Modern Graded Science - 9

Chapter

12 M e t a l s

Total estimated PDS: 4/ (3T/1P

Competencies
On completion of this chapter, the students will be competent to:

explain the properties of metals.
write the differences between metals and non-metals.
write the importance of sodium, zinc and potassium in the living organisms.
mention the harmful effects of mercury and lead.

There are many objects in our surroundings. These objects are made up of various materials
such as plastic, wood, glass, iron, copper, etc. On the basis of certain basic properties, all the
elements have been divided into metals, metalloids and non-metals. Metals are those elements
which can conduct heat and electricity. Objects like utensils, vehicles, aeroplanes, trains,
electrical appliances, etc. are usually made up of metals. In the absence of these objects, our
life would be very difficult. Do you know our blood contains iron and chlorophyll of plants
contains magnesium? Without iron and magnesium metals, we cannot imagine a single living
plant and animal remaining alive on our planet.

Similarly, metals like calcium, potassium, sodium, copper and zinc are also essential metals
for the healthy growth as well as regulation of various activities of the human body. For
example, zinc is one of the most important components of about 300 enzymes like carbonic
anhydrase. The enzymes regulate many body activities. What would happen if zinc is deficit
in human body? The deficiency of zinc causes retardation of senses of smell and taste, reduces
the immunity power, results in hair loss and slow growth rate among the children. These
deficiency symptoms make life difficult.

General properties of metals and non-metals

The general properties of metals and their detailed
comparison with non-metals can be studied with
the help of various activities as described below.

1. State Fig. 12.1 physical properties of metals

Most metals are solid at room temperature. There Metals 197
are five metals which are liquid at or close to room
temperature. Cesium, francium, gallium, rubidium

and mercury are the liquid metals. Most metals are solid at room temperature because this
temperature is not enough to provide them required kinetic energy to overcome the forces of
attraction or convert them to liquid or gas state.

Non-metals are found in all three states at odinary temperature. Bromine is only one non-
metal that exists in liquid state. Three elements such as hydrogen, nitrogen and oxygen are in
gases state and four elements such as carbon, phosphorus, selenium and sulphur are found in
solid state at ordinary temperature.

2. Brittleness and Hardness

Activity 12.1
To find the brittleness of materials

Collect iron nails, pieces of copper, plastic sheets, utensils of aluminium, pencil lead (carbon),
sulphur, apples and jelly. Take each of them in your hand one by one and feel them with your
eyes closed. Can you distinguish them just by touching? Yes, but how could you do that? By
feeling them, you will say jelly is soft and iron metal is hard. Try hammering each of them as
well. Which one of them can be broken easily or not? Make a list of them in your notebook
using the table given below.

Generally, metals are hard but nonmetals are soft and brittle because their molecules are
closely packed except in lithium,
sodium and potassium. These Objects Hard and less brittle Soft and brittle
metals are soft and brittle i.e. Sulphur
they can be broken easily. Iron nail, piece of cop- Iron nail ..................................
Non-metals like sulphur are per, plastic sheet, ........................................ ..................................
aluminium utensil, ........................................ ..................................
sulphur, pencil lead ........................................ ..................................
(carbon) ........................................

generally soft except diamond (a
form of carbon).

3. Metallic lustre

Activity 12.2
To show metals possess metallic lustre

Draw a line one after Objects has metallic lustre does not have metallic lustre
another on the objects Iron nail, plastic sheet, Iron nail Plastic Sheet
taken for the Activity aluminium utensil, .............................................. ..............................................
12.1 above using a sulphur, pencil lead, .............................................. ..............................................
small stone. Which piece of copper .............................................. ..............................................
one of these can be .............................................. ..............................................

possessed shining or metallic lustre. Observe each of them and make a list in your notebook

198 Modern Graded Science Class 9

as in the table given below. Generally, metals possess metallic lustre when they are freshly cut
or when a line is drawn on it except lithium. The shining property of metals is called metallic
lustre. Non-metals, except graphite (carbon) and iodine do not possess any metallic lustre.

4. Malleability

Activity 12.3
To show that metals are malleable

Take all the objects Objects Malleable Non-malleable
used in activity Iron nail Piece of copper Sulphur
12.1 and hammer Piece of copper ............................................. .............................................
each of them one Plastic sheet ............................................. .............................................
by one using a Sulphur ............................................. .............................................
hammer. What Aluminium utensil ............................................. .............................................
kind of change can Pencil lead ............................................. .............................................

be seen on each object? Observe and list in your notebook as in the given table. Metals can be
beaten into a thin plate. So metals are malleable. This phenomenon is called malleability. Due
to this property, metals are used to make different utensils, tools and arms.Non-metals like
sulphur cannot be beaten to a thin plate. Thus non-metals are non- malleable.

5. Ductility

Activity 12.4
To show that metal have the property of ductility

Take different objects used for Activity 12.3. What are the different malleable metals from
which wire can be made? Have you ever seen? Discuss in the classroom and write in your
notebook as in the given
Objects Ductile Non-ductile

table. The property of a Iron nail, piece of Aluminium Sulphur
metal which helps it to copper, plastic sheet, ............................................. .............................................
make into wire is called aluminium utensil, ............................................. .............................................
ductility and the metal sulphur, pencil lead ............................................. .............................................
is called ductile. Metals (carbon) ............................................. .............................................
............................................. .............................................

like iron, copper, aluminium, etc. are ductile. Non-metals are non-ductile as they cannot be
drawn into wires.

6. Conductivity

Activity 12.5 Sodium and potassium are highly
To demonstrate that metals are good conductor reactive metals so they are stored
in kerosene as they can easily

Collect different materials like a metals spoon, a safety pin, catch fire even when they come in
aluminium foil, paper, cork screw, metal scale, pencil lead, contact with air.

Metals 199

copper piece, eraser, plastic, protractor and piece of wood.

