Question

write a long explanation of chapter metals and non metals . in detail and also according to class 8

Answer 1

◆ Metals And Non- Metals ◆
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There are more than one hundred elements known so far . The earliest Non- Metals known to man are carbon and sulphur . Some of these elements can be classified according to their behavior.

On the basis of their properties All the elements can be divided into two main groups:-

→ Metals And
→ Non - Metals.

But there are also certain elements which have some properties of Metals and some of Non- metals. They are known as Metalloids Such as Antimony, Arsenic, and tellurium. Metals and Non- Metals are used for making tools, Machines, Automobiles like cars, buses, houses, jewellery, utensils, etc.

On the basis of chemical reaction metals are the elements Which form positive ions by loosing electrons. Non- Metals are the elements which form negative ions by gaining electrons . The noble gas does not form ions so cannot be classified as Metal or Non-Metal.

PHYSICAL PROPERTIES OF METALS AND NON- METALS :
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Various physical properties which enables us to distinguish metals from non- metals : -

♣ State :

All metals are solid at room temperature. only Mercury is a metal in liquid form.

♣ Colour :

Metals usually have a silver or grey colour.

♣ Metallic lustre :

Metals in the pure state generally shine and can be polished . The shine on the metallic surface is called the metallic lustre.

♣ Hardness :

Metals are generally hard like iron except some which are soft like Pottassium and sodium and can be cut with a knife.

♣ Density :

Metals have high densities. The density of a Substance is a measure of how heavy it is .

Density = Mass ( in g ) / volume ( in cm³ )

According to density , metals are divided into two groups — light metals and heavy metals . Metals like Sodium and pottasium are so light that they can even float on water.

♣ Malleability :

Some metals can be beaten into thin sheets with hammer without breaking . This property of metals is called malleability. Gold and silver are the most malleable metals. They can be hammered into very thin sheets. Silver foils are used for decorating sweets. Aluminum foils are used for wrapping of medicines , chocolates , etc.

♣ Ductility :

Ductility is the property by virtue of which metals can be drawn into wire. Gold and Silver are the best ductile metals. Copper and Aluminium are also drawn into wire and used in electrical wiring.

♣ Conductivity :

All metals conduct heat and electricity. Three very good conductors of electricity are silver , copper and aluminum. Silver is used for electrical contacts in computer. Mercury is worst conductor of heat.

♣ Sonority :

Metals are generally sonorous . They make a singing sound when we strike them. Therefore, they are used for making bells and metals wires being used in musical instruments such as Sitar and guitar.

♣ Melting and Boiling point :

Metals have generally high melting points and Boiling points. However, sodium and potassium have low melting points.

◆ Some physical properties of Non-Metals are :-

♠ Physical Properties :

Three Physical states of matter in which non- metal exist are solid , liquid, and gas . The Physical properties of Non-Metals are opposite to that of metals.

Example :- carbon, sulphur, Phosphorous, etc. are solid non- metals. Bromine is liquid non-metal; oxygen , Hydrogen, nitrogen etc. are gasesous non- metals .

♠ Lustre :

Non- metals do not have lustre. They have dull appearance. But some exceptions as Graphite, diamond and iodine have Crystal shine.

♠ Malleability :

Non- metals are non-melleable that is they cannot be beaten into thin sheets.

♠ Ductility :

Non- metals are non- ductile . They cannot be drawn into wires.

♠ Conductivity :

Non metals are poor conductors of heat and electricity except Graphite which is a good conductor of electricity and heat.

♠ Melting points :

Non- metals usually have low melting points.

♠ Hardness :

Non- metals are usually soft except diamond which is the hardest known non-metal. Non- metals are brittle, when hammered they break into pieces.

♠ Sonorous :

Non- metals are non- Sonorous.

◆ Noble Metals :-
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Some metals remain unaffected in Air, water , acidic Solution or alkaline solution and are found in free state . They are chemically unreactive. They are known as" Noble Metals or " Inert metals". Gold, Silver and platinum are noble metals. and they have metallic Lustre for long time.

◆ Alloys :-
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An alloy is a metallic material composed of two or more metals or one or more metals and Non-Metals. Alloying can be used to increase Hardness of Metals . It takes metals more resistant to attack by chemicals and atmospheric corrosion. It can change the properties of Metals in other ways .

◆ Corrosion of Metals :-
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Iron gets oxidised to iron oxide (Fe2O3)(reddish Brown) By the action of atmospheric oxygen in the presence of moisture.

4Fe + 3O2 + 3H2O → Fe2O3 + 2Fe(OH)3 } RUST

Answer 2

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CHEMICAL PROPERTIES OF METALS AND NON-METALS :
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Metals and Non- Metals have certain Chemical properties .

♣ Reaction Of Metals With Oxygen :

Metals react with Oxygen to form metal Oxides which are called metallic or basic Oxides. The Oxides are basic in nature, that turn red litmus paper blue.

