13 METALS AND NON-METALS

13 METALS AND NON-METALS

1. Elements are classified into two kinds – metals and non-metals.

2. Physical properties of metals : (1) Metals have a lustre.

(2) They are malleable and ductile. (3) Metals are good

conductors of heat and electricity. (4) At normal temperature,

metals are generally solids. (5) Metals usually have high

density.

3. Physical properties of non-metals : (1) Non-metals lack

lustre. (2) Non-metals are not malleable and ductile. (3) They

are poor conductors of heat and electricity. (4) At normal

temperature, non-metals are in the solid or gaseous states.

(Bromine is in liquid state.) (5) Non-metals have low density.

4. Chemical properties of metals : (1) Metals combine with

oxygen in the air to form their metal oxides. When magnesium

burns in air, it combines with oxygen to form magnesium oxide.

2Mg_O

_

IIIIIIIJ 2MgO

(2) The oxides of metals are alkaline in nature.

5. The action of acids on metals : Place a magnesium ribbon, a

thin sheet of aluminium, iron filings and copper wire in four

different test tubes. Now using dropper add dil. HCl to each of the

test tubes, observe the reactions carefully. If reaction does not

take place, heat the test tube slightly and take a burning

matchstick near the mouth of each of the test tubes. Metals

reacts with dil. HCl and produce hydrogen gas that burns with a

pop sound when a burning matchstick is brought near the mouth

of the test tube. This shows hydrogen gas is combustible.

6. The action of bases on metals : When bases react with metals,

hydrogen gas is formed.

7. Uses of metals : (1) Metals are widely used in making cooking

utensils. (2) Copper is used in making wires and in electrical

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gadgets, radios, refrigerators, etc. (3) Iron and aluminium

sheets are used to make roofs of houses. (4) Gold and silver are

used in making coins and ornaments. (5) Tin is specially used

for coating articles made from steel. (6) Mercury is used in

thermometers. 

8. Uses of non-metals : (1) Graphite is used in pencils and one of

the electrodes in an electrochemical cell. (2) Silicon is used in

the solar cell. (3) Silicon dioxide is used in making glass and

cement. (4) Red phosphorus is used in making safety matches,

crackers, germicides and explosives. (5) Sulphur is used in

the production of acids and also in some medicines and gun

powder.

9. Noble metals : Some metals are found in nature in the form of

elements. They are not affected by air, water, acids and heat,

etc. Hence, they are called noble metals. They do not generally

take part in chemical reactions. Gold and platinum are noble

metals. They are used for making ornaments. Gold was also

used to make coins in olden days. Platinum is used in some

medical instruments. Some silver articles are coated with gold.

10. Purity of gold : The purity of gold is measured in carats.

24-carat is considered as gold of 100% purity. 24-carat gold is

pure and very soft. 100% pure gold bends or breaks easily.

Therefore, copper or silver is added to gold in the necessary

proportion while making ornaments.

11. Corrosion : Metals when kept exposed to moist air, some gases

present in air react with metals to form metal compounds on

the surface. This action that wears the metals is known as

corrosion. A layer of grease or oil is applied on the surface of

metals to prevent corrosion. Iron is galvanised, ships are coated

with enamel paints.

12. Alloy : A homogeneous mixture of two or more metals or of

is called an alloy. Copper and tin are

used to make an alloy called bronze. When iron and carbon are

mixed, an alloy steel is formed. The alloy, stainless steel is

made from iron, carbon and chromium.

Questions and Answers

Q. 1 Answer the following questions :

(1) Which of the following substances are hard and have

shiny surfaces ?

Aluminium, sulphur, carbon, copper, silver, soil, chalk and

magnesium.

Ans. Aluminium, silver, copper and magnesium are hard and

shiny, while carbon, sulphur, soil and chalk are not hard and shiny.

(2) What is meant by malleability ?

Ans. The property of metal by which they can be beaten into

thin sheets is called malleability.