Make a simple circuit consisting of a small electric scouurrrceenotf spoon
bulb, a wire and a dry cell as shown in the figure. torch
lamp
Then the materials to be tested are connected in
the circuit at A and B one by one. Observe whether
the bulb glows or not. Enlist the materials from
which electricity is conducted.

If the bulb glows when a material is connected in Fig. 12.2 simple circuit
a circuit between A and B, the material is a metal,

otherwise, it is a non-metal. Metals are generally good conductors of electricity because they

allow an electric Objects Conducts electricity Does not conduct elec-
current through tricity

them. This property safety pin, metal spoon, safety pin paper
aluminium foil, paper, cork, ........................................... .............................................
of metals is called pencil lead, copper piece, ........................................... .............................................
eraser, plastic, protractor, ........................................... .............................................
conductivity. All the piece of wood ........................................... .............................................
........................................... .............................................
metals are good ........................................... ...........................................

conductors of

electricity. Though

silver is the best conductor of electricity in comparison to mercury. Non-metals are bad

conductors of electricity except graphite. Thus, those materials that conduct electricity are

called metals while those materials which cannot conduct electricity are non-metals.

Activity 12.6

To demonstrate that metals are good conductor

Take all the objects used for activity 12.5. Put a burning candle on the table. Then hold the
object with the help of forceps and heat it on the burning candle one by one. Touch the other
end of that heated object under the guidance of the teacher and fill the chart. Metals are
generally good conductors of heat. Non-metals like wood do not conduct heat so they are
called insulators of heat.

Objects Conducts heat Does not conduct heat
piece of wood
safety pin, metal spoon, safety pin .............................................
aluminium foil, paper, cork, ............................................. .............................................
pencil lead, copper piece, ............................................. .............................................
eraser, plastic, protractor, ............................................. .............................................
piece of wood .............................................

200 Modern Graded Science Class 9

7. Metallic clink or sonorous sound

Activity 12.7
To distinguish metal produces sonorous sound

Take a metallic vessel, a wooden vessel and a rod. Graphene was made first in the
Hit the vessels with the rod one by one. Listen to the laboratory (2003 AD). It is used as
sound produced while hitting and compare it with the a semiconductor. Now, it is highly
toll of the bell at your school. It has a sonorous sound used through the world. It is light
or metallic clink produced by the metalic vessen and and transparent but hundredth times
the bell. Metals produce a metallic clink or sonorous stronger than the steel.
sound when we strike them with a rod but non-metals
produce a dull sound.

8. Melting and boiling points

Most of the metals are generally hard because Metals Melting point Boiling point
their atoms are closely packed due to the greater
force of attraction between them. This force makes Iron (Fe) 1535°C 2850°C
them strong enough except lithium (Li), sodium Copper (Cu) 1085°C 2927°C
(Na), potassium (K), and mercury (Hg); have high Aluminium (Al) 660°C 2500°C
melting and boiling points. But non-metals have Magnesium (Mg) 650°C 1090°C
Sodium (Na) 97.79°C 882.94°C
Potassium (K) 64°C 759°C

usually low melting and boiling points. Some metals and their melting points and boiling
points have been mentioned in the table.

9. Alloy

An alloy is a homogeneous mixture of two or more metals and non-metals to obtain desirable
qualities such as hardness, lightness and
strength. Usually, alloy is a solid mass, made
by mixing two or more metals and non-
metals in molten state and then allowed to Ionic compounds have strong force of attraction
cool. The physical properties of alloys are between the ions. Therefore, it requires a lot
of energy to overcome their forces. Thus, ionic
more different from those of the constituent compounds have a high melting point.
pure metals. Brass is an alloy of zinc (10–
35%) and copper (65-90%). Bronze is also an alloy of copper (78-95%), tin (5-22%) and little
manganese, phosphorus and aluminium. Similarly, stainless steel is also and alloy of 89.4%
iron, 10% chromium, 0.35% mangnese and 0.25% carbon. An alloy which is formed by mixing
a metal and mercury is called amalgam. For example, an alloy of sodium and mercury is called
sodium amalgam.

Generally, alloys are harder, stronger and more brittle than their components but their melting
point is lower than their components. They are good conductors which have the properties
like malleablity and ductility. Only nonmetals cannot form alloys.

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Electron sea model of metals

The electron sea model states that "the metal atoms in a solid crystal lose their valence
electrons, called free electrons, which can move easily from one atom to the next atom
instead of being confined by any specific atom, due to this metal ions are immersed in a sea
of mobile electrons".

The force of attraction that occurs between the free or mobile electrons and positive metallic
ions without any chemical reaction for holding the metal atoms together is called a metallic
bond.

The presence of free mobile electrons explains most of the properties of metals. The following
properties discussed below according to the electron sea model.

1. Why do metals shine?

According to the electron sea model, when light falls on the surface of a metal the free electrons
absorb light and vibrate. Due to the vibration, the vibrating electrons emit the energy in the
form of light. Hence, the surface of metals shines or becomes lustrous.

2. Metals are malleable and ductile. Why?

According to the electron sea model, the
bonds between metal ions and mobile free
electrons are non-directional. Due to this the
attraction between positive metal ions and
free electrons is uniform in all directions.
Hence, when external force (stress) is applied
on metals, the positive metallic ions slide
from one side to another. Thus, the metal is Fig. 12.3 malleability and ductility

deformed to a sheet or a wire without destroying the structure of the metal crystal. This ability
makes a metal malleable and ductile.

3. How can metals conduct heat and electricity?

When one end of a metal is heated, the free electrons present in that region absorb heat and
acquire large kinetic energy. Hence, according to the electron sea model, the valance or free
electrons of metals become mobile and move from the heated end to the another end. Thus,
the heat gets conducted.

According to the electron sea model, valence electrons are not bound to any particular metallic
nucleus but they are highly mobile as free electrons in metals. When an electric current is
applied into an end of the metallic conductor, the free electrons start moving from that end to
another end. In this way, electricity is conducted through metals.

