8 materials - metals and non-metals

MATERIALS : METALS AND NON-METALSMATERIALS : METALS AND NON-METALS

You are familiar with a number ofmaterials like iron, aluminium,copper, etc. Some materials have

been given in Table 4.1.

similar change if we try to beat awood log ?

Let us find out.

Activity 4.1

Take a small iron nail, a coal piece,a piece of thick aluminium wire anda pencil lead. Beat the iron nail witha hammer (Fig. 4.1). (But take carethat you don’t hurt yourself in theprocess). Try to hit hard. Hit hard

Table 4.1 : Appearance andHardness of materials

Object Appearance Hardness/Material (Shiny/Dull) (Very hard/

Not veryhard)

Iron

Coal

Sulphur

Aluminium

Copper

-----

Can you name the materials whichare metals? The rest of the materials inTable 4.1 are non-metals. Metals can bedistinguished from non-metals on thebasis of their physical and chemicalproperties. Recall that lustre andhardness are physical properties.

4.1 Physical Properties ofMetals and Non-metals

Have you ever seen a blacksmith beatingan iron piece or an article made up ofiron, like a spade, a shovel, an axe? Doyou find a change in the shape of thesearticles on beating? Would you expect a

Table 4.2 Malleability of Materials

Object/ Change in ShapeMaterial (Flattens/Breaks

into pieces)Iron nail

Coal piece

Aluminium wire

Pencil lead

also the aluminium wire. Thenrepeat the same kind of treatmenton the coal piece and pencillead. Record your observations inTable 4.2.

Fig. 4.1 : Beating an iron nail with hammer

Fig. 4.2 : Electric tester

Where do you find the use ofaluminium and copper wires? Have youseen wires of coal? Definitely not!

The property of metal by which it canbe drawn into wires is called ductility.

Have you ever noticed the differencein sound on dropping an iron sheet/plate, a metal coin, and a piece of coalon the floor? If not, you can try it now.

Do you note any difference in the soundproduced?

Oh! The meaning of recallingour experiences and then of

this activity was to show thatmetals are good conductors ofheat and electricity. We learnt

this in Class VI.

MATERIALS : METALS AND NON-METALS 45

You saw that the shape of the iron nailand the aluminium wire changed onbeating. If they were beaten harder thesecould be changed into sheets. You mightbe familiar with silver foil used fordecorating sweets. You must also befamiliar with the aluminium foil used forwrapping food. The property of metals bywhich they can be beaten into thin sheetsis called malleability. This is acharacteristic property of metals. As youmust have noticed, materials like coal andpencil lead do not show this property. Canwe call these as metals?

Can you hold a hot metallic pan whichis without a plastic or a wooden handleand not get hurt? Perhaps not! Why? Tryto list some other experiences in which awooden or plastic handle protects youfrom being hurt while handling hotthings. On the basis of these experienceswhat can you say about the conductionof heat by wood and plastic?

You must have seen an electricianusing his screw driver. What kind ofhandle does it have? Why?

Let us find out.

Activity 4.2

Recall how to make an electriccircuit to test whether electricity canpass through an object or not(Fig. 4.2). You might have performed

the activity with various objects inClass VI. Now, repeat the activitywith the materials mentioned inTable 4.3. Observe and group thesematerials into good conductors andpoor conductors.

Table 4.3 : Electricalconductivity of materials

S.No. Materials Good Conductor /PoorConductor

1. Iron rod/nail

2. Sulphur

3. Coal piece

4. Copper wire

You observe that iron rod, nail andcopper wire are good conductors whilerolled sulphur piece and coal piece arepoor conductors.

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Have you seen wooden bells intemples? Can you give reason?

The things made of metals produceringing sound when struck hard.Suppose you have two boxes similar inappearance, one made of wood and theother of metal. Can you tell which boxis made of metal by striking both theboxes?

Since metals produce ringingsounds, they are said to be sonorous.The materials other than metals are notsonorous.

