NCERT Class 8 Science Materials Metals And Non Metals

MATERIIALS :: METALS AND NON--METALS

4.1 Physical Properties of Metals and Non-metals

Have you ever seen a blacksmith beating an iron piece or an article made up of iron, like a spade, a shovel, an axe? Do you find a change in the shape of these articles on beating? Would you expect a You saw that the shape of the iron nail and the aluminium wire changed on beating. If they were beaten harder these could be changed into sheets. You might be familiar with silver foil used for decorating sweets. You must also be familiar with the aluminium foil used for wrapping food. The property of metals by which they can be beaten into thin sheets is called malleability. This is a characteristic property of metals. As you must have noticed, materials like coal and pencil lead do not show this property. Can we call these as metals?

Can you hold a hot metallic pan which is without a plastic or a wooden handle and not get hurt? Perhaps not! Why? Try to list some other experiences in which a wooden or plastic handle protects you from being hurt while handling hot things. On the basis of these experiences what can you say about the conduction of heat by wood and plastic? You must have seen an electrician using his screw driver. What kind of handle does it have? Why? Let us find out.You observe that iron rod, nail and copper wire are good conductors while rolled sulphur piece and coal piece are poor conductors. Where do you find the use of aluminium and copper wires? Have you seen wires of coal? Definitely not! The property of metal by which it can be drawn into wires is called ductility. Have you ever noticed the difference in sound on dropping an iron sheet/ plate, a metal coin, and a piece of coal on the floor? If not, you can try it now. Do you note any difference in the sound produced?

Have you seen wooden bells in temples? Can you give reason? The things made of metals produce ringing sound when struck hard. Suppose you have two boxes similar in appearance, one made of wood and the other of metal. Can you tell which box is made of metal by striking both the boxes? Since metals produce ringing sounds, they are said to be sonorous. The materials other than metals are not sonorous.

After performing the above activities,we can say that some materials are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity. The materials which generally posses these properties are called metals. The examples of metals are iron, copper, aluminium, calcium, magnesium, etc. In contrast, materials like coal and sulphur are soft and dull in appearance. They break down into powdery mass on tapping with hammer.  They are not sonorous and are poor conductors of heat and electricity. These materials are called non-metals. The examples of non-metals are sulphur, carbon, oxygen, phosphorus, etc.

4.2 Chemical Properties of Metals and Non-metals

A. Reaction with Oxygen You are familiar with the phenomenon  of rusting of iron. Recall the reaction by Now recall the activity of burning spoon magnesium ribbon. The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic / basic nature. Is the solution acidic or basic? How do you ascertain this? You must have observed that the red litmus turns blue. So, oxide of magnesium is also basic in nature. In general, metallic oxides are basic in nature. Let us now observe the reaction of  non-metals with oxygen. The name of the product formed in the reaction of sulphur and oxygen is sulphur dioxide gas. When sulphur dioxide is dissolved in water sulphurous acid is formed. The reaction can be given as follows:

Sulphur dioxide (SO2) + Water (H2O) → Sulphurous acid (H2SO3)

The sulphurous acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature. Recall the name of some of the laboratory acids and bases you have read in Class VII. Note down their names in Table 4.4. Identify the metal or nonmetal present in them which forms oxides with oxygen.

Exercises

1. Which of the following can be beaten into thin sheets?

(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

2. Which of the following statements is correct?

(a) All metals are ductile.

(b) All non-metals are ductile.

(c) Generally, metals are ductile.

(d) Some non-metals are ductile.

3. Fill in the blanks :

(a) Phosphorus is very non-metal.

(b) Metals are conductors of heat and .

(c) Iron is reactive than copper.

(d) Metals react with acids to produce gas.

4. Mark ‘T’ if the statement is true and ‘F’ if it is false.

(a) Generally, non-metals react with acids. ( )

(b) Sodium is a very reactive metal. ( )

(c) Copper displaces zinc from zinc sulphate solution. ( )

(d) Coal can be drawn into wires. ( )

5. Give reasons for the following :

(a) Aluminium foils are used to wrap food items.

(b) Immersion rods for heating liquids are made up of metallic substances.

(c) Copper cannot displace zinc from its salt solution.

(d) Sodium and potassium are stored in kerosene.

6. Can you store lemon pickle in an aluminium utensil? Explain.

7. What happens when

(a) Dilute sulphuric acid is poured on a copper plate?

(b) Iron nails are placed in copper sulphate solution?

Write word equations of the reactions involved.

8. Saloni took a piece of burning charcoal and collected the gas evolved in a test tube.

(a) How will she find the nature of the gas ?

(b) Write down word equations of all the reactions taking place in this process.

9. One day Reeta went to a jeweller’s shop with her mother. Her mother gave old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?

Please refer to attached file for NCERT Class 8 Science Materials-Metals And Non-Metals