properties.
• Reactions — describing chemical structures and bonding in context.
• Working scientifically — developing questions and hypotheses for scientific investigation.
• Working scientifically — selecting and using scientific tools for accurate observations and representations.

Lesson structure (60 minutes)

1. 0–5 min · Hook and retrieval. Open with the opening question and bonding image and display the question: “Why can copper be bent into wire while carbon dioxide is a gas?” Students individually recall what they know about metals, non-metals, electrons and covalent bonding, then share one idea with a partner.

2. 5–15 min · Explicit teaching: covalent bonding. Use the covalent bonding explanation to review that non-metal atoms share electrons to gain a more stable outer shell. Model hydrogen, chlorine, water and carbon dioxide, showing that a line between atoms represents one shared pair of electrons. Emphasise that the atoms remain joined because the shared electrons are attracted to both nuclei. Students annotate the corresponding examples on the bonding model worksheet.

3. 15–32 min · Ball-and-stick modelling. In pairs, students use molecular model balls and connectors to construct hydrogen, chlorine, water, carbon dioxide and methane. Refer to the model-building instructions and molecule prompts. Students record each molecule’s atoms, number of bonds and whether it contains single or multiple bonds on the bonding model worksheet. Circulate and check that students do not confuse the number of connectors with the number of atoms.

4. 32–40 min · From models to diagrams. Demonstrate how to convert a three-dimensional model into a two-dimensional structural diagram and a simple electron-dot representation. Students draw two assigned molecules, label each atom and circle every shared electron pair. Pause for a check: “How many shared pairs are around the central atom in carbon dioxide?” Students use mini whiteboards or the worksheet to show their response.

5. 40–50 min · Introducing metallic bonding. Use the metallic bonding comparison diagrams to introduce the model of a regular lattice of positive metal ions surrounded by delocalised electrons. Explain that the electrons are not shared between particular pairs of atoms, unlike in covalent molecules. Students complete a comparison table on the bonding model worksheet, including particle arrangement, electron behaviour and one expected property. Avoid presenting this as a complete explanation of all metal properties; describe it as a useful model.

6. 50–56 min · Question and hypothesis challenge. Students develop a question such as, “How might the type of bonding affect whether a substance conducts electricity?” They write a prediction using the frame: “If a substance has ______ bonding, then it may ______ because ______.” Invite two or three students to share. Use the investigation question prompts to support students in making questions measurable and scientifically relevant.

7. 56–60 min · Plenary and exit check. Display the final retrieval questions. Students answer: “What is a covalent bond?”, “What does one line represent in a structural diagram?” and “What is one difference between covalent and metallic bonding?” Collect the bonding model worksheet or photograph responses for formative assessment.

Resources

• the covalent and metallic bonding slide deck
• the bonding model worksheet
• Molecular model balls and connectors, ideally including different colours for different elements
• Mini whiteboards and markers
• Student exercise books and coloured pencils
• Periodic table reference sheets
• Safety glasses if model components are shared laboratory equipment
• Board or display panel for teacher modelling

Assessment

• Check students’ retrieval responses and questioning during the opening review.
• During modelling, assess whether students correctly represent atom types, shared pairs and single or multiple bonds.
• Use the comparison table and final responses to identify misconceptions, particularly the belief that covalent bonds transfer electrons or that metallic bonding involves fixed shared pairs.

Differentiation

• Provide a molecule bank showing the formula, atom colours and completed example for students requiring support. Offer sentence starters for explanations and hypotheses.
• Pair students strategically and assign roles such as builder, diagram drawer and accuracy checker; allow students to explain orally before writing.
• For EAL/D learners, use labelled visuals for atom, nucleus, outer-shell electron, shared pair, lattice and delocalised electron. Explicitly teach that “delocalised” means not attached to one particular atom.
• Extend confident students by asking them to model nitrogen or oxygen, explain why multiple bonds are represented differently, and propose a fair investigation comparing electrical conductivity of materials.