After performing the above activities,we can say that some materials are hard,lustrous, malleable, ductile, sonorousand good conductors of heat andelectricity. The materials whichgenerally posses these properties arecalled metals. The examples of metalsare iron, copper, aluminium, calcium,magnesium, etc. In contrast, materialslike coal and sulphur are soft and dullin appearance. They break down intopowdery mass on tapping with hammer.They are not sonorous and are poorconductors of heat and electricity. Thesematerials are called non-metals. Theexamples of non-metals are sulphur,carbon, oxygen, phosphorus, etc.

which rust is formed. You had alsoperformed in Class VII an activity ofburning a magnesium ribbon in air. Youhad learnt that in both the processesoxide formation takes place. Completethe following reactions of iron andmagnesium with oxygen.

Iron (Fe) + Oxygen (O2) + Water (H2O) → ?Magnesium (Mg) + Oxygen (O2) → ?

Activity 4.3

Let us check the nature of rustformed as a result of the reactionbetween iron, oxygen and water.Collect a spoonful of rust anddissolve it in a very little amount ofwater. You will find that the rustremains suspended in water. Shakethe suspension well. Test thesolution with red and blue litmuspapers (Fig. 4.3). What do youobserve? Is the solution acidic orbasic?

Metals like sodium and potassium aresoft and can be cut with a knife.Mercury is the only metal which isfound in liquid state at roomtemperature. These are exceptions.

4.2 Chemical Properties ofMetals and Non-metals

A. Reaction with Oxygen

You are familiar with the phenomenonof rusting of iron. Recall the reaction by

Rust

Rustsuspension

Red litmuspaper

Fig. 4.3 : Testing the nature of rust


Fig. 4.4 (a) : Burning of sulphur powder

Improviseddeflagrating

spoonNow recall the activity of burningmagnesium ribbon. The ash obtainedon burning magnesium ribbon isdissolved in water and tested for itsacidic / basic nature.

Is the solution acidic or basic? Howdo you ascertain this?

You must have observed that the redlitmus turns blue. So, oxide of magnesiumis also basic in nature. In general, metallicoxides are basic in nature.

Let us now observe the reaction ofnon-metals with oxygen.

Activity 4.4

(To be demonstrated by the teacherin the class)

Take a small amount of powderedsulphur in a deflagrating spoon andheat it. If deflagrating spoon is notavailable, you may take a metallic capof any bottle and wrap a metallic wirearound it and give it the shapeshown in Fig. 4.4 (a).

As soon as sulphur starts burning,introduce the spoon into a gas jar/glass tumbler [Fig. 4.4 (a)]. Cover thetumbler with a lid to ensure thatthe gas produced does not escape.Remove the spoon after some time.Add a small quantity of water intothe tumbler and quickly replace thelid. Shake the tumbler well. Checkthe solution with red and bluelitmus papers [Fig. 4.4 (b)].

When a copper vessel is exposed tomoist air for long, it acquires a dullgreen coating. The green material isa mixture of copper hydroxide(Cu(OH)2) and copper carbonate(CuCO3). The following is the reaction2Cu+H2O+CO2+O2→Cu (OH)2 + CuCO3

moist air

Does copper also getrusted? I have seena greenish depositon the surface ofcopper vessels.

Fig. 4.4 (b) : Testing of solution with litmuspapers

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The name of the product formed inthe reaction of sulphur and oxygen issulphur dioxide gas. When sulphurdioxide is dissolved in water sulphurousacid is formed. The reaction can be givenas follows:

Sulphur dioxide (SO2) + Water (H2O) →Sulphurous acid (H2SO3)

The sulphurous acid turns bluelitmus paper red. Generally, oxides ofnon-metals are acidic in nature.

Recall the name of some of thelaboratory acids and bases you have readin Class VII. Note down their names inTable 4.4. Identify the metal or non-metal present in them which formsoxides with oxygen.

B. Reaction with Water

Let us see how metals and non-metalsreact with water.

Table 4.4 : Metals and Non-metals in Acids and Bases

S.No. Name of the base Metal Name of the acid Non-metal

1. Calcium hydroxide Calcium Sulphuric acid Sulphur

2.

3.

4.

5.

