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PROPERTIES Appearance Malleability Ductility

METALS Metals, in their pure state, have metallic lustre (shiny). That’s why gold and silver jewellery shine so much. Some metals are malleable i.e. can be beaten into thin sheets. Gold and silver are the most malleable metals. Metals are ductile i.e. to be drawn into thin wires. Gold is the most ductile metal. A wire of about 2 km length can be drawn from one gram of gold.

Conductivity

Metals are good conductors of heat and electricity. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat. Metals are good conductors of electricity as well.

Sonority

The metals are sonorous i.e. produce a sound on striking a hard surface.

State

Melting point Hardness Other physical properties

All metals are solid in nature except Mercury (Hg). Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

Most of the metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on your palm.

NON-METALS Non metals don’t show luster(Dull) except Iodine. Non malleable Non-ductile except carbon fibres Poor conductor of heat and electricity except for graphite which is a good conductor of electricity, used in dry cell. Generally, non sonorous Non-metals exist in all the three states. Solid non-metals: Silicon and carbon Liquid non-metals: bromine Gaseous non-metals: chlorine, fluorine and oxygen Carbon, a non-metal that can exist in different forms is called an allotrope. Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon,. Have significantly lower melting points and boiling points than metals (with the exception of carbon)

Hard except sodium and potassium, these can be cut with knife

Generally soft except diamond

Metals have high density, are opaque as thin sheet, etc

transparent as thin sheet,

Almost all metals burn/combine with oxygen to form metal oxides which are basic in nature. Different metals show different reactivities towards oxygen. METAL+OXYGEN

METAL OXIDE

For example, if you burn a strip of magnesium, magnesium will burn in oxygen to form magnesium oxide. Magnesium(Mg)+Oxygen(O2)

2MgO(Magnesium)

Magnesium oxide dissolves in water to form magnesium hydroxide, which is basic in nature. Mg+2H2)O

Mg(OH2)+H2

When copper is heated in air, it combines with oxygen to form copper(II) oxide, a black oxide.

Non-metals react with oxygen and form acidic or neutral oxides. Sulphur reacts with oxygen to form sulphur dioxide(SO2), which is acidic and can dissolve in water to form sulphurous acid(H2SO3). SO2+H2O

CHEMICAL PROPERTIES OF METALS

H2SO3

When a copper vessel is exposed to moist air, a green coating/deposit forms on its surface. The coating is a mixture of copper hydroxide(Cu(OH)2) and copper carbonate (CuCO3). Cu(OH)2+CuCO3 2Cu+H 2O+CO2+O2

Carbon monoxide and nitric oxide are neutral oxides.

Iron reacts with atmospheric oxygen and moisture to form iron oxide, which is commonly known as rust(Fe2O3). Nails rust because of the moisture present in air. Iron(Fe)+Oxygen(O Fe2O3 2)+H2O

Phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

When aluminium is heated in air, it forms aluminium oxide. Most of the metal oxides are basic in nature. But some metal oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as well as basic behaviour. Potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil. At ordinary temperature, the surfaces of metals such as magnesium, aluminium, zinc, lead, etc., are covered with a thin layer of oxide. The protective oxide layer prevents the metal from further oxidation.

REACTION WITH ACIDS

Non-metals do not react with acids. The reaction of non-metals with bases is complex. For example, when chlorine reacts with a base like sodium hydroxide, it gives multiple products like sodium hypochlorite, sodium chloride and water.


Metals react with acid to liberate hydrogen gas and corresponding salt of the metals Zn+HCl

ZnCl2+H2

Zn+H2SO4

ZnSO4+H2

REACTION WITH WATER Metals react with water and produce a metal oxide and hydrogen gas. But all metals do not react with water.

Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic that the evolved hydrogen immediately catches fire.

The reaction of calcium with water is less violent. The heat evolved is not sufficient for the hydrogen to catch fire. Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. Magnesium does not react with cold water. It reacts with hot water to form magnesium hydroxide and hydrogen. It also starts floating due to the bubbles of hydrogen gas sticking to its surface. Metals like aluminium, iron and zinc do not react either with cold or hot water. But they react with steam to form the metal oxide and hydrogen.

ALLOY: An alloy is solid mixture of two or more metals or a metal and a non-metal. It is used for making coins, satellite, stainless stell, etc. Duralium has great strength and is used in aircrafts, pressure cooker, automobiles etc.

Metals such as lead, copper, silver and gold do not react with water at all Metals react with acids to give a salt and hydrogen gas. DISPLACEMENT REACTION Several metals are capable of displacing other metals from their solutions. For example; Zinc(Zn), a more reactive metal replaces copper(less reactive) from copper sulphate solution. CuSO4(Copper sulphate)+Zn(Zinc)

ZnSO4(Zinc sulphate)

Cu(Deposited as powdery red mass)

The Reactivity Series: The reactivity series is a list of metals arranged in the order of their decreasing activities.

Other chemical properties

Have 1-3 electrons in the outer shell of each metal atom, lose electrons easily, have lower electronegativities, are good reducing agents, corrode easily, etc.

Uses

Metals are used in making machinery, automobiles, aeroplanes, buildings, trains, satellites, gadgets, cooking utensils, water boilers,etc.

Usually have 4-8 electrons in their outer shell, have higher electronegativities, are good oxidizing agents, are brittle solids, readily gain or share valence electrons etc Non- metals are essential for our life which all living beings inhale during breathing Non-metals are used in fertilizers to enhance growth of plants Mon-metal are used in water purification process Some non-metals are used as an antiseptic Non-metals are sometimes used in crackers


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Cbse class viii science metals and non metals prepared by lhakpa wangyal  

Cbse class viii science metals and non metals prepared by lhakpa wangyal STRICLY BASED ON NCERT TEXTBOOK

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