Materials: Metals and Non-metals
Science Class Eight
Materials and their Properties
Everything around us is called material. For example tree, water, gas, table, chair, iron, computer, bottle, shoes, etc.
There are two types of properties of materials, physical properties and chemical properties.
Physical Properties
Properties which can be observed without changing the composition of materials are called Physical Properties. The appearance, lusture, beating sound, conduction of heat and electricity, hardness, melting point, boiling point, etc. are physical properties.
Chemical Properties
Properties which can be observed in the course of reaction of materials with other material are known as Chemical Properties.
In other words how a matter or material behaves during a chemical reaction is called Chemical Properties.
The chemical properties observed during the chemical reaction of materials. Toxicity, reactivity with water, reactivity with oxygen, etc. are some examples of chemical properties of materials.
Classification of Materials: Metals and Non-Metals
Materials can be divided into two types on the basis of their physical and chemical properties; these two types of materials are Metals and Non-metals.
(a) Metals
Physical Properties of Metals
Malleability, Ductility, Hardness, Lusture, Beating sound, conductors of heat and electricity are physical properties of materials.
(1) Malleability
Metals are malleable. The property of metals by which they can be beaten into thin sheets is called Malleability.
If a material can be turned into a thin sheet after beating, then it is called metal. And this property is malleability.
(2) Ductility
The property of a metal because of which it can be drawn into a wires is called Ductility.
Thus, metals are ductile. This is the cause that wires are made of metal.
Malleability and Ductility are characteristics property of metals.
(3) Hardness
Metals are hard. For example iron, copper, alluminium, etc. are very hard. This is the cause that iron is used in making of ships, building, bridges, etc.
However, some metals are very soft and they can cut even using a knife. For example sodium is very soft metal.
(4) Physical state
All metals are solid. For example iron, copper, alluniminium, gold, silver, etc.
However mercury is only one metal which is liquid at room temperature. Mercury is exception.
(5) Lustre
Metals are shiny in appearance. This shine of metals is called Metallic Lustre. For example iron, silver, gold, copper, aluminium, etc. have shiny surface.
(6) Sonorosity
Metals produce ringing sound when beaten. This property of metal to produce ringing sound while beaten is called sonorosity. This is the cause that bells are made of metals, such as copper or iron. Because of producing ringing sound, metals are called sonorous.
(7) Conduction of electricity and heat
Metals are good conductors of electricity and heat. This is the cause that electric wires are made of metals like copper and aluminium. And cooking utensils are made of metals like aluminium, copper and iron.
(8) Melting and boiling point
Metals have high melting and boiling points. For example the melting point of iron is 1538oC and boiling point is 2862oC, melting point of copper is 1085oC and boiling point is 2562oC.
Physical Properties of Non-Metals
(1) Malleability
Non-metals are not malleable. In other words non-metals are rigid, stiff, intractable and inflexible.
When non-metals are beaten with a hammer, they are broken into pieces. For example sulphur is a non metal, and when it is beaten it is broken into pieces.
(2) Ductility
Non metals are not ductile, rather they are rigid and inflexible.
When a non metal is stretched, it is broken.
(3) Hardness
Non-metals are soft. For example sulphur, coal, phosphorous, etc. are non metals and are not hard.
However diamond which is a type of carbon and is a non-metal is the hardest natural occurring substance. Thus, diamond is exception in the group of non metal.
(4) Physical state
Non-metals are existing in the form of solid, liquid and gas all. For example, sulphur, phosphorous, etc. are solid, oxygen, hydrogen, nitrogen etc. are gases, while bromie, iodine, etc. are liquid.
(5) Lustre
Non-metals do not have shiny surface rather they are dull in appearance. For example sulphur, phosphorous, etc. are non metals and dull in appearance.
However, graphite which is a form of carbon has shiny surface and is an exception.
(6) Sonorosity
Non-metals do not produce ringing sound when beaten. Thus, non-metals are non sonorous.
(7) Conduction of electricity and heat
Non-metals are bad conductor of heat and electricity.
However graphite which is a form of carbon, a non metal, is good conductor of electricity and graphite is an exception.
(8) Melting and boiling point
Non-metals have low melting and boiling point. For example the melting point of sulphur is 115.20C.
Chemical Properties of Metals and Non-Metals
Reaction of Metals with oxygen
Metal + Oxygen ⟶ Metal Oxide
Metals like iron, copper, aluminium, magnesium, etc. reacts with oxygen and form respective oxides.