Sodium metal is very reactive. Itreacts vigorously with oxygen andwater. A lot of heat is generated inthe reaction. It is, therefore, storedin kerosene.

Activity 4.5

To be demonstrated by the teacher.During demonstration special careshould be taken that the size of thesodium metal piece is roughly thesize of a wheat grain. It should beheld with a pair of tongs.)Take a 250 mL beaker/glass tumbler.Fill half of it with water. Nowcarefully cut a small piece of sodiummetal. Dry it using filter paper andwrap it in a small piece of cotton.Put the sodium piece wrapped incotton into the beaker. Observecarefully. During observation keepaway from the beaker. When reactionstops touch the beaker. What do youfeel? Has the beaker become hot?Test the solution with red and bluelitmus papers. Is the solution acidicor basic?

Fig. 4.5 : Reaction of sodium with water


You observed that sodium reactsvigorously with water. Some other metalsdo not do so. For example, iron reactswith water slowly.

Generally, non-metals do not reactwith water though they may be veryreactive in air. Such non-metals arestored in water. For example,phosphorus is a very reactive non-metal.It catches fire if exposed to air. To preventthe contact of phosphorus withatmospheric oxygen, it is stored in water.

C. Reactions with Acids

Let us see how metals and non-metalsbehave with acids.

Activity 4.6

Warning : Keep the mouth of thetest tube away from your face. Usetest tube holder to hold the testtube.Take samples of metals and non-metals listed in Table 4.5 in separate

Table 4.5 : Reaction of metals and non-metals with acids

Test Metal/ Reaction with dilute Reaction with dilutetube Non-Metal Hydrochloric acid Sulphuric acidLabel room warm room warm

temperature temperature

A Magnesium

(ribbon)

B Aluminium (foil)

C Iron (filings)

D Copper (peeled

flexible wire)

E Charcoal (powder)

F Sulphur (powder)

test tubes and label them as A, B,C, D, E, and F. With the help of adropper add 5 mL of dilutehydrochloric acid to each test tubeone by one. Observe the reactionscarefully. If no reaction occurs in acold solution, warm the test tubegently. Bring a burning matchsticknear the mouth of each test tube.Repeat the same activity usingdilute sulphuric acid instead of thedilute hydrocholoric acid. Recordyour observations in Table 4.5.

Is there a difference in the way metalsand non-metals react with acids? Whatcould the ‘pop’ sound in some cases bedue to when a burning match stick isbrought near the mouth of the testtubes?

You must have found that non-metals generally do not react with acidsbut metals react with acids and producehydrogen gas that burns with a ‘pop’sound. You must have noticed that

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Cu Cu

No Change

ZnSO4 FeSO4

copper does not react with dilutehydrochloric acid even on heating butit reacts with sulphuric acid.

D. Reactions with Bases

Activity 4.7

To be demonstrated by the teacher.During the preparation of sodiumhydroxide solution, care should betaken that pellets of sodiumhydroxide are handled with aplastic spatula.

Prepare a fresh solution of sodiumhydroxide in a test tube bydissolving 3-4 pellets of it in 5 mLof water. Drop a piece of aluminiumfoil into it. Bring a burning matchstick near the mouth of the testtube. Observe carefully.

What does the ‘pop’ sound indicate?As before, the ‘pop’ sound indicates thepresence of hydrogen gas.

Metals react with sodium hydroxideto produce hydrogen gas.

Reactions of non-metals with basesare complex.

E. Displacement Reactions

Recall the activity of the reaction betweencopper sulphate and iron that youperformed in Class VII. Let us observesome more reactions of that kind.

Activity 4.8

Take five 100 mL beakers and labelthem A, B, C, D and E. Take about50 mL of water in each beaker.Dissolve in each beaker ateaspoonful of each substance asindicated in Fig. 4.6 (a).

