1. Teaching for understanding
Students have their own ideas about a topic and an effective teacher takes account of these ideas when teaching. So a good way to start teaching any topic is to find out what your students already know about the topic. You may be surprised about what they have learnt from newspapers, adults, peers, older brothers and sisters and observations. Often their ideas are not the same as the scientific ideas we want them to understand.
In this topic we will start by talking about the chemical elements and how they are the building blocks from which all other substances are made. (Resource 1 shows the periodic table with all the elements). To find out about the students’ ideas, you could ask them if they know what an element is and if they know the names of any of the common elements. They will probably have heard of iron, carbon and sulfur, but there may be others.
Case study 1 shows how one teacher helped her students to understand the definitions of elements, compounds and mixtures. Students need time to think about new words and to understand them. You will be pleased if they can remember and recite the definitions, but you need to be sure that they understand what the words really mean. That is more difficult to measure! You can use the ideas in this unit whenever you introduce new words or scientific terms. In Activity 1 we represent atoms as circles, and atoms of different elements by different coloured circles. This activity will help students understand these definitions and remember them. Organise the activity so that the students have the opportunity to talk to each other as they work out the answers. Encourage them to explain their answers to the questions.
Case study 1: Group work to probe understanding
Miss Mene had taught her Form 9 class the definitions of ‘element’, ‘mixture’ and ‘compound’, but wanted to make sure that they really understood these key ideas in chemistry. She decided to use a card-sorting activity that would give the students an opportunity to discuss their ideas. She used Resource 2 to make 12 sets of cards out of some old food packets. Each card had a diagram that represented an element, a mixture or a compound. It took quite a long time to make the cards so she persuaded her colleague who taught the next level of junior secondary to help her, and offered to share the resource with her. Miss Mene organized the students into groups of four, giving each group a set of cards. Using the information she had already given them, they had to sort the cards into three piles (elements, mixtures and compounds). Two groups then came together to check each others’ piles and discuss any differences. If they disagreed on anything they had to explain their reasons and agree on the answer.
Miss Mene found that they identified the elements, but she had to explain the difference between compounds and mixtures again.
Her colleague had to teach her class a topic on chemical reactions. She borrowed the cards to help her students revise the definitions that they had learned last year. They struggled at first, but the activity really helped them when they started the new topic on chemical reactions.
Activity 1: Think-pair-share
This activity will help you to find out whether your students understand the definitions that you have taught them.
Copy the diagrams on to the board or make one copy for each pair of students (Resource 2).
Instruct the students to work in pairs to identify which diagrams represent the elements, the compounds and the mixtures. Tell them they have to be able to explain their choices.
Next, direct each pair to compare their answers with another pair. If they disagree, they have to discuss the example with each other and agree on the right answer.
As they work, walk round and listen carefully to what they are saying. Use questioning to find out whether the students understand the reasons for their answers.
At the end of the activity you can revise the definitions and be confident that they are understood.
Section 1 : Elements, compounds and mixtures
