CBSE Class 8 Answered

Physical properties

Metals

Non-metals

Physical state

Metals are solids and heavy, except mercury and gallium which are liquid at room temperature.

Most of the non-metals are gases at room temperature. A few are solids such as sulphur and iodine. Bromine is the only non-metal which is liquid at room temperature.

Lustre

Metals in their pure state have a shining surface. This property is called metallic lustre. Metals can be polished to produce a high reflective surface.

Non-metals do not have metallic lustre because most of them are in the gaseous state. However, silicon, iodine and graphite have metallic lustre.

Hardness

Metals are generally hard, with the exception of sodium, potassium and lead which are soft and can be easily cut with a knife.

Non-metals which are solids are hard but brittle in nature. However, diamond which is an allotrope of carbon is the hardest naturally occurring substance.

Colour

Metals are grey or silver in colour, except copper which is reddish brown and gold which is yellow.

Non-metals occur in various colours. Iodine is purple, sulphur is yellow and chlorine gas is greenish yellow.

Malleability

Metals have the ability to withstand hammering and can be made into thin sheets. This property is called malleability.

Non-metals cannot be made into thin sheets by hammering, i.e. they are not malleable.

Ductility

The ability of metals to be drawn into thin wires is called ductility.

Gold and silver are the most ductile metals. It is observed that one gram of gold can be drawn into a wire with a length of 2 kilometres.

Non-metals cannot be drawn into wires, i.e. they are not ductile.

Thermal conductivity

Metals are good conductors of heat. Silver is the best conductor, followed by copper and aluminium. Because of this property, cooking vessels are made of copper and aluminium metals. Lead is a poor conductor of heat.

Non-metals do not conduct heat, except diamond and graphite, allotropes of carbon, are good conductors of heat.

Electrical conductivity

Metals are good conductors of electricity. Electrical conductivity of copper, aluminium and silver is comparatively high.

Non-metals are non-conductors of electricity. However, graphite, an isotope of carbon, is a good conductor of electricity.

Graphite is the only non-metal which is used in electrochemical cells because it is a good conductor of electricity.

Sonority

Metals produce a ringing sound when struck with a hard object. This property of metals is known as sonority, i.e. metals are sonorous.

This property is made use of for making wind chimes, metal bells etc.

Non-metals produce a dull sound when they are hit with some other material. Thus, they are non-sonorous.

Melting point and boiling point

Melting and boiling points of metals are very high. For example, melting point of iron is 1539°C. However, mercury is a metal which is liquid at room temperature and sodium, gallium and tin have low melting points.

Non-metals have low melting and boiling points, except graphite which has high melting and boiling points.