(a)

Beaker A : Copper sulphate (CuSO4) + Zinc granule (Zn),

Beaker B : Copper sulphate (CuSO4) + Iron nail (Fe)

Beaker C : Zinc sulphate (ZnSO4) + Copper turnings (Cu),

Beaker D : Iron sulphate (FeSO4) + Copper turnings (Cu)

Beaker E : Zinc sulphate (ZnSO4) + Iron nail (Fe)

Fig. 4.6 (a) and (b) : Displacement reactions

A B C D E

A B C D E

(b)


replace copper in beaker ‘A’ why cannotcopper replace zinc in beaker ‘C’?Remember that science is not arbitrary.It follows definite rules based on facts.And the rule here is that zinc is morereactive than copper and iron. A morereactive metal can replace a less reactivemetal, but a less reactive one cannotreplace a more reactive metal. Now youcan understand why there are nodisplacement reactions in beakers Dand E also. Can you guess thesequence of metals from more reactiveto less reactive among zinc, iron andcopper?

4.3 Uses of Metals and Non-metals

You should be able to guess why metalsare used in making machinery,automobiles, aeroplanes, trains,satellites, industrial gadgets, cookingutensils, water boilers, etc. You are alsofamiliar with the uses of some non-metals. Here are some interesting ones.We are sure that you will guess themright:� Non-metal essential for our life which

all living beings inhale duringbreathing,

� Non-metals used in fertilisers toenhance the growth of plants,

� Non-metal used in water purificationprocess,

� Non-metal used in the purplecoloured solution which is appliedon wounds as an antiseptic,

� Non-metals used in crackers.

You may add some more uses ofmetals and non-metals from yourexperiences.

� Keep the beakers undisturbed forsome time.

� Record your observations in yournote book.

What changes do you observe in thevarious beakers? You have read that onemetal displaces another metal from itscompound in aqueous solution. Inbeaker ‘A’ zinc (Zn) replaces copper (Cu)from copper sulphate (CuSO4). That iswhy the blue colour of copper sulphatedisappears and a powdery red mass ofcopper is deposited at the bottom of thebeaker. The reaction can be representedas follows:

Copper Sulphate (CuSO4) + Zinc (Zn) (Blue)→ Zinc Sulphate (ZnSO4) + Copper (Cu)

(Colourless) (Red)

You can write down the reactiontaking place in beaker ‘B’ in a similarmanner.

I have understood the reactionstaking place in beakers ‘A’ and‘B’. But I am still confused whythere is no change in beakers

‘C’, ‘D’ and ‘E’?

There could have been displacementof zinc by copper in beaker ‘C’ and byiron in beaker ‘E’. Similarly iron couldbe displaced by copper in beaker ‘D’.

Since we do not see any change inbeaker C, we can infer that copper isnot able to replace zinc from zincsulphate. But why? When zinc can

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I heard that magnesium isfound in plants. In whatform is it found in them?

Doctor reported irondeficiency in my body.

Where is iron in my body?

In Class VII, you have learnt that in a chemical reaction, new substances are formed.These substances are different from those which underwent the reaction. Now, if asubstance cannot be broken down further by chemical reactions, by cooling, heating,or by electrolysis, it is called ‘element’. Sulphur is an element. So is iron. Carbon, too,is an element. The smallest unit of an element is atom. A sample of an elementcontains only one kind of atoms. The atom of an element remains unaffected by physicalchanges in the element. For example, an atom of liquid sulphur would be exactly thesame as the atom of solid or vapour sulphur.

Although we have an infinite variety of substances in the universe, the number ofelements forming these substances is limited. There are no more than 92 naturallyoccurring elements. An important classification of elements is in terms of metals andnon-metals. Most of the elements are metals. Less than 20 are non-metals. A few aremetalloids which possess characters of both metals and non-metals.


KEYWORDS

ATOM

CONDUCTOR

DISPLACEMENT

REACTION

DUCTILITY

ELEMENTS

HARDNESS

MALLEABILITY

METALS

METALLOIDS

NON-METALS

SONOROUS

WHAT YOU HAVE LEARNT

� Metals are lustrous whereas non-metals have

no lustre.

� Generally, metals are malleable and ductile.

Non-metals do not have these properties.

� Generally, metals are good conductors of heat

and electricity but non-metals are poor

conductors.

