These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 3 Notes – Metals and Non-metals act as excellent revision resources, particularly in preparation for board exams.
Metals and Non-metals Class 8 DAV Notes
→ Classification of Elements: Elements are broadly classified into two groups, viz. metals and non-metals. This classification is done on the basis of their physical and chemical properties.
→ Occurrence of Elements:
- Occurrence of Metals: Metals are present in the earth’s crust in abundance. Aluminium is the most abundant metal and iron is the next. Highly reactive metals are found in the form of their oxides, sulphides and carbonates, e.g. sodium, potassium, aluminium and zinc. Less reactive metals are found in their elemental or native state, e.g. gold, silver and platinum.
- Occurrence of Non-metals: Many non-metals are found in their free state in the atmosphere. Some of them also exist in the form of compounds; such as sulphides and sulphates. Mineral: A naturally occurring inorganic substance found deep under the surface of the earth is called mineral.
- Ore: A mineral from which one or more metals can be profitably extracted is called ore.
→ Metallurgy: The sequence of processes for obtaining a metal from its ore is called metallurgy. Metallurgy involves following steps:
- Concentration of ore: In this process, impurities are removed from ore.
- Reduction: In this process, ore is subjected to reduction to obtain metal in its free state,
- Refining of metal: Process of purification of metal is called refining.
→ Physical Properties:
→ Physical state of metals: All metals are solid at room temperature. Mercury is an exception as it is a liquid at room temperature.
→ Physical state of non-metals: Non-metals exist in solid, liquid and gaseous state. Carbon, sulphur, phosphorus and iodine are present as solid. Bromine is a liquid. Chlorine, oxygen and nitrogen are gases.
→ Melting point and boiling point of metals: Metals have high melting and boiling points. For example; the melting point of iron is 1536°C and its boiling point is 3000°C. Some metals are exceptions as they have low melting point, e.g. caesium’s melting point is 28.7°C.
→ Melting and boiling points of non-metals: Non-metals have low melting and boiling points. Melting point of sulphur is 119°C, but melting point of carbon is 3723°C.
→ Density: Metals usually have a high density, while non-metals have low density.
→ Hardness: Metals are usually hard. Non-metals, on the other hand, are brittle and can easily break into pieces. Sodium and potassium are metals which are so soft that they can be cut by knife. Graphite is a non-metal which is very hard.
→ Lustre: Metals have a shining surface. This property is called metallic lustre. Non-metals have dull appearance.
→ Malleability: Metals can be beaten into thin sheets. This property of metals is called malleability. Non-metals are non-malleable.
→ Ductility: Metals can be drawn into thin wires. This property of metals is called ductility. Non-metals are non-ductile.
→ Tensile Strength: Metals can bear a lot of strain without breaking. This property of metals is called tensile strength. Non-metals do not have tensile strength, but carbon fibres are exception.
→ Conductivity: Metals are good conductors of electricity and heat. Non-metals are poor conductors of heat and electricity. Graphite which is a non-metal is a good conductor of electricity.
→ Sonority: When a piece of metal is stuck with something, it produces a typical sound. This property of metal is called sonority and metals are called sonorous. Non-metals are not sonorous.
→ Metalloids: Some elements show properties of metals as well as non-metals. These are called metalloids. Silicon, germanium, arsenic, etc. are examples of metalloid.
→ Chemical Properties:
→ Reaction with oxygen: Metals react with oxygen to form metallic oxides. Metallic oxides are basic in nature:
Metal + Oxygen → Metal Oxide
When magnesium ribbon is burnt, it reacts with oxygen to make magnesium oxide.
Non-metals react with oxygen to form non-metallic oxides. Non-metallic oxides are acidic in nature.
Non metal + Oxygen → Non-metal oxide
When charcoal (carbon) is burnt, it reacts with oxygen to form carbon dioxide.
→ Reaction with water: Different metals react at different rate with water.
Sodium and potassium are highly reactive metals. They quickly react with water at normal temperature. The reaction is so vigorous that sodium and potassium catch fire on coming in contact with water. To prevent this, sodium and potassium are stored in kerosene.
