ETV “Junior Secondary Science” Programme

“Elements and Compounds”

Teachers’ Notes

Target Audience

Secondary 1 - 3

Duration

20 minutes

Production Aim

This programme is a teaching resource produced especially for enriching the classroom teaching of the Syllabus for Science (Secondary 1 – 3) prepared by the Curriculum Development Council (1998).

The content of the programme serves to illustrate the following parts of the Syllabus:

“Unit 13: Metals-

13.2 ‘How to obtain metals’”

Key Points

  1. An introduction to types,names and symbols of elements;
  2. An explanation of the formation of compounds and their nature;
  3. An explanation ofchemical change and physical change.

Content Outline

This programme is divisible into 3 parts as follows:

  1. Elements

-Classification of Elements: according to their different states, elements can be classified as solid, liquid and gas. Besides, elements can also be classified as metal and non-metal.

-Nature of metal element: the surface is usually glossy and it can be rolled into thin sheet or stretched into thread. When heated, it becomes softened and its shape changes, sometimes it can even be melted into liquid form. Metal element is a good conductor for heat and electricity.

-Nature of non-metal element: the surface is usually matt with low hardness. Apart from graphite, non-metal elements cannot conduct electricity.

-Symbols of elements: scientists use different alphabets to represent different elements.

-Elements are formed by atoms: The programme uses animation to explain the structure of atoms. Atom normally composes of proton, nucleus and electrons. Animation is used to explain the structure of different atoms and the meaning of different numbers of protons in a particular atom. Different number of protons represents different atoms. Elements are made up of atoms while the compositionof atoms varied. Examples like hydrogen, oxygen, nitrogen, calcium and sodium are given to illustrate the point.

  1. Compounds

-It is the fact that a lot of things in the world are compounds, which are made up of two or more elements. Experiments are conducted to illustrate the nature of sodium, chlorine and sodium chloride to point out that the compound sodium chloride is very much different in nature from the component elements sodium and chlorine.

-Besides sodium chloride, experiments are also conducted to illustrate the reaction of oxygen and magnesium to become magnesium oxide, as well as the reaction of iron and sulphur to become iron sulphide. These experiments show that compoundsare much different in nature from their component elements.

  1. Chemical Change and Physical Change

-Use the formation of sodium chloride, magnesium oxide and iron sulphide to explain the idea of chemical change and introduce the terms like reactantsproducts.

-Point out the fact that chemical change usually involves obvious change in energy. Besides, chemical change is comparatively more difficult to reverse.

-Explain physical change by illustrations like heating water to become steam, breaking glass on the floor and dissolving sugar cube in water. Point out the fact that in physical change, there is no formation of new product of different chemical property.

Suggestions for Utilization

The teacher can screen the programme in whole or in parts according to actual needs. The teacher may spend 5 to 10 minutes at the beginning of each lesson to lead students to discuss with reference to the Preparation before viewing the programme part of the Suggested Activities. The teacher may then show the programme. After the show, the teacher may spend another 10 to 15 minutes to discuss with students with a view to consolidating the concepts and methods illustrated in the programme. The teacher is advised to refer to the Activities after viewing the programme part of Suggested Activities.

Suggested Activities

(The following activities are suggested for teacher’s reference only. The teacher may wish to use the activities according to students’ abilities, the learning environment of the class, and the teaching time available.)

Preparation before viewing the programme

The teacher may demonstrate the experiment of electrolyzing water (slightly acidified) to get hydrogen and oxygen as a lead-in. Students are then required to discuss the relationship between water, hydrogen and oxygen.

Activities after viewing the programme

-Students may study the names of some compounds and then point out whichelementsthey are composed of.

-The teacher may instruct students to conduct the following activities and ask them to point out whether the change involved is chemical change or physical change.

  1. grinding chalk into powder
  2. mixing tea and coffee
  3. frying an egg
  4. burning a piece of paper

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