PHYSICAL PROPERTIES OF METALS

PHYSICAL PROPERTIES OF 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 similar change if we try to beat a piece of coal?

Let us find out.

Activity 4.1:

Take a small iron nail, a coal piece, a piece of thick aluminium wire and a pencil lead. Beat the iron nail with a hammer (Fig. 4.1). (But take care that you don’t hurt yourself in the process.) Try to hit hard. Hit hard the aluminium wire also. Then repeat the same kind of treatment on the coal piece and pencil lead. Record your observations in Table 4.2.

Figure 4.1: Beating an iron nail with hammer

Table 4.2: Malleability of Materials

Malleability.

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 metals?

Conduction

Can you hold a hot metallic pan which is without 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 screwdriver. What kind of handle does it have? Why?

Let us find out.

Activity 4.2:

Recall how to make an electric circuit to test whether electricity can pass through an object or not (Fig. 4.2). You might have performed Recall how to make an electric circuit to test whether electricity can pass through an object or not (Fig. 4.2). You might have performed

Figure 4.2: Electric tester

Table 4.3: Electrical Conductivity of Materials

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!

Ductility

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?

Sonorous

Have you seen wooden bells in temples? Can you give a reason? The things made of metals produce a 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 possess these properties are called metals. Examples of metals are iron, copper, aluminium, calcium, magnesium, etc.

Source: This topic is taken from NCERT TEXTBOOK

PHYSICAL PROPERTIES OF NON METALS

PHYSICAL PROPERTIES OF NON METALS

In contrast, materials like coal and sulphur are soft and dull in appearance. They break down into a powdery mass on tapping with a 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.

Source: This topic is taken from NCERT TEXTBOOK