(3) What is meant by ductility ?

Ans. The property of metal by which it can be drawn into

wires is called ductility.

* (4) Why does a copper vessel shine again after scrubbing ?

Ans. If a copper vessel is not used for long time, then coating of

black copper oxide is formed on the vessel. When the vessel is

scrubbed with tamarind, tartaric acid in tamarind helps to remove

black copper oxide. Copper being a metal, it shines. As a result a

copper vessel shines again after scrubbing.

* (5) Whyis copper used for electrical wiring in our houses ?

Ans. Copper is a good conductor of electricity. It possesses the

property of ductility. Hence, copper is used for electrical wiring in

our houses.

* (6) Why is it possible to draw silver into a wire when even

a long pencil-point breaks so easily ?

Ans. Silver is a metal and possesses the property of ductility

and hence it can be drawn into wire. Pencil-lead is made from

graphite, a non-metal and hence is not ductile. Therefore, even a

long pencil-point breaks so easily.

Answers to the Questions given on page 126 of the textbook

 What is the size of the sheet you can get from

1g gold ?

Ans. A sheet of area 2 m_ obtained from 1g gold, is the

record.

 Why is copper or silver used in coins ?

Ans. Silver and copper are malleable. They can be beaten

into thin sheets and can be given the desired shape. Hence,

copper or silver is used in coins.

 Is diamond, which shines, a metal ?

Ans. No. A diamond is a form of carbon, a non-metal.

Hence, even though it shines, it is not a metal.

 Give the properties of metals.

Ans. (1) Metals have a lustre. (2) Metals are malleable. They

can be beaten into thin sheets. (3) Metals are ductile. They can be

drawn into wires. (4) They are good conductors of heat and

electricity. (5) At ordinary temperature, metals are generally solid.

(Exception : Mercury is liquid.) (6) Metals usually have high density.

Give the properties of non-metals.

Ans. (1) Non-metals lack lustre. (2) As non-metals are brittle,

they are not malleable. (3) They are not ductile. (4) Non-metals

are poor conductors of heat and electricity. (5) At ordinary

temperature, non-metals are in the solid or gaseous state.

(Exception : Bromine is liquid.) (6) Non-metals have low density in

the solid state.

 Classify the following elements into metals and nonmetals

:

Silicon, gold, silver, sulphur, carbon, aluminium, copper and

phosphorus.

Ans. Metals : Gold, silver, aluminium and copper.

Non-metals : Silicon, sulphur, carbon and phosphorus.

 How will you show that metal oxides are alkaline ?

Ans. Take magnesium oxide in a test tube. Add water in the

test-tube. Shake the test-tube. Test the solution with red or blue

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litmus paper. Blue litmus paper remains as it is while red litmus

paper turns blue. This shows that metal oxides are alkaline in

nature.

Answer to the Question given on page 128 of the textbook

* How do we clean silver or brass articles that have got

tarnished ?

Ans. Silver or brass articles are cleaned with tamarind.

Tartaric acid in tamarind helps to remove the stains.

(12) Give the uses of metals.

Ans. (1) Metals are widely used in making cooking utensils.

(2) A metal like copper is used in making wires and in electrical

gadgets, radios, refrigerators, etc. (3) Iron and aluminium sheets

are used to make roofs of houses. (4) Gold and silver are used in

making coins and ornaments. (5) Tin is specially used for coating

articles made from steel. (6) Mercury is used in thermometers.

(7) Compounds of sodium such as common salt (Sodium chloride),

washing soda (Sodium carbonate), baking soda (Sodium

bicarbonate) are useful for many purposes in everyday life.

 Give the uses of non-metals.

Ans. (1) Graphite is used as the core in pencils and also used

as one of the electrodes in an electrochemical cell. (2) Silicon is

used in the solar cell. (3) Silicon dioxide is used in making glass and

cement. (4) Red phosphorus is used in making safety matches,

crackers, germicides, explosives, etc. (5) Sulphur is used in the

production of acids, also in some medicines, gunpowder, etc.