202 Modern Graded Science Class 9

Chemical properties of metals

1. Reaction with oxygen

Activity 12.8
To prove magnesium burns in oxygen to from magnesium oxide

Take a magnesium ribbon and burn it in bunsen burner or spirit lamp placed above the paper

with the help of a tong. It burns brightly and changes into whitish ash of magnesium oxide.

2Mg + O2 ∆ 2 MgO (Magnesium oxide)

Thus, metals form metallic oxides by burning in oxygen. Some other examples are:

2Al + 3O2 ∆ Al2O3 (Aluminium oxide)

-2Ca + O2 ∆ 2 CaO (Calcium oxide)

2. Reaction with acids

Activity 12.9
To produce metallic salts by treating metal and dilute hydrochloric acid

Take a small piece of magnesium in a test tube. Add 2 ml dilute hydrochloric acid in it. Observe
the reactions taking place in the test tube. Now, the metal reacts with dilute hydrochloric acid
and forms salt and hydrogen gas.

Mg + dil 2HCl → Mg Cl2 + H2↑ When an iron rod is placed in an open
Thus, metals react with acid to give salt and place for few days, the surface of the iron
hydrogen. Some other examples are: rod appears reddish brown in colour. This
2Al + dil 6HCl → 2Al Cl3 + 3H2↑ is due to the formation of rust. Rust is a
reddish brown compound of iron, called iron
2Fe + dil 6HCl → 2Fe Cl3 + 3H2↑ oxide. This iron oxide is formed when iron
and oxygen react in the presence of water or
3. Reaction with hydrogen moisture in the air.

Metals react with hydrogen and they form unstable
metallic hydrides. For example,
Mg+H2 → MgH2 (magnesium hydride)
Ca+H2 → CaH2 (calcium hydride)

4. Displacement reaction

Activity 12.10
To show more reactive metal (iron) replace the cupper from the copper sulphate

Take 20 ml copper sulphate solution in a beaker and 20 ml ferrous sulphate solution in another.
Dip an iron nail into the solution of copper sulphate and a copper plate into the solution of
ferrous sulphate with the help of thread. After sometime, take out both of them, the iron nail
and the piece of copper, from the solutions. Observe each of the metals. Why does the iron

Metals 203

nail seems like the copper plate? Why does this happen? It is because highly reactive metals
replace the less reactive metals from their respective salt solutions. For example,
Fe + Cu SO4 → Fe SO4 + Cu
Cu + Fe SO4 → No reaction
But there is no reaction between Cu and FeSO4 as Cu is less reactive than FeSO4. Therefore, Cu
cannot displace Fe from FeSO4 soluction.

Difference between metals and non-metals

Metals can be distinguished from non-metals due to their typical characteristics. Their
differences are given in the table below.

S. No. Properties Metals Non-metals

1. State Metals, except mercury, are solid at Non-metals are found in all three states
the ordinary temperature at room temperature.

2. Metallic lustre They possess metallic lustre when Non-metals, except iodine and graph-
they are freshly cut, except lithium. ite, do not possess any metallic lustre.

3. Hardness They are generally hard except Na They are generally soft except dia-
and K. mond.

4. Breakability They are hardly broken into pieces. They can be easily broken.

5. Melting and boiling The boiling and the melting points They have usually low melting and

point of metals are generally high. boiling points.

6. Metallic clink sound Metals can produce a sonorous They produce a dull sound.
sound.
They are non-malleable.
7. Malleability They are malleable. They are non-ductile.

8. Ductility Metals are ductile.

9. Conductivity They are generally good conductors They, except graphite, are generally
10. Specific gravity of heat and electricity. poor conductors of heat and electricity.

They, except Li, Na, K, Ca, etc. have They, except diamond, have low specif-
high specific gravity. ic gravity.

11. Electrochemi-cal They are electropositive in nature. They are electronegative in nature.
behaviour
Metals have the dissolving power to They generally do not form alloy.
12. Alloy formation other metals to form homogeneous
mixture, the alloy. They form acidic oxides. Except CO,
13. Reaction with NO2, H2O, (neutral oxides).
oxygen Metals form basic oxides except They usually combine with hydrogen to
Cr2O3, ZnO, MgO. give stable hydrides.
14. Reaction with
hydrogen Metals rarely combine with hydro-
gen to form unstable hydrides.

15. Reaction with acids Most of the metals react with dilute Non-metals do not form salt and hydro-
acids to form salt and hydrogen gas. gen with acids.

204 Modern Graded Science Class 9

Metalloids

There are some elements like silicon (Si), arsenic (As), The relative position of ions in the
antimony (Sb), germanium (Ge) etc. which show the electrochemical activity series
properties of both metals and non-metals. Such elements
are called metalloids. They belong to the borderline Cation Anions
between metals and non-metals in the periodic table. K+ SO4– –
Metalloids possess the following characteristics: Ca++ NO3–
Na+ Cl–
1. They are poor conductors of heat and electricity Mg++ Br–
like non-metals at a low temperature but they are
good conductors like metals at a high temperature.

2. They possess a metallic lustre like metals. Al+++ I–
3. They can form alloys. Zn++ OH–
4. They are neither malleable nor ductile like non- Fe++
Sn++
metals. Pb++

Role of metals for organisms H+
Cu++

A cell has about 40 elements which combine and Hg++
recombine to form 5000 chemicals. These chemicals carry Ag++
out 3000 types of reactions in the cells with the help of pt++
enzymes. Out of 40 elements, carbon (C), hydrogen (H), Au+++

oxygen (O), nitrogen (N), sulphur (S) and phosphorus
(P) are the principal elements of the cells of organisms. This is because they make up more
than 95% of the cellular structure. Moreover, biomolecules like carbohydrates, proteins, lipids,

nucleic acids are made by these elements. These elements are biological inorganic elements.
In the 17th century, it was found that iron is present in blood. In a cell, the ratio of inorganic to
organic compounds is 1:9.

