Physical Properties of Metals and Non-metals- Class 8 Science Guide

Physical Properties of Metals and Non-metals- Chemistry Guide for Class 8

Information about Physical Properties of Metals and Non-metals

Title	Physical Properties of Metals and Non-metals
Class	Class 8
Subject	Class 8 Chemistry
Topics Covered	Microorganisms causing diseases in Humans Prevention of Diseases Microorganisms causing Diseases in Animals Microorganisms causing Diseases in Plants Food Poisoning Food Preservation

Physical Properties of Metals

1. Physical State
2. Melting point and boiling point
3. Density
4. Hardness
5. Lustre
6. Malleability
7. Ductility
8. Tensile strength
9. Conductivity
10. Sonorosity

1. Physical state of Metals and Non-metals

• All metals (except mercury, which is a liquid) are solid at room temperature.
  Iron, copper, aluminium, gold and silver are some of the examples of metals.

• Non-metals (at room temperature) may exist in solid, liquid or gaseous state.
  Carbon, sulphur, phosphorus and iodine are a few examples of non-metals which exist in the solid state.
  Bromine exists as a liquid while chlorine, oxygen and nitrogen are examples of non-metals which exist in the gaseous state. 

2. Melting point and boiling point of Metals and Non-metals

• Metals generally have high melting as well as high boiling points.
  For example, melting point of iron is 1536°C and its boiling point is 3000°C.
  Some metals, however, have an exceptionally low melting point.
  For example, the melting point of caesium metal is only 28.7°C.
• Non-metals generally have low melting as well as low boiling points.
  For example, the melting point of sulphur is 119°C.
  However, there are exceptions in non-metals also. The melting point of diamond (form of carbon) is very high, i.e. 3723°C. 

3. Density of Metals and Non-metals

• Metals generally have a high density. However, there are some exceptions. Sodium and potassium, which are metals, have quite a low density. Their density value is less than that of water.
• Non-metals generally have a low density.  

4. Hardness of Metals and Non-metals

• Most metals are very hard. They can withstand quite high pressures without getting distorted.
  There are some exceptions. Sodium and potassium are metals but they are so soft that they can be easily cut with a knife or a razor blade. 
• Non-metals are generally not hard; they are brittle and easily break into pieces when hammered. 
  Diamond which is a non-metal is a form of carbon, is the hardest substance known. 

Activity 1

Take some crystals of iodine and beat them with a duster. We will observe that the crystals easily break into small pieces. 

5. Lustre of Metals and Non-metals

• Metals have a shining surface. This is known as metallic lustre.
• Non-metals generally have a dull appearance, that is, they are non-lustrous. Iodine is the only non-metal which has a natural lustre.

6. Malleability of Metals and Non-metals

• Metals are malleable, that is, they can be hammered into thin sheets without breaking. 
• Non-metals are non-malleable, that is, they cannot be hammered into sheets.
  They are brittle, and break into pieces on being hammered. 

Activity 2

Take a small piece of zinc metal (zinc granule) and strike it gently with a hammer. We observe that the zinc piece spreads a little and becomes thinner, but does not break. 

7. Ductility of Metals and Non-metals

• Metals can be drawn into thin wires. This property of metals is known as ductility.
  Copper, aluminium and iron wires are commonly used for electrical fittings, making net doors and wire meshes, and so on.
• Non-metals are non-ductile, that is, they cannot be drawn into wires.

8. Tensile strength of Metals and Non-metals

It is the property due to which a substance can bear a lot of strain without breaking.

• Metals have high tensile strength due to their ductility and malleability.
• Non-metals generally do not have high tensile strength (except carbon-fibre).

9. Conductivity of Metals and Non-metals

The ability of a material, to transfer heat energy, or electrical current, from one point to another, is taken as an indicator of its conductivity.

We generally speak of two types of conductivities:

1. Thermal conductivity
2. Electrical conductivity. 

(a) Thermal Conductivity

The thermal conductivity, of a material, is a measure of the ease with which heat energy can flow through it. 

Activity 3 

Take some hot water in a beaker and place one end of an iron rod in it. Touch the other end of the rod after sometime. What do you observe? It also becomes hot.

This activity shows that metals can easily conduct heat energy from one point to another.

• Metals are good thermal conductors. It is due to this property that metals like copper and iron are used for making cooking utensils and water boilers.

(b) Electrical Conductivity

The electrical conductivity, of a material, is a measure of the ease with which electric current can flow through it. 

Activity 4 

Connect two terminals of a battery with the two terminals of a small bulb, using copper wires as shown in the figure. What do you observe? The bulb starts glowing. This shows that copper wires readily conduct electric current from the battery to the bulb. 

• The activity shows that metals are good conductors of electricity. It is due to this property that metal wires (generally copper wires) are used in electrical fittings.
• Non-metals are generally poor conductors of heat and electricity. Most of them are non-conductors or 'insulators'.
  However, graphite, which is a form of carbon, is a good conductor of electricity; it is used in batteries.

10. Sonorosity of Metals and Non-metals

When a piece of metal is struck with something hard, a ringing sound is produced. This property of metals is known as sonorosity.

• Metals are said to be sonorous. It is due to this property that metals are used for making bells.
• Non-metals are non-sonorous. It is on the basis of these differences in their physical properties that one can distinguish metals from non-metals.

Differences between Metals and Non-metals according to physical properties

Property	Metals	Non-metals
1. Physical state	They are all solids, except mercury (which is a liquid).	They may be solid, liquid or gaseous.
2. Melting and boiling point	They generally have high melting as well as high boiling points.	They generally have low melting as well as low boiling points.
3. Density	They (generally) have a high density.	They (generally) have a low density.
4. Hardness	They are quite hard (with exceptions of sodium and potassium).	They are not hard (except diamond).
5. Lustre	They possess a natural shine.	They generally have a dull appearance.
6. Malleability and ductility	They are malleable and ductile.	They are not malleable and ductile; they are brittle.
7. Tensile strength	They have high tensile strength.	They do not have tensile strength (except carbon fibre).
8. Thermal and electrical conductivity	They are good thermal as well as good electrical conductors.	They are non-conductors or insulators (except graphite).
9. Sonorosity	They are sonorous.	They are not sonorous.

There are some elements which show some properties of metals as well as non-metals. Such elements are called metalloids. Silicon (Si), germanium (Ge), arsenic (As) are the well-known examples of metalloids.

Some Important Points

• Silver is the best conductor of heat and electricity, followed by copper and aluminium. Among metals, mercury is the poorest conductor.
• Gold and silver are highly malleable. Gold can be converted into a foil which is only 2.0 ×10^-5 mm thick.
• Gold is the most ductile metal. A two kilometre long wire can be drawn from only one gram of gold.
• On exposure to air for sometime, metals lose their shine. This is because metals react with various gases present in air and get coated with a thin layer of their oxide, carbonate or sulphide.