Most of the metals do not react with water at room temperature. Zinc reacts with boiling water.
Iron reacts with steam. Copper, silver and gold do not react with water at any temperature.
Magnesium reacts with water on heating and forms magnesium hydroxide.
→ Reaction with acids: Most of the metals react with dilute acids to make metal salts and liberate hydrogen gas. Some metals like copper and lead do not react with dilute hydrochloric acid.
They react with sulphuric acid and nitric acid but do not liberate hydrogen gas. Platinum and gold do not react with acids at all.
Metal + Acid → Metal Salt + Hydrogen
Non-metals generally do not react with acids. Some non-metals; like sulphur and phosphorus react with hot concentrated sulphuric acid and nitric acid but they do not liberate hydrogen gas.
→ Reaction with alkalies: Metals like aluminium and zinc react with sodium hydroxide and potassium hydroxide to form salt and hydrogen gas.
→ Metal’s Reactivity Series: Metals can be arranged in a sequence on the basis of their reactivity. This series is called metal’s reactivity series.
→ Displacement Reaction: A reaction in which a more reactive metal displaces a lesser reactive metal from the aqueous solution of its salt is a type of displacement reaction.
When magnesium is added to the aqueous solution of copper sulphate, magnesium displaces copper and forms magnesium sulphate.
When iron is added to the aqueous solution of copper sulphate, iron displaces copper and forms iron sulphate.
→ Noble Metals: Some metals are least reactive. These are called noble metals, e.g. gold, silver and platinum. These metals retain their lustre for a long time. Due to this, these metals are preferred for making jewellery.
→ Uses of Metals:
- Metals are used for making cooking utensils, vessels, water boilers, toys, tools, furniture, machines, etc.
- Metals like copper and aluminium are used for making electrical wires.
- Iron is used for making bridges, buildings and machines.
- Gold, silver and platinum are used for making jewellery.
→ Uses of Non-metals:
- Nitrogen is an important plant nutrient.
- Phosphorus is used in making matchboxes.
- Iodine is used as antiseptic.
- Sulphur is used for making firecrackers, gun powder and sulphuric acid.
- Oxygen is essential for respiration in all living beings.
- Diamond is used in jewellery and in cutting and grinding tools.
- Graphite is used in batteries and pencils.
→ Pure substance: A material which is made of same kind of particles, e.g. elements and molecules.
→ Element: An element is made up of atoms of same kind.
→ Compound: A compound is made up of atoms of different kinds.
→ Metals: A substance which is hard, malleable, ductile, sonorous, good conductor of heat and electricity and has high melting and boiling point.
→ Non-Metal: A substance which is brittle, non-sonorous, bad conductor of heat and electricity and has low melting and boiling point.
→ Mineral: A naturally occurring inorganic substance which is found deep under the surface of the earth.
→ Ore: A mineral from which one or more metals can be profitably extracted.
→ Metallurgy: Sequence of procedures for extraction of metals from ore is called metallurgy.
→ Thermal conductivity: Capacity of a substance to conduct heat.
→ Electrical conductivity: Capacity of a substance to conduct electricity.
→ Uses of Alloys:
An alloy is mixture of more than two metals or a metal and non-metal. Alloys are more durable and resistant to corrosion. Alloys are used for making utensils, machines, engines, etc.
Composition and uses of alloys
|Steel||Iron + carbon||Construction material, machine parts|
|Stainless steel||Iron + chromium + nickel||Cooking utensils, surgical implements|
|Brass||Copper + zinc||Cooking utensils, decorative statues, nuts and bolts|
|Bronze||Copper + tin||Cooking utensils, coins, medals, statues|
|Duralumin||Aluminium + copper + magnesium + manganese||Aircraft bodies, automobile parts|
|German silver||Copper + zinc + nickel||Table ware|
|Alnico||Aluminium + nickel + cobalt||Magnets|
|Gun metal||Copper + tin + zinc||Gun barrels|