Those mineral elements which play a direct role in nutrition, growth, structure and
functioning of the cell are called essential elements. There are 16 elements in plants cells
and 25-27 elements found in all types of animals cells. The essential elements are classified
into major elements or macronutrients and minor elements or micronutrients on the basis
of the ammount of their requirement.

Those mineral elements which are required relatively in a large quantity are called major
mineral elements. C, H, O, N, P, S, Ca, Na, Cl, Mg and K are the major mineral elements.

Similarly, the mineral elements which are required by the body in trace or in a small amount
are called trace or minor elements. Fe, Cu, Mn, Mo, Zn, I, Se, F, Co, Ar and V are trace elements.

Metals 205

Importance of zinc, sodium and potassium in human body

1. Zinc

Zinc is the most common essential trace element found in the body after iron. In the human
body, there are more than 300 different enzymes which require zinc to function normally. A
normal person contains about 2-3 grams of zinc in the form of compounds or ions throughout
the body. Most of the zinc is found in brain, muscles, bones, kidneys and the liver. But higher
concentration of zinc is found in the prostrate gland, semen and retina of the eyes.

Role of zinc in human body
1. Zinc is essential for division and growth of cells as well as development of bones and

wound healing.
2. It is essential for taste, smell, vision, accelerated ageing of skin, hair growth, etc.
3. It helps to increase immune system of the body against pneumonia, diarrhoea and

common cold.
4. It helps in normal growth and development of infancy during pregnancy, childhood and

adolescence.
5. It increases the fertility of men and regulate the menstrual cycle of women.
6. It enhances the action of insulin hormone in the body.
7. It is used in the treatment of a disease such as anorexia, proriasis and neurodermitis.
The deficiency of zinc in human body causes dwarfism, night blindness, diarrhoea, impaired
wound healing, delay of sexual maturation, etc.

2. Sodium (Na) and Potassium (K)

Sodium (Na) and potassium (K) are the most important mineral elements of the human body.
These are present in the form of ions in and outside the cells. The source of sodium and
potassium are the sodium chloride and food stuffs in the diet. It is very important to have
normal quantity of sodium and potassium every day to feel well and prevent from certain
health hazards.
Biological role of sodium and potassium
1. Sodium (Na+) and potassium (K+) ions have biological importance for human being and

other organisms. The different concentrations of Na+ to K+ ions in and outside of the cell
produce an electrical potential across the membrane, which helps the functioning of the
nerve and the muscle.
2. It is believed that Na+ ions are actively expelled from the cells and K+ ions are actively
taken up by the cells. This ion transport is called sodium-potassium (Na+/K+) pump. The
sodium-potassium pump (Na+/K+ pump) helps with responding to stimuli, transmitting
nerve impulses, maintaining effective transport and regulating cellular volume.
3. Sodium helps to regulate fluids in the body. It also helps with muscle contraction.

206 Modern Graded Science Class 9

4. Sodium and potassium work together to regulate the water and acid base balance (pH) in
the blood and tissues.

5. Potassium ions (K+) inside the cell are important for metabolism of glucose, synthesis of
proteins and activation of some enzymes.

6. Potassium ions (K+) are also important in maintaining blood pressure and heart
functioning properly.

The adequate and balanced quantities of sodium and potassium ions (Na+/K+) are a must for
the living organisms including human beings. If the ratio of Na+ to K+ ions inside and outside
the cells is changed in the body, it causes marked health problems such as fall or increase in
the blood pressure, spasm, migraine, paralysis, etc.

Harmful effects of mercury (Hg)

Mercury is a heavy metal found in the liquid state occurring in several forms. All forms of
mercury have no positive role but it can produce toxic effects in the human body. The harmful
effects or poisoning effects of mercury is called hydrargyria or mercurialsm. Some harmful
effects of mercury poisoning are as follows.

1. The mercury compounds or mercury vapour or droplets of mercury are toxic and fatal
to humans as they cause serious impacts on the developing nervous system, liver, lungs,
kidneys, immune and the reproductive systems.

2. It causes high blood pressure, alters heart beat rate and increases the heart attack risk.
3. During pregnancy, mercury compounds cross the placental barriers and they can

interfere with the development of foetus, and cause attention deficit and development
delay during childhood.
4. It causes impairment of speech, impairment of hearing, walking, behavior memory,
mental retardation, learning disabilities, etc.
5. It causes a "pins and needles" sensation in the hands, feet and around the mouth.

Harmful effects of lead (Pb)

Lead is a naturally occurring element found in a small amount in the earth's crust. It is found
in all kinds of environment like air, water and soil. Lead and lead compounds have been used
in a wide variety of products like paint, ceramics, pipes, gasoline, batteries, cosmetics, etc. It
has some beneficial uses but it can be toxic to humans causing many health hazards. Some of
the harmful effects of lead are as follows.
1. Lead can affect almost every organ and system in the human body. Children of below 6

years are mostly susceptible to the effects of lead.
2. The consumption of lead in the children results in behaviour and learning problems;

lower IQ and hyper activity, slow growth, hearing problem and anemia.
3. The growing body of children absorbs more lead than the adult and it badly affects their

brain and nervous system.
Metals 207

4. Sometimes, ingestion of lead can cause seizures, coma and even death.
5. Lead deposited in the bones affects the formation of blood cells and reduces the absorption

of calcium; due to this the bone becomes weak.
6. It decreases the transportation of oxygen and calcium.
7. It causes tooth decay, headache, stomachache, kidneys disorder, increase blood pressure

and incidence of hypertension.
Mercury and lead are the harmful metals so it is wise to keep the substances made by mercury
and lead away from us.

S me Reasonable Facts

1. Children are badly affected than the adults by absorbing lead because lead affects nervous
system of growing children.

2. Non-Metals can not conduct electricity because they have no free or mobile electrons

Things To Know

1. Metals are electropositive elements, which are shiny, generally heavy and good
conductors of heat and electricity. They are malleable and ductile.

