Important Notes for CBSE Class 8 Science Chapter 4 – Materials Metals and Non Metals. Materials Metals and Non Metals Class 8 Notes and Study Material Download in PDF form.
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Materials Metals and Non Metals Class 8 Notes
An important classification of elements is in terms of metals and non-metals. Most of the elements are metals. The remaining are either non-metals or metalloids. Metalloids possess character of both metals and non-metals.
- Materials are mainly of two types:
1) Metals
i) Definition:These are substances characterized by high electrical and thermal conductivity. They also posses’ properties like malleability, ductility and light reflectivity.
ii) Examples:Aluminum, copper, iron, tin, gold. Around 90 naturally found elements are metals.
iii) Physical Properties:
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- Good conductors of heat and electricity
- Ductility: The property of metals by which they can be drawn into wires.
- Malleability: The property by which metals can be beaten into thin sheets is called malleability.
- Metals are sonorous. It means they produce a ringing sound when they are struck with a hard object or beaten.
- Metals are usually hard and they are lustrous or have a shiny appearance. An exception to this is Metals like sodium and potassium are soft.
- Metals are normally found in solid state except Mercury is the only metal which is found in liquid state at room temperature.
iv) Chemical properties:
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- Reaction with air: Metals react with oxygen to form basic metallic oxides. Burning of magnesium ribbon in presence of oxygen produces magnesium oxides.
- Reaction with water: Some metals react vigorously with water, Example: Sodium. There are other metals which react slowly with water, example: iron. Apart from these metallic oxidesare easily dissolved in water and form alkalis.
- Reactions with Acids: Metals are generally reactive with acids and produces hydrogen gas, more reactive metals displace the hydrogen from its dilute acid form metallic salt and hydrogen gas which makes a popping sound.
- Reactions with Bases: Some Metals react with bases. Example: 2NaOH(aq.)+Zn(s)→Na2ZnO2(aq.)+H2(g).
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Displacement reaction:
Metals have the capability to displace another less reactive metal in aqueous environment. The product of such a reaction is salt solution
Example:
i) Copper Sulphate (CuSO4) + Zinc (Zn)→Zinc Sulphate (ZnSO4) + Copper (Cu)
ii) 2Al(s)+Fe2O3(molten)→Al2O3(s)+2Fe(molten)
Uses:
- Metals are used in making heavy machinery, automobiles, Aeroplan’s, trains, satellites, industrial gadgets, cooking utensils, water boilers, etc.
- Metals are used to make electrical wires and heigh in tensile strength metal sheets.
- Aluminum foils are used in packaging medicines, cigarettes and food materials.
- Silver and gold are used to make jewelry, coins etc.
2) Non- metals
i) Definition: Non-metals are those compound’s which do not have the attributes of metals.
ii) Examples: Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine, Carbon, Sulphur, Silicon etc.
iii) Physical Properties:
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- Poor conductor of heat and electricity (except graphite) and can act as insulators.
- They are non- malleable and non-ductile.
- They are soft, brittle and appear dull i.e., they lack luster.
- They are not sonorous
- They are converted into a powder like material wen struck with a hard object
- They can occur in any state of matter viz. solid, liquid or gas
iv) Chemical properties:
- Reaction with air: Generally, oxides of non-metals are acidic in nature. Example: Sulphur dioxide (SO2) + Water (H2O) ® Sulphurous acid (H2SO3)
- Reaction with water: Generally, non-metals do not reactwith water. This is why non-metals arestored in water. An example isphosphorus is a very reactive non-metal. To prevent contact of phosphorus withatmospheric oxygen, it is stored in water.
- Reactions with acids: They do not react with acids.
- Reaction with Bases: Such reactions are complex
v) Uses:
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- Non-metal is essential for our life which all living beings inhale during breathing,
- Non-metals used in fertilizers to enhance the growth of plants.
- Non-metal used in water purification process.
- Non-metal like iodine is applied on wounds as an antiseptic.
- Non-metals used in crackers.