 What is meant by noble metals? Give two examples.

Ans. Some metals are found in nature in the form of elements,

which are not affected by air, water, acids, heat, etc. Hence, they are

called noble metals. Examples : Gold, platinum.

 Give the uses of noble metals.

Ans. (1) Gold and platinum are mainly used for making

ornaments. (2) Gold was also used to make coins in olden days.

(3) Platinum is used in some medical instruments. (4) Some silver

articles are coated with gold.

 What is meant by corrosion ? Give two examples.

Ans. Metals, when kept exposed to moist air, the gases in air

react with metals to form metal compounds on the surface. This

action that wears the metals is known as corrosion.

Examples : Oxygen reacts with iron, iron articles get covered

with reddish substance. Carbon dioxide reacts with copper develop

yellowish green patches and hydrogen sulphide reacts with silver,

articles turn black.

 How is corrosion prevented?

Ans. (1) A layer of grease or oil is applied on the surface of

metals to prevent corrosion. (2) Iron is galvanised to prevent

rusting. (3) Ships are coated with enamel paints. The enamel paints

contain metals like zinc or magnesium which prevent the corrosion

of the metal sheets by the salty sea water.

 What is meant by an alloy ?

Ans. A homogeneous mixture of two or more metals or of

is called an alloy.

 Give two characteristics of alloys.

Ans. (1) Alloys contain metals in specific proportions. (2) The

physical properties of an alloy are different from those of its

constituents, but chemical properties remain the same.

Q. 3 Write short notes on the following :

(1) The noble metals (2) The purity of gold (3) Corrosion

(4) Alloys.

Ans. (1) The noble metals : For answer see Q. 1 (14), (15).

(2) The purity of gold : (1) The purity of gold is measured in

carats. (2) Twenty-four carat gold is considered as gold of 100%

purity. (3) 24-carat pure gold is very soft. 100% pure gold bends or

breaks easily. Therefore, copper or silver is added to gold in the

necessary proportion (while making ornaments). (4) Generally,

22-carat gold is used in making ornaments.

Percentage of Gold Carat

100% 24

91.8% 22

75% 18

58.5% 14

50% 12

42% 10

(3) Corrosion : See the answers to Q. 1 (16) and (17).

(4) Alloys : (1) A homogeneous mixture of two or more metals

or of is called an alloy. (2) They contain

metals in specific proportions. (3) The physical properties of an

alloy are different from those of its constituents, but chemical

properties remain the same. (4) Copper and tin are used to make an

alloy called bronze. It is hard and corrosion resistant. (5) When

iron and carbon are mixed, an alloy steel is formed. It is a stronger

material. (6) The alloy, stainless steel is made from iron, carbon

and chromium. It is more durable, clean and does not rust.

Q. 4 Distinguish between : Metals and Non-metals.

Ans. Metals Non-metals

1. Metals have lustre. 1. Non-metals do not have

lustre.

2. Metals are malleable. 2. Non-metals are not malleable.

3. Metals are ductile. 3. Non-metals are not ductile.

4. Metals are good conductors

of heat and electricity.

4. Non-metals are poor conductors

of heat and electricity.

5. At room temperature, metals

are in the solid state.

(Exception : Mercury is

liquid.)

5. At room temperature, nonmetals

are in the solid, or

gaseous state. (Exception :

Bromine. It is in liquid state.)

6. Generally, metals have high

densities.

6. Generally, non-metals have

lower densities.

* Q. 5 Give scientific reasons :

(1) Gold and silver are used in coins.

Ans. (1) Gold and silver are malleable. (2) They can be beaten

into thin sheets and can be given desired shape. Hence, gold and

silver are used in coins.

(2) Ornaments are generally not made from 24-carat gold.

Ans. (1) 24-carat gold is considered as gold of 100% purity.