2. An alloy is defined as a homogeneous mixture of two or more metals.
3. Some elements like arsenic, antimony and germanium show the properties of both

metals and non-metals. Such elements are called metalloids.
4. The shining quality of metals is called lustre.
5. Metals can be beaten into a thin plate; such property of metals is called malleability. The

metals showing this property are called malleable metals.
6. The property of a metal being made into wires is called ductility and the metal is called

ductile.
7. Non-metals are electronegative elements which cannot conduct heat and electricity.
8. The force of attraction that occurs between the free electrons and positive metallic ions

without any chemical reaction for holding metal atoms together is called metallic bond.
This metallic bond makes the metal hard and solid.
9. Metals burn in oxygen to form metallic oxides.
2Mg + O2 →2MgO
10. Metals react with dilute acid to form salt and hydrogen gas.
Zn + dil. 2HCl → Zn Cl2 + H2↑
11. There are more than 300 different enzymes that require zinc to function normally in
human beings.
12. Zinc is present in cells, tissues, bones, protoplasm, prostate gland and even in semen.
208 Modern Graded Science Class 9

13. There is about 2-3 gm zinc present in the human body.
14. Role of zinc in human body:

• for growth and cell division
• for fertility and immune system
• for taste, smell and vision
• for skin, hair and nails
15. The sodium/potassium (Na+/K+) pump helps with responding to stimuli, transmitting
nerve impulses, maintaining effective transport and regulating cellular volume.
16. Mercury and lead are the harmful metals so it is wise to keep such substances away
from us.

Things To Do

Collect some small pieces of metals found around you. Paste them on a sheet of chart paper or
specimen box and write two uses of each of them with their name.

Test Yourself

1. Multiple Choice Questions (MCQs)

a. ……………. is liquid metal.

A. magnesium B. copper C. mercury D. zinc

b. Which one of the following is a metal?

A. C B. N C. Na D. O

c. All the materials shown the property of malleability expect.......................

A. iron B. graphite C. aluminium D. silver

d. The property of a metal by which it can be drawn into wires is called....................

A. conductivity B. malleability C. ductility D. decorating

e. The metals that produce ringing sounds are said to be..........

A. sonorous B. lustrous C. soft D. hard

f. Which metal is found in human blood?

A. Fe B. Cr C. Mg D. Co

2. Answer the following questions.

a. Give an example of metal which is the best conductor of heat and shining non-metal.

b. What is of malleability?

c. What would you observe when zinc is added to a dilute hydrochloric acid? Write the
chemical reaction that takes place.

d. Name two metals which are harmful to human beings.

Metals 209

e. What are alloys?

f. Write any two properties of metalloids.

g. What do you mean by metallic bond?

h. Enlist any five properties of metals.

i. Metals are malleable and ductile. Explain on the basis of the electron sea model.

j. Graphite and iodine are non-metals but they shine. Explain it with suitable reasons.

k. Write the chemical properties of metals with an example of each.

l. Write any three points to show the importance of each:

i. zinc ii. sodium iii. potassium

m. Write any three harmful effects of:
i. Lead ii. Mercury
n. Write in brief about micronutrients and macronutrients with examples.

3. Give reasons.
a. Ionic compounds have high melting points.
b. Metals are lustrous.
c. Metals are ductile.
d. Lead is harmful for humans.
e. Metals are good conductors of electricity.
f. Metals are used to make cooking utensils?
g. Electroplating of copper can be made on iron but not in silver.

4. Differentiate between.

a. metals and non-metals (5 points)

b. metals and metalloids (3 points)

Semen : a thick white fluid containing sperms that come out from the male genital
tract

Susceptible : very likely to be harmed or influenced

Hypertension : a common disorder in which blood pressure remains abnormally high
(Reading of 140/90 mm hg or greater)

Anorexia : a prolonged disorder of eating due to loss of appetite

Adolescence : the time period between the beginning of puberty and adulthood

Spasm : a painful and involuntary muscular contraction

Enzyme : biological catalysts

Foetus : an unborn stage of organism

Impulse : electrical signals produced by sense organs

∆∆∆

210 Modern Graded Science Class 9

Chapter

13 Carbon and Its Compounds

Total estimated Pds: 5/(4T/1P

Competencies
On completion of this chapter, the students will be competent to:

show the presence of carbon in the common substances such as wood, sugar, oil, etc.
explain the physical and chemical properties of carbon.
explain the allotropes of carbon.
explain the differences between inorganic and organic compounds.

The word 'carbon' is derived from a Latin word 'carbo' meaning soot or charcoal. Carbon
has been well known to people since ancient time in the form of charcoal and soot. Besides
these, carbon is found in nature in different forms such as coal, coke, diamond, graphite, etc.
Since last twenty years, other forms of carbon have been discovered like fullerene, graphene,
etc.Carbon is a non-metal. It is unique element which forms four covalent bonds with other
carbon as well as with other elements. Due to this reason, the estimate number of carbon
compounds known today is about three million. But, now the question is which properties of
carbon are responsible for the formation of such a large number of compounds.
In this chapter, we will study about the properties of carbon and kinds of carbon compounds.

Carbon in common materials

We know that a majority of the substances such as wood, coal, petrol, plastic, paper, cotton,
sugar, food grains, etc. are made up of carbon compounds. Carbon is also a major part of all
plants and animals including human beings. In the atmosphere, it is present as carbon dioxide
and comprises about 0.03% of the total volume of the atmosphere.

Generally, carbon is black in colour. It burns easily to produce sooty smoke along with heat
and light. If any substance from the surroundings gets burnt, it changes into black charcoal
and liberates sooty smoke. This shows that such substance contains carbon.

Activity 13.1 211
To show that ghee, oil, wood and kerosene contain carbon

Apparatus: Tong, forceps, procelain basin, tripod, wire gauze, burner.
Carbon and Its Compounds

Materials: A piece of wood, oil, ghee, and kerosene.

Procedure:
1. Take a sample of the substances in an evaporating
basin one by one. Place the basin over the burner
and heat gently in a flame very carefully.

