||What are 'hydrogen bonds' and where are they found?
These activities introduce hydrogen bonds as intermolecular bonds made between specific permanent dipoles. Students work through a cognitive conflict exercise, a simple experiment and then carry out research on a material containing hydrogen bonds.
Students will understand that hydrogen bonds:
- are intermolecular bonds formed between hydrogen atoms and an atom of nitrogen, oxygen or fluorine in a separate molecule
- are present in a wide range of chemicals
- require more energy to break than other types of intermolecular bond.
Sequence of activities
Give each student a small piece of paper.
Ask them to watch while a beaker of water is boiled in front of them.
When the water is fully boiling, ask them to write on the paper what they think is in the bubbles.
Take in the pieces of paper and write the range of responses on a board.
Indicate that there can only be one correct answer.
Responses are most likely to say ‘hydrogen and oxygen’, ‘carbon dioxide’, ‘oxygen’, ‘hydrogen’. A few will say ‘water vapour’ or ‘steam’ (either is correct).
Divide the class into groups of three or four.
Ask the groups to:
- discuss the responses and decide on the one correct answer, with reasons
- work out explanations for why the remaining answers are incorrect or incomplete.
In a plenary:
- hear each group’s responses
- indicate the correct answer clearly after hearing all groups
- use molecular models of water molecules to show what happens when water boils
- introduce the term hydrogen bond to explain how water molecules bond together
- ask students to write a short explanation about what happens when water boils
- describe the learning objectives.
Explain that other molecules besides water contain hydrogen bonds and that ‘slime’ is a polymer containing hydrogen bonds that can be made easily.
To each student, give a copy of the worksheet
Supervise the practical work as students make slime and investigate its properties.
In a plenary:
- invite students to describe the properties of slime and what uses it may have
- introduce the idea that other materials with hydrogen bonding may be more useful!
Explain the next activity, to research one material that contains hydrogen bonding.
Hand out Finding out more.
Support students as they:
- re-form into groups
- decide which material to investigate (ensure that each group investigates a different material)
- carry out their research
- prepare their presentation
- agree criteria for assessing each other’s presentations.
Clarity of information presented.
Quality of explanations.
Details about the material.
Extent to which the brief was covered.
Arrange for each group to make its presentation.
Support them as they subsequently assess the presentations and give feedback to each other.
Ask the students to write, and hand in, a summary about hydrogen bonding based on the information presented.
Give written feedback to students, indicating the extent to which they have grasped the key ideas, together with advice on how to develop their understanding.
Assessment for learning commentary
The introductory exercise uses cognitive conflict and peer discussion to prompt students to correct misconceptions about state change, and to introduce hydrogen bonds. Sharing the objectives is necessarily delayed until after this.
By its nature, the experiment continues the hydrogen bond theme in a lively way. The research task uses peer assessment to learn and apply knowledge about hydrogen bonds to unknown situations.
Teacher feedback on written summaries can highlight what individuals understand, together with pointers for development.
For each student
||Finding out more
For each student
- Polystyrene cup
- Wooden lolly stick
- Food colouring
- 50 cm3 4% polyvinylalcohol (poly(ethenol)) (Toxic)
- 10 cm3 4% sodium borate solution (Toxic).
For each group
- Access to internet and books for research
- Presentation materials, eg access to IWB, OHP, OHTs and marker pens, paper and pens.
Procedure to make 4% poly(ethenol) solution
- This is best done on a magnetic stirrer with a heating element.
- Boil 100 cm3 water in a 250 cm3 beaker.
- Gradually add 4 g poly(ethenol) while stirring.
- After about 10 minutes a colourless, viscous solution will form.
- Do not allow the solution to boil, otherwise the polymer chains will degrade.
It is the responsibility of the teacher to carry out an appropriate risk assessment.
- The ‘slime’ should not be eaten.
Structure of slime
Making slime questions
- Slime can stretch and snap.
- See diagram.
- Hydrogen bonds and instantaneous dipole ‑ induced dipole bonds.
- Any valid suggestions.
- If slime was not water soluble it could be used in modelling (eg like Fimo).
R. Osborne and P. Freyberg, Learning in science: The implications of
children's science. Portsmouth, New Hampshire, US: Heinemann, 1985.
G. Burton, J. Holman, G. Pilling and D. Waddington, Salters Advanced Chemistry. Oxford: Heinemann, 1994.