(2) 24-carat pure gold is very soft. 100% pure gold breaks or gets

bent easily. Therefore, ornaments are generally not made from

24-carat gold.

(3) Ships are painted at frequent intervals.

Ans. (1) The metal sheets of ships are made from iron. (2) Due

to salty sea water, the metal sheets of ships get rusted and corroded.

Paints contain metals like zinc or magnesium. This prevents the

metal surface of the ship coming into direct contact with salty sea

water. Therefore, ships are painted at frequent intervals.

(4) Gold and platinum are called noble elements.

Ans. (1) The metals such as gold and platinum are found in

nature in the form of elements. (2) They are not affected by water,

air, acids, heat and also do not take part in chemical reactions.

Hence, they are called noble metals.

(5) Stainless steel has more lustre than iron.

Ans. (1) Stainless steel is an alloy made from iron, carbon and

chromium. Iron is a metal. (2) In an alloy, the physical properties of

the constituent elements do not remain the same. Hence, stainless

steel has more lustre than iron.

Q. 6 Answer the following questions in one sentence

each :

(1) Give the classification of elements.

Ans. Elements are classified into metals, non-metals and

metalloids.

(2) Name two metals which are malleable.

Ans. Iron and aluminium are malleable metals.

(3) Name two metals which are ductile.

Ans. Gold and platinum are ductile metals.

(4) Name two metals which are good conductors of heat.

Ans. Iron and copper are good conductors of heat.

(5) Name a metal which is in liquid state at ordinary

temperature.

Ans. Mercury is in liquid state at ordinary temperature.

(6) What happens when red and blue litmus papers are

inserted in a solution of metal oxide.

Ans. When red and blue litmus papers are inserted in a

solution of metal oxide, red litmus paper turns blue.

(7) Name two compounds of sodium.

Ans. Compounds of sodium : sodium chloride and sodium

carbonate.

(8) Which non-metal is used in pencils ?

Ans. Graphite is used as the core in pencils.

(9) Name the term used to express the purity of gold.

Ans. The purity of gold is expressed in carat.

(10) Name a non-metal which is in liquid state at ordinary

temperature.

Ans. Bromine is in liquid state at ordinary temperature.

Q. 7 Find the odd one out and give the reason :

(1) Magnesium, Mercury, Sodium, Iron.

(2) Magnesium, Aluminium, Sulphur, Copper.

(3) Iron, Copper, Graphite, Phosphorus.

(4) Tin, Bronze, Steel, Stainless steel.

Ans. (1) Mercury. Other metals are in solid state at normal

temperature. (2) Sulphur. Others are metals. (3) Phosphorus.

Others are good conductors of electricity. (4) Tin. Others are

alloys.

Q. 8 Taking into consideration the relationship in the

first pair, complete the second pair :

(1) Mercury : Metal : : Carbon : ……… .

(2) Wood : Bad conductor of electricity : : Copper : ……… .

(3) Gold : Noble metal : : Copper : ……… .

(4) Iron and carbon : Steel : : Copper and Tin : ……… .

Ans. (1) Non-metal (2) Good conductor of electricity (3) Metal

(4) Bronze.

Q. 9 State whether the following statements are True or

False. If a statment is false, correct it and rewrite :

(1) Sulphur is a shiny substance.

(2) Platinum, gold are well-known as highly ductile metals.

(3) The oxides of metals are acidic in nature.

(4) Carbon dioxide is used in making glass and cement.

(5) Gold and silver are used to make coins and ornaments.

(6) Mercury is used in thermometers.

(7) Gold is used in some medical instruments.

(8) 24-carat gold is used for making ornaments.

(9) The chemical properties of an alloy are different from its

constituents.

Ans. (1) False. Sulphur is not a shiny substances. (2) True.

(3) False. The oxides of metals are alkaline in nature. (4) False.

Silicon dioxide is used in making glass and cement. (5) True.

(6) True. (7) False. Platinum is used in some medical instruments.