2. Repeat the process using other samples also one by
one.

Observation: On heating, these substances burn and
change into black substances like charcoal and sooty
smoke.
Conclusion: The piece of wood, ghee, oil and kerosene on Fig. 13.1 testing process of carbon
burning change into charcoal and sooty smoke. This proves that these substances contain
carbon in the various kinds of carbon compounds.

Activity 13.2

To show that sugar contains carbon

Apparatus: Test tube, test tube holder, burner.
Material: Sugar

Procedure:
1. Take a teaspoonful sugar in a test tube.

2. Hold the test tube firmly using a test tube holder and heat
it gently as shown in the figure.

3. What will you see inside the test tube?

4. On further heating, what will happen?

Observation: The sugar melts slowly and changes into a brown
coloured substance called caramel. It produces sweet smell.
Carmel on further heating changes into a black substance
called charcoal.

Conclusion: Sugar changes into sugar charcoal and produces Fig. 13.2 heating sugar
sooty smoke on heating. This shows that sugar contains carbon.

Sources of carbon

Carbon is the fourth most abundant element in the universe. It constitutes first and second
most abundant element in the earth's crust and in the human body respectively.

Carbon is found in various from such as element, carbon compounds and in the gaseous state.
Some of them are given in the table.

212 Modern Graded Science Class 9

Carbon in the Carbon in the form of compound Carbon in the gaseous
form of element and liquid states
Inorganic compounds Organic compounds

Coal Carbonates Carbohydrates Carbon dioxide
Coke Bicarbonates Proteins Carbon monoxide
Charcoal Carbides such as Calcium Fat (oil and ghee) Hydrocarbons such as
carbide (CaC2), Silicon car- methane, ethane, etc.
Diamond bide (SiC2) urine
Graphite Minerals Vitamin Petrolium
Lamp black Rocks Medicines Glycerine, Ether
Fullerene Silk, Paper, Soap, etc. Alcohol, Benzene, etc
Graphene, etc.

Nature of Carbon

Carbon is a non-metal. It belongs to group IV A and period 2 of the periodic table. Its atomic

number is 6 and atomic weight is 12. Since its atomic number is 6, it has six electrons in its

orbits or shells. These six electrons are arranged in different shells of a carbon atom as shown

alongsde. The electronic configuration of carbon (1s2, 2s2, 2p2) shows orbit KL

that carbon has 4 valence electrons. Thus, the valency of carbon is 4. electrons 2 4
To become octet, carbon shares its 4 valence electrons and forms four

covalent bonds. One carbon is bonded with four other carbons or with other elements by 4

covalent bonds. The property of carbon in which one carbon is bounded with other carbon by

a covalent bond is unique. The unique property of carbon is responsible for the formation of a

large number of compounds. There are two properties of carbon responsible for the formation

of a long chain carbon compounds by the formation of covalent bonds as mentioned below.

1. Catenation

Carbon has unique ability to form covalent bonds with other carbon atoms, giving rise to long
chain molecules of compounds. These compounds may have carbon atoms in the form of long
or branched chains. Therefore, the catenation is a unique property of a carbon atom to link
with other carbon atoms to form a long chain or branch chains with the help of covalent
bonds. For instance,

13.3 (a) long chain of carbon (b) branch chain of carbon
Carbon and Its Compounds
213

Catenation is the main reason for the presence of a large number of organic compounds in
nature. Some good examples of catenation are polythene and polyvinyl chloride (PVC), which
have a long chain of carbon attached to one another forming a large number of compounds.
There is no limit to the number of carbon atoms which can be formed in a chain. Carbon
shows the property of catenation to maximum extent due to large -C-C- bond energy and
hence forms a large number of carbon compounds.

2. Tetravalency

Carbon has four valence electrons and its valancy is 4. This velency of carbon is responsible
for making it capable for bonding with four other carbon atoms or atoms of other elements.
Carbon also forms compounds with oxygen, nitrogen, chlorine, sulphur and many other
elements. This gives rise to many compounds with specific properties. The properties of such
compounds depend on the element rather than the presence of carbon in the molecule. The
bonds that carbon forms with other elements are very strong, thus, making these compounds
very stable.

The properties of carbon such as catenation and tetravalency can form hundreds of thousands
of carbon compounds. Hence, carbon is the only element whose compounds constitute a
saperate branch of chemistry, the organic chemistry. The organic chemistry is the branch of
chemistry that deals the study of carbon compounds of living things i.e., plants and animals.

Allotropy of carbon

Carbon exists in different
forms. These forms differ
in physical properties like
melting point, boiling
point, colour, density,
conductivity but they are
all chemically same.

They also show similar

chemical properties. These Fig. 13.4 allotropes of carbon
different forms of carbon are

called allotropes. The property of an element by virtue of which it can show many physical

forms and have similar chemical properties is called allotropy. Allotropes are the elements

which exist in different forms, having different physical properties and similar chemical

properties. Carbon exists in different allotropic forms.

214 Modern Graded Science Class 9

Physical properties of different allotropes of carbon

Physical Crystalline form Amorphous form
properties Coal, charcoal, coke
Diamond Graphite Fullerene and lampblack
1. Colour (black lead) (buckyball)C60 Black
2. State Colourless and
3. Lustre transparent Dark gray Black and opaque Amorphous
4. Hardness Crystalline Non lustrous
Lustrous Crystalline Crystalline Soft/hard
5. Density Hardest substance Lustrous
(Specific gravity) known. It's hard- Lustrous Soft Different densities
6. Conductivity ness is 10 Mohs. Soft Its hardness
3.5gm/cc is 1 to 2 Mohs Bad conductor
7. Brittle
8. Solubility 2.2gm/cc Mohs 1.66gm/cc Easily or hardly
9. Sublimation broken
Bad conductor Good conductor Good conductor Insoluble in H2O
Hardly broken Easily broken of heat but pure _
buckyball is a bad
conductor of elec-
tricity

Easily broken

Insoluble in H2O Insoluble in H2O Soluble in
At 3642° C, the sol- At 3730°C, benzene
id diamond changes its solid state
to gas changes to gas At 527°C, its solid
state changes into
gas.