Example :- Magnesium ribbon (metal) on heating in air or Oxygen catches fire and burns with white flame to form Magnesium oxide.

Metal + Oxygen → Metal Oxide

2Mg + O2 → 2 Mgo
Magnesium + Oxygen → Magnesium oxide

4Na + O2 → 2 Na2O
Sodium + Oxygen → Sodium Oxide

2Zn + O2 → 2 ZnO
Zinc + Oxygen → Zinc Oxide

Aluminum on reaction with Oxygen forms aluminum Oxide which covers it's surface and acts as a protective layer to prevent further Oxidation.

♣ Reaction Of Metals With Water :

Sodium reacts vigorously with water while other metals do not do so.

◆ They dissolve in water to form alkalies . when metals react with water they form metal oxide or metal hydroxide and hydrogen gas is evolved.

Metal + H2O → Metal Oxide + Hydrogen Gas or Metal hydroxide.

2Na + 2H2O → 2NaOH + H2 ↑
Sodium + Water → Sodium hydroxide + hydrogen.

2K + 2H2O → 2KOH + H2 ↑
Potassium + Water → potassium Hydroxide + hydrogen.

◆ The reaction of calcium with cold water is not violent . It takes place slowly.

Ca + 2H2O → Ca(OH)2 + H2 ↑
Calcium + Water → Calcium hydroxide + Hydrogen.

◆ Magnesium hardly reacts with cold water. Reaction is faster with hot water and is vigorous with stream.

Mg + 2H2O → Mg(OH)2 + H2 ↑
Magnesium + Steam → Magnesium hydroxide + Hydrogen.

Mg + H2O(g) → MgO + H2 ↑
Magnesium + Steam → Magnesium Oxide + Hydrogen.

◆ Metals like aluminum , Zinc and iron do not react with cold water or hot water. They react with Steam but reaction is very slow.

2Al + 3H2O(g) → Al2O3 + 3H2(g)
Aluminium + Steam → Aluminium oxide + Hydrogen.

Zn + H2O(g) → ZnO + H2(g)
Zinc + Steam → Zinc Oxide + Hydrogen

3Fe + 4H2O(g) → Fe3O4 + 4H2(g)
Iron + Steam → Ferric Oxide + Hydrogen

◆ Metals like Copper, Silver and Gold do not react with water.

♣ Reaction Of Metals With Acids :

Metals react with acids to form Salts and liberate hydrogen gas.

Metal + Acid​ → Salt + Hydrogen

2Na + 2HCI(dil) → 2NaCl + H2(g)
Sodium + Hydrochloric Acid (dil) → Sodium Chloride + Hydrogen

Mg + H2SO4 → MgSO4 + H2(g)
Magnesium + Sulphuric Acid → Magnesium sulphate + Hydrogen

Fe + 2HCl(dil) → FeCl2 + H2(g)
Iron + Hydrochloric Acid(dil) → Ferrous Chloride + Hydrogen

♣ Reaction Of Metals With Bases :

Mostly Metals do not react with bases . Some metals like lead, Zinc, Aluminium react with strong bases only and produce Compound of metal and hydrogen gas.
Copper, Silver and Gold do not react with acids.

♣ Displacement Reaction :

A Chemical reaction that takes place when an element replaces another element in a compound is known as Displacement Reaction.

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Chemical Properties Of Non-Metals :-

♣ Reaction of Non-Metals With Oxygen :

Non- Metals reacts with Oxygen to form neutral oxides or acidic oxides . The acidic oxides when dissolved in water they form acids , which turns blue litmus paper red.

Examples :

◆ C + O2 → CO2
Carbon + Oxygen → Carbon dioxide

CO2 + H2O → H2CO3
Carbon dioxide + Water → Carbonic Acid

◆ S + O2 → SO2
Sulphur + Oxygen → Sulphuric Dioxide

SO2 + H2O → H2SO3
Sulphur dioxide + Water → Sulphurous Acid

◆ N2 + 2O2 → 2NO2
Nitrogen + Oxygen → Nitrogen dioxide

NO3 + H2O → HNO3
Nitrogen Dioxide + water → Nitric Acid

♣ Reaction Of Non-Metals With Water :

Non-Metals do not react with water or steam to evolve hydrogen gas. Phosphorous is very reactive if Kept in open air , it catches fire when combines with O2 from air.

♣ Reaction Of Non-Metals With Acids :

Non-Metals do not react with dilute acids. But sulphur reacts with hot concentrated nitric acid to produce sulphur dioxide , nitrogen dioxide and water. No Hydrogen gas is evolved.

S + 4HNO3 → SO2 + 4NO2 + 2H2O
Sulphur + Nitric Acid → Sulphur dioxide + Nitrogen dioxide + water.