Class 8 Science Chapter 4

Important Terms On Class 8 Science Chapter 4

1. Physical Properties Of Metals And Non-Metals

The first part of Class 8 Science Chapter 4 content focuses on the importance of metallurgy which is related to materials science and engineering that studies the physical and chemical behaviour of metallic elements, their inter-metallic compounds, and their mixtures. As you know, metals can be distinguished from non-metals based on their properties. Have you ever seen a blacksmith beating an iron piece like a spade, an axe or other materials? Do you find any changes in the shape of these articles on beating? Your answer will be ‘yes’. Remember, the property of metals by which they can be beaten into you thin sheets is called ‘malleability’. But materials like coal and pencil lead do not show this property.

2. Metals Are Ductile And Sonorous

Have you seen wire of coal? Your answer will be ‘no’. Generally, we see the copper wire and aluminium wire. Remember, the property of metal by which it can be drawn into wires is called ‘ductility’. Materials give a sound on beating or dropping. It is an attractive characteristic. Remember, metals produce ringing sounds; they are said to be ‘sonorous’. Thus, we can say that some materials which are hard, lustrous (gives shine), a malleable, ductile and good conductor of heat and electricity, called ‘metal’. Iron, copper, aluminium, magnesium, etc., are the example of metals. The materials which do not have the characteristics of metals called non-metals.

3. Chemical Properties Of Metals And Non-Metals

In this part of the content deals with the chemical properties of metals and non-metals. It will help you to understand what will happen if metals react with other substances, such as oxygen, water, base, acids etc. Remember, sodium metal is very reactive. It creates vigorously with oxygen and water and creates heat as iron reacts with water slowly. In the other hand, non-metals do not react with water though they may be very reactive in air. Such non-metals are stored in water.

4. Reaction Metals With Oxygen

You are familiar with the phenomenon of rusting of iron and burning of a magnesium ribbon in the air. Iron creates ferric oxides on rusting. Magnesium creates magnesium oxide on burning. The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic or basic nature. You must have observed that the red litmus paper turns blue, means it is basic in nature. Thus, we can say that metallic oxide is basic in nature. When sulphur dioxide is dissolved in water, sulphuric acid is formed. The sulphuric acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature.

5. Reaction Of Metals With Acids & Bases

If we take magnesium ribbon with hydrochloric acid for a reaction. Generally, we listen to a “Pop” sound, when a burning match stick is brought near the mouth of the test tube. If we do this type of reaction with non-metals, no “Pop-up” sound will create. Thus, it is clear that non-metals generally do not react with acids, but metals react with acids and produce ‘hydrogen gas’ that burns with a “Pop sound”. As you learn before, the pop sound indicates the presence of hydrogen gas. Metals react with Sodium Hydroxide to produce hydrogen gas. While the reaction of non-metals with bases are complex.

6. Displacement Reaction

In this part of Class 8 Science the content gives you an idea about the reactivity of different materials which helps you to understand the concept of stronger element and weaker element with their reactions. Do you know that when a more reactive metal is placed in the salt solution of all less reactive metal, then the more reactive metal displaces the less reactive metal from its salt solution? This is known as the displacement reaction. Remember, a stronger reactive metal can always displace a less reactive metal, but a less reactive cannot replace a more reactive-metals.
When zinc is reacted with copper sulphate solution, then the copper will be displaced by zinc as zinc is more reactive than copper. Similarly, when a strip of iron metal is placed in a copper sulphate solution for sometimes, then the blue colour of copper sulphate solution fades and read brown coating of copper metal is deposited on the iron strip. The solution turns green is due to the formation of iron sulphate where a more reactive metal ion is displacing a less reactive metal copper from its salt solution that means copper sulphate solution.

7. Uses Of Metals And Non-Metals

In this part of the chapter teaches the uses of metals and non-metals in various industries. Metals are generally used in making machinery, automobiles, aeroplane, trains, satellites, modern gadgets, cooking utensils, water boilers etc. Some costly metal is used for making ornaments like gold, silver, platinum etc. You are also familiar with the uses of some non-metals. Oxygen is important for the survival of all living beings. Remember, oxygen is non-metal. Some non-metals like nitrogen, phosphorus are used as fertilizer to enhance the growth of the plants. Non-metals, like chlorine, is used in the water purification process. Non-metals such as sulphur is used in crackers also. In this way, you can see the importance of metals and non-metals with their physical and chemical properties. So, keeping these concepts in mind.