� On burning, metals react with oxygen to

produce metal oxides which are basic in

nature. Non-metals react with oxygen to

produce non- metallic oxides which are acidic

in nature.

� Some metals react with water to produce metal

hydroxides and hydrogen gas. Generally, non-

metals do not react with water.

� Metals react with acids and produce metal

salts and hydrogen gas. Generally, non-metals

do not react with acids.

� Some metals react with bases to produce

hydrogen gas.

� More reactive metals displace less reactive

metals from their compounds in aqueous

solutions.

� Metals and non-metals are used widely in

every day life.

Exercises

1. Which of the following can be beaten into thin sheets?

(a) Zinc (b) Phosphorus (c) Sulphur (d) Oxygen

2. Which of the following statements is correct?

(a) All metals are ductile.

(b) All non-metals are ductile.

(c) Generally, metals are ductile.

(d) Some non-metals are ductile.

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E X

E R

C I

S E

S

3. Fill in the blanks :

(a) Phosphorus is very non-metal.

(b) Metals are conductors of heat and .

(c) Iron is reactive than copper.

(d) Metals react with acids to produce gas.

4. Mark ‘T’ if the statement is true and ‘F’ if it is false.

(a) Generally, non-metals react with acids. ( )

(b) Sodium is a very reactive metal. ( )

(c) Copper displaces zinc from zinc sulphate solution. ( )

(d) Coal can be drawn into wires. ( )

5. Some properties are listed in the following Table. Distinguish betweenmetals and non-metals on the basis of these properties.

Properties Metals Non-metals

1. Appearance

2. Hardness

3. Malleability

4. Ductility

5. Heat Conduction

6. Conduction of Electricity

6. Give reasons for the following :

(a) Aluminium foils are used to wrap food items.(b) Immersion rods for heating liquids are made up of metallic substances.(c) Copper cannot displace zinc from its salt solution.(d) Sodium and potassium are stored in kerosene.

7. Can you store lemon pickle in an aluminium utensil? Explain.

8. In the following Table some substances are given in Column I. In Column IIsome uses are given. Match the items in column I with those in Column II.

Column I Column II

(i) Gold (a) Thermometers

(ii) Iron (b) Electric wire

(iii) Aluminium (c) Wrapping food

(iv) Carbon (d) Jewellery

(v) Copper (e) Machinary

(vi) Mercury (f) Fuel


E X

E R

C I

S E

S9. What happens when

(a) Dilute sulphuric acid is poured on a copper plate?(b) Iron nails are placed in copper sulphate solution?

Write word equations of the reactions involved.

10. Saloni took a piece of burning charcoal and collected the gas evolved in atest tube.

(a) How will she find the nature of the gas ?(b) Write down word equations of all the reactions taking place in this

process.

11. One day Reeta went to a jeweller’s shop with her mother. Her mother gaveold gold jewellery to the goldsmith to polish. Next day when they broughtthe jewellery back, they found that there was a slight loss in its weight.Can you suggest a reason for the loss in weight?

Extended Learning — Activities and Projects

1. Prepare Index Cards for any four metals and four non-metals. Thecard should have information like name of metal/non-metal; itsphysical properties, chemical properties and its uses.

2. Visit a blacksmith and observe how metals are moulded.

3. Suggest an experiment to compare the conductivity of electricity byiron, copper, aluminium and zinc. Perform the experiment andprepare a short report on the results.

4. Find out the locations of the deposits of iron, aluminium and zincin India. Mark these in an outline map of India. In which form arethe deposits found? Discuss in the class.

5. Discuss with your parents/neighbours/goldsmiths why gold ispreferred for making jewellery.

6. Visit the following websites and enjoy the quiz on metals and non-metals:

� chemistry.about.com/library/weekly/bl050303a.htm� chemistry.about.com/od/testsquizzes/Chemistry_Tests_

Quizzes.htm� www.syvum.com/cgi/online/mult.cgi/squizzes/science/

metals.tdf?0� www.gcsescience.com/q/qusemet.html� www.corrosionsource.com/handbook/periodic/metals.htm

8 materials - metals and non-metals

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