Activity 13.3
After 1995, two allotropes of carbon, the buckyball and graphene were discovered. Study
the shape, utility, etc. of these forms and write a short report. Present your report in the
classroom.

Diamond

Diamond is the purest and densest from of carbon. It is the
hardest substance because of its structure. In diamond, each
carbon is bonded with four other carbon atoms with a covalent
bond and it has a tetrahedral structure. Hence, it becomes
difficult to break. Its specific gravity is 3.52 and it is transparent Fig. 13.5 molecule of diamond
to X-rays. It is a bad conductor of heat and electricity, and inert because it has no free electrons.
It burns at 800°C-900°C to produce carbon dioxide. It is insoluble in all ordinary solvents.

Carbon and Its Compounds 215

Uses

1. It is used as a precious gem in jewellery.
2. It is used for cutting glass and marble, black diamond (carbonate) and for boring or

drilling on rocks.
3. It is used to make a high quality thermometer.
4. It is used to make radiation proof windows for spacecraft.

Graphite

Graphite is also called plumbago or black lead. Graphite is a
dark grey soft crystalline substance with a metallic lustre. Its
specific gravity is 2.2. It is a good conductor of heat and electricity
because it has free electron. In graphite, each carbon is attached
to their other carbon atoms with a covalent bond and the form a
hexagonal structure. It is found in a two dimensional structure
in which hexagonal sheets lie one above the others to form stack. Fig.,13.6 molecule of graphite
They are placed one above the others with a weak Vander-waal force. It is insoluble in ordinary
solvents.

Uses

1. It is used to make pencil lead.

2. It is a good conductor of heat and electricity because of its one free electron with each
carbon atom of the graphite layers.

3. The mixture of graphite and clay is used to make electrodes.

4. When graphite is heated at 700°C, it gives carbon dioxide.

5. It is slippery and, therefore, used as lubricant.

6. It is used for coating on iron in order to prevent rusting.

Difference between diamond and graphite

Diamond Graphite

1. It is the hardest substance known. 1. It is soft and slippery.

2. It is a transparent and colourless substance 2. It is an opaque, dark grey and shiny

with bright appearance. substance.

3. It is a bad conductor of heat and electricity. 3. It is a good conductor of heat and
electricity.

4. Its specific gravity is 3.52. 4. Its specific gravity is 2.2.

216 Modern Graded Science Class 9

Chemical properties of carbon

1. Combustion: When carbon burns in excessive amount of oxygen, it yields carbon dioxide.

But, if the presence of oxygen is insufficient, it gives carbon monoxide.
∆
C + O2 ∆ CO2+ Heat and light
2C + O2 2CO + Heat and light

2. Reducing nature: Carbon is a good reducing agent. It is used for reducing less reactive

metal oxides like lead oxide and zinc oxide to their corresponding metals.

PbO + C ∆ Pb + CO

ZnO + C ∆ Zn + CO

3. Reaction with steam: When carbon is heated with steam (water vapour) at about 900 -
1000°C, a mixture of carbon monoxide and hydrogen is produced.

C + H2O 900°C - 1000°C CO + H2 (water gas)

The mixture of carbon monoxide and hydrogen gas is called water gas. Water gas is used
as the source of heat in different industries because it produces much heat on burning.

4. Reaction with metal: When carbon reacts with a metal, carbide is formed.

2C + Ca CaC2 (Calcium carbide)

5. Reaction with lime and silica: When carbon reacts with quick lime and silicon oxide

separately, they react together to give calcium carbide and silicon carbide respectively.

Silicon carbide (SiC) is a manmade hardest substance like diamond.

3C + CaO CO + CaC2 (Calcium carbide)

SiO2+3 C 2CO + SiC (Silicon carbide)

Organic and inorganic compounds

About 200 years ago, it was believed that organic compounds were produced only by natural
processes conducted in different organs of plants and animals. At that time, it was believed
that the formation of organic compounds in living organisms took place under the influence
of vital force (a mysterious force) and they could not be synthesized in a laboratory.

It was in 1828 AD that the German Chemist Friedrich Wohler prepared an organic substance
i.e. urea synthetically in the laboratory by heating an inorganic compound ammonium cyanate
and disproved the concept of vital force of life.

NH4CNO (ammonium cyanate) Heat NH2 - CO - NH2 (urea)

Thereafter, numerous organic compounds were synthesized artificially. Hence the term organic

is now used in a broad sense to describe all compounds of carbon, whether they are natural

Carbon and Its Compounds 217

or artificial. Some examples of organic compounds are methane, ethane, wax, kerosene, sugar,
alcohol, urea, esters, glycerol, benzene, fatty acids, ether, etc. The organic compounds are
studied under a seprate branch of chemistry. The branch of chemistry concerned with the
compounds of carbon is termed as organic chemistry.
The substances derived from minerals are called inorganic compounds (other than organic).
In short, we can say that inorganic compounds do not contain carbon. Some examples of
inorganic compounds are hydrochloric acid, sodium chloride, sulphuric acid, potassium
hydroxide, etc. The branch of chemistry concerned with inorganic compounds other than
carbon is called inorganic chemistry.
But certain simple carbon compounds such as carbon dioxide (CO2), carbon monoxide (CO),
carbonates and bicarbonates of metals [Na2CO3, CaCO3, Mg (HCO3)2, etc.] are traditionally
considered to be inorganic compounds.

Difference between organic and inorganic compounds

Organic compounds Inorganic compounds

1. Most of the carbon containing compounds 1. The compounds of elements except hydrocarbon are
are called organic compounds. called inorganic compounds.

2. Generally, organic compounds such as wax, 2. Generally, inorganic compounds such as copper
kerosene, ghee, oil, etc. are sulphate, sodium chloride, etc. are soluble in
insoluble in water but they are soluble in water but they are insoluble
solvents like benzene, ether, etc. inorganic solvents.