Reaction Iron with Oxygen
When iron, which is a metal, reacts with oxygen in the presence of water or water vapour present in air, it forms iron oxide. Iron oxide is red in colour and popularly known as rust of iron.
Iron (Fe) + Oxygen (O2) + Water (H2) ⟶ Iron oxide (Fe2O3)
This phenomenon is called rusting of iron.
Reaction of Magnesium with Oxygen
When magnesium ribbon is burnt in the presence of air, it forms magnesium oxide.
Magnesium (Mg) + Oxygen (O2) ⟶ Magnesium Oxide (MgO)
Reaction of Copper with oxygen
When copper metal is heated in the presence of air, it forms copper oxide.
Copper (Cu) + Oxygen (O2) ⟶ Copper oxide (CuO)
Copper oxide is black in colour.
Nature of Metal Oxides
Metal oxides are basic in nature.
(a) When magnesium oxide is dissolved in water and a red litmus paper is poured in it, the red litmus paper turns blue.
The change of red litmus to the blue, shows that, magnesium oxide is basic in nature.
(b) When rust is mix with water and a red litmus paper is poured in it, it turns blue.
Thus, rust, which is an oxide of iron is basic in nature similar to most of the other metal oxides.
Reaction of Metal with Water
Some metals forms respective hydroxide when react with water.
Metal + Water ⟶ Metal Hydroxide
Reaction of sodium metal with water
When sodium metal reacts with water, it forms sodium hydroxide.
Sodium (Na) + Water ⟶ Sodium hydroxide (NaOH)
Reaction of Potassium metal with water
When potassium metal reacts with water it forms potassium hydroxide
Potassium (K) + Water (H2) ⟶ Potassium hydroxide (KOH)
Reaction of Magnesium metal with water
Magnesium oxide is obtained when magnesium metal reacts with water.
Magnesium (Mg) + Water (H2) ⟶ Magnesium Oxide (MgO)
Reaction of Aluminium Metal with water
Aluminium does not react with cold or hot water in normal condition. Rather aluminium metal reacts with steam and aluminium oxide is formed.
Aluminium (Al) + Water (H2) ⟶ Aluminium Oxide (Al2O3)
Reaction of Iron metal with water
Iron reacts with cold or hot water very slowly. But when steam is passed over iron, iron oxide is formed.
Iron + Steam ⟶ Iron Oxide
Reaction of Lead, copper, silver and gold with water
Metals like lead, copper, silver and gold do not react with water.
But when copper is exposed to moist air for long time, a greenish thin layer is deposited over it. This greenish thin layer is the mixture of copper hydroxide and copper carbonate. This phenomenon is called tarnishing of copper.
Copper + moist air (water + carbon dioxide + oxygen) ⟶ Copper hydroxide + copper carbonate
Reaction of Metals with Acid
Metals give hydrogen gas when react with acid.
Metal + Acid ⟶ Hydrogen gas
Example
Reaction of Zinc Metal with Acid
When zinc reacts with sulphuric acid, it gives hydrogen gas and zinc sulphate.
Zinc (Zn) + Sulphuric Acid (H2SO4) ⟶ Hydrogen gas (H2) + Zinc sulphate (ZnSO4)
When a burnt matchstick is brought near the mouth of test tube in which reaction between zinc and sulphuric acid takes place, it burnt with a pop sound. This pop sound confirms the evolution of hydrogen gas, which is a characteristic test for hydrogen gas.
Reaction of Calcium Metal with Hydrochloric acid
When calcium metal reacts with hydrochloric acid, it produces hydrogen gas and calcium chloride.
Calcium (Ca) + Hydrochloric acid (HCl) ⟶ Hydrogen gas (H2) + Calcium chloride
Similarly, most of the other metals also gives hydrogen gas when react with acid.
Reaction of Copper metal with Acid
Copper metal does not react with dilute hydrochloric acid even on heating. However copper reacts with Sulphuric acid.
Reaction of Metals with Base
Metals give hydrogen gas when react with a base.
Metals + Base ⟶ Hydrogen gas
Example
Reaction of Zinc Metal with Sodium Hydroxide
When zinc metal reacts with sodium hydroxide, it gives hydrogen gas and sodium zincate.
Zinc (Zn) + Sodium hydroxide (NaOH) ⟶ Hydrogen gas (H2) + Sodium zincate
Reaction of Aluminium Metal with Sodium Hydroxide
When aluminium metal reacts with sodium hydroxide, it gives hydrogen gas and sodium aluminate.
Aluminium (Al) + Sodium hydroxide (NaOH) ⟶ Hydrogen gas (H2) + Sodium aluminate.
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