Class 10 Metals and Non-metals

INTRODUCTION

In previous classes, you have learnt about the classification of matter on various bases. As per one of the categorization, matter can be classified into two groups, viz. metals and nonmetals. This classification is done on the basis of certain physical and chemical properties of matter. In this lesson, you will learn about metals and nonmetals. You will also learn about physical and chemical properties of metals and nonmetals. Apart from this, you will also learn about the reaction between metals and non-metals, about the occurrence of metals in nature, and about corrosion of metals. In this classification into metals and non-metals; we shall be focusing mainly on elements.

Physical Properties

Physical Properties of Metals

Metals show certain physical properties which are usually unique to metals. The key physical properties of metals are as follows:

Metallic Lustre: Metals have a typical shine which is called metallic lustre. Let us do the following actions to understand metallic lustre.

Activity:

We take pieces of iron, copper, aluminium and magnesium.

Notice the shine on each piece.
If some of the pieces do not shine, use a sandpaper to rub their surface.
You will notice lustre on each piece. Such lustre is not seen on non-metals.

Some of the metals do not lose their shine in the long run, while some others lose shine because of action of atmospheric moisture and gases. Gold, silver and platinum retain their shine for a long period. Due to this, these metals are preferred for jewellery.

Hardness: Metals are generally hard. However, some metals are soft, e.g. sodium. Let us do the following actions to understand hardness of metals.

Activity:

Take pieces of iron, aluminium, copper and sodium.

Try to cut these pieces with the help of a knife.
You won’t be able to cut the pieces of iron, aluminium or copper.
However, a piece of sodium can be easily cut with a knife.

This shows that most of the metals are hard. They cannot be cut with a knife or can be broken into pieces by a hammer. However, sodium is a soft metal which can be easily cut with a knife.

Caution: Use a pair of tongs to handle sodium. Do not touch sodium with bare hands because it is a highly reactive metal.

Malleability: A piece of metal can be beaten into a thin sheet. This property of metals is called malleability. Because of malleability, metals can be given a variety of shapes. Hence, metals are used for making various items; like cooking utensils, car body, wardrobes, jewellery, etc. Let us do the following actions to understand malleability.

Activity:

Take pieces of iron, aluminium and copper.

Take a hammer and beat the piece of iron several times at a single point. You will notice that the shape of the iron piece changes.
Repeat this step with aluminium and copper as well.
The shape of the metallic piece changes in each case. This happens because of malleability.

In fact, some metals; like gold and silver; can be made into highly thin sheets. You may have seen silver foils being used to decorate sweet dishes and other delicacies. Aluminium foils are used in many households to wrap food.

Ductility: A piece of metal can be drawn into thin wire. This property of metals is called ductility. Due to this, wires of certain metals; like copper and aluminium; can be easily made. Wires of gold are called zari which is used for making ornate patterns on garments;, especially saris and shawls.

Thermal conductivity: Metals are good conductors of heat. Due to this, cooking utensils are usually made of metals; like steel, brass, bronze, aluminium, etc. The following activity shows thermal conductivity of metals.

Activity:

Take a thick wire of any metal; like iron, aluminium or copper.

Fix this wire horizontally with a clamp and stand.
Take a thumb in and fix it at the far end of the wire with the help of wax.
Now, put a gas burner in the wire; near the clamp so that the thumb pin is far from the flame.
Heat the metallic wire for some time. Within a few minutes, the wax melts and thumb pin falls down.

This happens because heat is being conducted through the metallic wire.

Electrical conductivity: Metals are good conductors of electricity. Due to this, electric wires are made of metals. For making electrical wires, aluminium and copper are the preferred materials because they are cost effective. However, in some electrical gadgets; wires of silver or gold are used because of their superior conductivity. The following activity shows electrical conductivity of metals.

Activity:

Take a battery, a bulb, connecting wires, a switch and two clips (use with car batteries).

Make a circuit; as shown in the figure.
Take a small piece of iron and place it between two clips. Plug in the key. You will notice that the bulb glows.
Repeat the above step with pieces of different metals. The bulb glows in each case.
This shows that metals are good conductors of electricity.

Important Note: Discarded parts of a computer are processed to obtain costly metals; like gold and silver from them because their wiring contains these metals.

Sonority: When a metal is hit with something, it produces a typical bell-like sound. This property of metals is called sonority. Such a sound does not come from a non-metal. Due to this, bells are made of metals; especially of bronze and brass.
Solid State: Metals are usually available in a solid state at room temperature. Mercury is an exception as it is a liquid at room temperature. Caesium and gallium are solids but they melt when they are kept on the palm.