3. Generally, they have a low melting and boil- 3. They have a very high melting and boiling point.
ing point.

4. Organic compounds burn easily 4. Inorganic compounds do not burn easily.

5. They are covalent compounds. 5. Usually they are electrovalent and sometimes
covalent as well.

6. They do not form ions in water but some 6. Usually they form ions in water, so they function
organic acids may form very less ions, which as electrolyte.
function as weak electrolyte.

7. The composition of organic compounds is 7. The composition of inorganic compounds is sim-
complex. ple.

8. There are about 10,000,000 such com- 8. They are about 50,000 such compounds.
pounds.

9. They are coloured and have odour. 9. They are odourless and colourless except some
metals and ammonia.

S me Reasonable Facts

1. Graphite is a good conductor of electricity but diamond is not. It is because in graphite,
carbon forms covalent bonds with only three carbon atoms and there is one free electron
in each carbon atom but diamond does not have one free electron.

218 Modern Graded Science Class 9

2. Carbon forms a covalent compound because it is a non-metal and non-metals from
covalent compounds by sharing electrons.

3. Carbon is a reducing agent because it separates metals from their concerning metallic
oxide when it is heated with the metallic oxides.

4. Organic compounds are non-electrolyte because they are covalent compounds and they
do not dissociate into ions in their molten state and aqueous from.

5. Compounds like Na2CO3, CaCO3, etc. are not organic compounds even though they have
carbon. It is because they are electrovalent compounds and only covalent compounds
having carbon are considered organic compounds [CO2 and CO are covalent and have
carbon but traditionally they are called inorganic).

6. Diamond is the hardest substance known because each carbon atom in diamond is joined
to four other carbon atoms giving rise to a three dimensional rigid and a stable structure.

7. Graphite is used as lubricant because it is soft and non-volatile.
8. Molecular formula of calcium carbide is CaC2 not Ca2C. It is because calcium loses 2

electrons to form the molecule as it is a metal. The electrons are received by two carbon
atoms and they also share three electrons between them.

Things To Know

1. Carbon is a basic non-metal element and generally it is found in all living things.
2. While burning carbon containing substances, they produce sooty smoke.
3. The property of carbon to form long chains or rings by itself linking of their own atoms

through a covalent bond is called catenation.
4. Diamond, graphite and fullerene are crystalline allotropes while coal, coke, charcoal,

lampblack, etc. are amorphous allotropes.
5. An element having different physical properties but nearly chemically same are called

allotrophes and the phenomenon is called allotropy.
6. Graphite is soft and a good conductor of heat and electricity but diamond is the hardest

and it is a bad conductor of heat and electricity.
7. Carbon burns in air and forms CO2 or CO. It also reduces oxygen from metallic oxides.
8. Carbon reacts with steam to form carbon monoxide and hydrogen.
9. The mixture of carbon dioxide and hydrogen gas is called water gas.
10. The branch of chemistry concerned with the compounds of carbon is termed as

organic chemistry.
11. The substances derived from minerals are called inorganic compounds.

Carbon and Its Compounds 219

12. The branch of chemistry concerned with inorganic compounds is called
inorganic chemistry.

13. Graphite is a good conductor but it sublimes at 3730°C.
14. Buckyball is a black, opaque shining allotrope of carbon.
15. Pure buckyball is a bad conductor; it dissolves in benzene and acts as sublimble substance

at 527°C.

Things To Do

Draw structural diagrams of diamond and graphite on a sheet of chart paper. Enlist the
differences between them and display in your classroom.

Test Yourself

1. Multiple Choice Questions (MCQs)

a. Carbon and its reactions are mainly important to the study of:

A. physical chemistry B. analytical chemistry

C. organic chemistry D. inorganic chemistry

b. Which of the following properties is true for organic compounds?

A. Generally they are soluble in water.

B. They have isomers.

C. They have high melting and boiling points.

D. They are generally covalent compounds.

c. The property of catenation is more marked in case of ....

A. carbon B. oxygen C. nitrogen D. hydrogen

d. The specific gravity of graphite is ....

A. 3.5 B. 2.2 C. 5.3 D. 2.3

e. Which element is present in all organic compounds?

A. carbon B. nitrogen C. oxygen D. phosphorous

f. What is the maximum number of covalent bonds an atom of carbon can form?

A. 2 B. 3 C. 4 D. 1

2. Answer the following questions.
a. What is meant by carbon?
b. Write any three sources of carbon.
c. What is organic chemistry?
d. What is allotropy?
e. What is buckyball?
f. What is water gas?

220 Modern Graded Science Class 9

g. Write any two uses of graphite.
h. Write any four amorphous forms of carbon.
i. What is another name of graphite?
j. Write any two properties of carbon.
k. Experimentally prove that sugar contains carbons.
l. What is catenation? Write in brief with an example.
m. What is allotrophy? Write all the allotrophes of carbon.
n. Write any three chemical properties of carbon with balanced chemical equations.
o. Enlist the uses of diamond.
p. What happens when:
i. lead oxide is strongly heated with carbon?
ii. carbon is heated in water vapour?
q. Define
i. organic compound ii. tetravalency iii. inorganic compound iv. caramel

3. Differentiate between b. organic compound and inorganic compound
a. diamond and graphite

4. Give reasons.

a. Carbon forms covalent bonds.
b. Diamond is a bad conductor while graphite is a good conductor of electricity.
c. Graphite is used as lubricant.
d. Diamond is the hardest substance known.

Caramel : burnt sugar used for colouring and adding flavour to food

Lubricant : substance that lubricates

Electrolyte : solution able to conduct electric current, especially in an electric cell
or battery

Mohs : unit which is used to measure hardness of the substances (1 Mohs-10
Mohs)

Soot : lampblack/black substances formed after burning carbon compounds

Tetrahedral : having four faces, four apices and six edges

Vander-waal force : a weak force among particles that quickly vanishes at longer distances

between interacting particles

∆∆∆

Carbon and Its Compounds 221