CBSE CLASS VIII NOTES ON METALS AND NON-METALS

PROPERTIES Appearance Malleability Ductility

Conductivity

Sonority

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.

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.

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

State 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.

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.

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, is a good conductor of electricity, used in dry cell.

Melting point

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.

Hardness

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

Generally soft except diamond

Other physical properties

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.

Non-metals react with oxygen and form acidic or neutral oxides.

Have significantly lower melting points and boiling points than metals (with the exception of carbon)

Sulphur reacts with oxygen to form sulphur dioxide, which is acidic.

For example, if you burn a strip of magnesium, magnesium will burn in oxygen to form magnesium oxide.

CHEMICAL PROPERTIES OF METALS

Magnesium oxide dissolves in water to form magnesium hydroxide, which is basic in nature.

Carbon monoxide and nitric oxide are neutral oxides.

Phosphorus is a very reactive nonmetal. It catches fire if exposed to air.

To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

Non-metals do not react with acids.

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

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.

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

Iron reacts with atmospheric oxygen and moisture to form iron oxide, which is commonly known as rust. Nails rust because of the moisture present in air.

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. Such metal oxides, which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.

Aluminium oxide reacts in the following manner with acids and bases –

Most metal oxides are insoluble in water but some of these dissolve in water to form alkalis. Sodium oxide and potassium oxide dissolve in water to produce alkalis as follows –

Different metals show different reactivities towards oxygen.

Metals such as 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. Iron does not burn on heating but iron filings burn vigorously when sprinkled in the flame of the burner. Copper does not burn, but the hot metal is coated with a black coloured layer of copper(II) oxide. Silver and gold do not react with oxygen even at high temperatures.

Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish.

Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. 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.

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.

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.

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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