(8) False. 22-carat gold is generally used for making ornaments.

(9) False. The chemical properties of an alloy are same as its

constituents.

Q. 10 Fill in the blanks :

*1. (1) Gold of 100% purity is ……… carat gold.

(2) Bronze contains the metals ……… and ……… .

(3) The ……… gas is released when metals react chemically

with acids.

(4) Oxides of metals have ……… properties.

(5) The non-metal ……… is used in gunpowder.

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Ans. (1) 24 (2) copper and tin (3) hydrogen (4) alkaline

(5) sulphur.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

2. (1) Metals are ……… conductors of heat and electricity.

(2) When bases react with metals, ……… gas is released.

(3) ……… is used in thermometers.

(4) ………litmus turns………in a solution of magnesium oxide.

Ans. (1) good (2) hydrogen (3) Mercury (4) Red, blue.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

3. (1) The salt sodium chloride is a ……… .

(2) ……… is used as one of the electrodes in an electrochemical

cell.

(3) ………, a metal, is in liquid state at normal temperature.

(4) ……… is used in the solar cell.

Ans. (1) compound (2) Graphite (3) Mercury (4) Silicon.

Q. 11 Choose the correct alternative and complete the

following statements :

(1) ……… wires are used in electrical gadgets.

(a) silver (b) tin (c) copper (d) silicon

(2) 22-carat gold is gold of ……… purity.

(a) 100% (b) 91.8% (c) 75% (d) 44%

(3) The alloy steel is made from ……… .

(a) iron and carbon (b) copper and carbon

(c) iron and tin (d) tin and carbon

(4) ……… is used in making germicides and explosives.

(a) Sulphur (b) Red phosphorus

(c) Graphite (d) Silicon

(5) The chemical name of baking soda is ……… .

(a) sodium carbonate

(b) sodium chloride

(c) sodium

(d) sodium bicarbonate

(6) The alloy ……… is made from iron, carbon and chromium.

(a) bronze (b) steel (c) stainless steel (d) chrome steel

(7) ……… metal is in liquid state.

(a) Mercury (b) Sodium (c) Magnesium (d) Silver

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(8) When copper reacts with hot concentrated sulphuric acid,

……… gas is formed.

(a) hydrogen (b) oxygen

(c) sulphur dioxide (d) carbon dioxide

(9) Silver gets corroded due to ……… gas.

(a) oxygen (b) hydrogen sulphide

(c) carbon dioxide (d) hydrogen

(10) The non-metal ……… is in liquid state at normal

temperature.

(a) Hydrogen (b) Chlorine (c) Nitrogen (d) Carbon

Ans. (1) Copper (2) 91.8% (3) iron and carbon (4) Red

phosphorus (5) sodium bicarbonate (6) stainless steel (7) Mercury

(8) sulphur dioxide (9) hydrogen sulphide (10) bromine.

Q. 12 Match the following :

* [1] ‘A’ ‘B’

(1) Mercury

(2) Graphite

(3) Sulphur

(4) Steel

(5) Stainless steel

(a) Alloy of iron, nickel, chromium

(b) Alloy of iron and carbon

(c) The ‘lead’ in a pencil

(d) Medicines

(e) Thermometer

Ans. (1) Mercury– Thermometer. (2) Graphite – The ‘lead’ in a

pencil. (3) Sulphur – Medicines. (4) Steel – Alloy of iron and carbon.

(5) Stainless steel – Alloy of iron, nickel, chromium.

[2] ‘A’ ‘B’

(1) Mercury

(2) Carbon

(3) Noble metal

(4) Bronze

(5) Metal oxide

(a) Gold

(b) Alkaline nature

(c) Metal

(d) Non-metal

(e) Alloy of copper and tin

Ans. (1) Mercury– Metal. (2) Carbon – Non-metal. (3) Noble

metal – Gold. (4) Bronze – Alloy of copper and tin. (5) Metal

oxide – Alkaline nature.