3. Using pair work to support understanding
Careful questioning, providing opportunities for students to discuss their ideas, and open-ended writing, are all techniques that will help you to find out the level of understanding in your class. Another helpful approach is to get your students to make a model or draw a picture to explain a scientific idea or principle.
As your students develop their understanding of chemical compounds, you will be introducing them to chemical formulas. Chemical formulas provide a universal way for chemists to talk to each other, and it is important that your students understand what they mean. We cannot see the molecules, so making a model or drawing a picture will help your students to imagine what they might look like. Resource 6 contains some examples of simple formulae that you could use in order to develop your students’ understanding of the concept. When your students are working on the activity, it is important that you move around the room and listen to their conversations. You will find out a great deal about their thinking! If they have a problem, ask leading questions rather than just tell them the answer.
Case study 3: Pair work on formulas
Mrs Ogutu of Tiengre Secondary School, Kenya decided to review previous work on chemical symbols and formulas. She spent a brief moment explaining to the students that chemistry knowledge is easily communicated through use of symbols and formulas. She referred to the periodic table poster that the class had made and wrote on the board the formulas of some compounds made from the elements in the periodic table. She set the activity up as a game, asked the students to work in pairs and distributed some pebbles she had collected (she could have used plasticine instead). She told each student to secretly choose three compounds from the board and to model them using pebbles to represent the atoms. Their partner then had to work out the molecules or formulas which the models represented. She gave the students opportunities to repeat the exercise until they gained confidence in identifying the formulas of the compounds and elements.
While the students were working she moved round the classroom watching carefully what they were doing. Mrs Ogutu noticed that Sammy thought the number referred to the atom after the number so he had put water with one hydrogen and two oxygen atoms. She didn’t say anything because she wanted to see if the students could work it out for themselves, and so watched carefully. Sammy’s partner, Cornelia, was confused at first but realised what he had done. Mrs Ogutu watched as Cornelia explained formulas to Sammy. Just before the end of the lesson, she asked him to make a model of H2S and was delighted that he got it right.
Activity 3: Interpreting formulas
The aim of this activity is to reinforce what the formulas actually mean in terms of atoms.
Use formulas that your pupils need to know for the exams. Write the formulas of some elements and compounds on the board (Resource 6 has some suggestions but you could make up your own). Divide the students into pairs and tell each pupil in secret to choose one of the formulas and to draw a diagram to represent it, using circles to represent the atoms. They should then challenge their partners to identify the formula. Ask the students to repeat this several times until they are confident. At the end of the activity, gather the class round the front and ask them which ones they found difficult and what they have learnt from the activity.
You may choose to extend this to discuss how the diagrams and symbols can both be used to represent the reaction between iron and sulfur.