Materials : Metals and Non-metals - Class 8 : Notes

1. Metals:
Those materials which possess the characteristic of being hard, shiny, malleable, fusible, ductile, etc. are termed as metal. Few examples of metals are iron, gold, silver, aluminium, copper, etc.

Physical Properties of Metals:
(a) Malleability:
It is that property of metals which allows them to be beaten into the thin sheets.

Due to presence of this property, the shape of iron nail and aluminium wire can be changed on beating. The silver foils used for decorating sweets and the aluminium foil used for wrapping food are possible because of malleability property of metals.

(b) Conductivity:
It is that property of metals which allows the current and heat to pass through them easily.
Example- Metals like iron rod, nail, copper wire, etc. are good conductors of electricity.

(c) Ductility:
It is that property of metals which allows them to be drawn into the wires.Example: Metals like aluminium and copper wires are used in electric connection.

(d) Sonorous:
It is that property of metals which produces ringing sounds on hitting.

(e) Lustrous:
It is that property of metals which makes them shine and their structures are capable of reflecting incident light.

Notes: Metals like sodium and potassium are soft and can be cut with a knife. Mercury is the only metal which is found in liquid state at room temperature. These are exceptions

2. Non -Metals:
Those materials which do not possess the characteristics of metals are termed as non-metal. Materials like coal and sulphur are soft and dull in appearance. They break down into powdery mass on tapping with hammer. They are non-sonorous and are poor conductors of heat and electricity. Few examples of non metals are sulphur, carbon, oxygen etc.

Chemical Properties of Metals & Non-Metals:

1. Reaction with Oxygen
(a) For Metals:
Generally, when metals are reacted with oxygen they will form metallic oxides. And these metallic oxides are basic in nature.
Example-1: Rusting of Iron. Following is the reaction to express it.
Iron (Fe) + Oxygen (O₂) + Water (H₂O) → Iron Oxide (Fe₂O₃)Example-2: If a copper vessel is left open in presence of the moist air, then, a dull green coating will be observed on it. The green material is a mixture of copper hydroxide (Cu(OH)₂) and copper carbonate (CuCO₃). Following is the reaction to express it:
2Cu + H₂O + CO₂ + O₂→Cu (OH)₂ + CuCO₃

Testing of nature of Rusting:
(i) Collect a spoonful of rust and dissolve it in a very little amount of water.
(ii) The rust remains suspended in water. Shake the suspension well.
(iii) Test the solution with red and blue litmus papers. The red litmus turns blue.
So, generally metallic oxides are basic in nature.

(b) For Non-metals:
Generally, non-metals also produce oxides when reacted with oxygen. But, in contrast to metals, these oxides are acidic in nature.

Testing the nature of non metal:
(i) Take a small amount of powdered sulphur in a deflagrating spoon and then heat it.
(ii) As soon as sulphur starts burning, introduce the spoon into a gas jar/ glass tumbler.
(iii) Cover the tumbler with a lid to ensure that the gas produced does not escape.

(iv) After some time remove the spoon. Add a small quantity of water into the tumbler and quickly replace the lid. Shake the tumbler well. Check the solution with red and blue litmus papers.

(v) 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. Following is the reaction to express it:
Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₃)
(vi) The sulphurous acid turns blue litmus paper red.
Generally, oxides of non-metals are acidic in nature.

2. Reaction with Water:
(a) For Metals:
Some metals react vigorously with water like in case of sodium. It is stored in kerosene.. While, some metals reacts very slowly with water like in case of iron.

(b) For Non-metals:
Generally, most non-metals do not react with water but there are some non-metals which are quite reactive in air like phosphorous, which is very reactive and is kept in water to prevent explosion.

3. Reaction with Acids:
(a) For Metals:
Generally, a metal reacts with acids and releases hydrogen gas with a ‘pop’ sound.
The presence of hydrogen gas is confirmed by bringing a burning matchstick or candle near the gas. And when the burning matchstick or candle produces pop sound then it means that hydrogen gas has evoloved.
It is found that, copper does not reacts with hydrochloric acid while it reacts with a sulphuric acid.

(b) For Non-metals:
Generally, non-metals do not react with acids.

4. Reaction with Bases:
(a) For Metals:
Generally, reactions of metals with bases releases hydrogen gas, like in case of many metals they react with sodium hydroxide to produce hydrogen gas.

(b) For Non-metals:
Generally, reactions of non-metals with bases are complex.

5. Displacement Reaction:
During reaction if a metal replaces another metal from its compound then such reactions are called displacement reaction.
Metals can actually be arranged as per their reactivity order, thus, a more reactive metal will always displace a less reactive metal from its compound but a less reactive one cannot replace a more reactive metal.

Example : When zinc is reacted with copper sulphate solution, then copper will be displaced by zinc as zinc is more reactive than copper.  The blue colour of copper sulphate disappears and a powdery red mass of copper is deposited at the bottom of the beaker. The reaction-
Copper Sulphate (CuSO₄) + Zinc (Zn) → Zinc Sulphate (ZnSO₄) + Copper (Cu)

Applications of Metals:
(i) Metals are generally used in making of machines, automobiles, airplanes, cars, satellites, etc.
(ii) Some metals are used in making wires like copper, etc.
(iii) Some metals are used for making ornaments like gold, silver, etc.

Applications of Non - Metals:
(i) The oxygen necessary for all living beings to survive is a non-metal.
(ii) Some non-metals are used as fertilizers to enhance the growth of plants.
(iii) Some non-metals are used for water-purification.
(iv) Some non-metals are used as antiseptic.
(v) Non-metals used in crackers.