Blooming science-8-part-2 part press

Chapter Chemistry

11 Matters

Learning Outcomes Estimated Periods: 9+1

On the completion of this unit, the students will be able to:

 show the structure of atom with protons, electrons and neutrons.

 give simple introduction of period table.

 define valency and find valency of first 20 elements with the study of

electronic configuration and molecular formula.

 describe various types of chemical reactions.

 define atomic number and atomic mass and find these.

 define molecular mass and calculate it.

 define chemical reaction and equation.

 write some simple chemical reactions in the form of word and symbolic
equation.

Introduction

Matter is anything that occupies space and has mass and can be perceived by our
physical senses. Modern world of Chemistry is based on the principles given by John
Dalton in 1808. We find in the writings of ancient Greek and Hindu philosophers that
matter is made of very small unalterable particles. They were studied in detail in 19th
century.

The main postulates of John Dalton that laid the foundation of modern era of
Chemistry to germinate in are:

(a) Matter is composed of a number of extremely small particles called ‘Atoms’
which cannot be further subdivided.

(b) Atoms of the same element are identical in all respect but different from those
of other elements.

(c) Combination between atoms take place in small whole number resulting in the
formation of ‘compound atoms’.

(d) The compound atoms of the compound are identical in all respects.

(e) An atom can neither be created nor be destroyed.

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It is noted that the compound atom of John Dalton is synonymous with modern
molecule.

Matter

Living Non-living

Pure Substance Impure Substance

Mixture

Elements Compounds

Homogeneous Heterogeneous
e.g. salt in water e.g. sand in rice

Metals Non-metals Metalloids Noble gases

(a) Atom: An atom of an element is defined as the smallest particle of it that can
react or combine chemically. In other words, an atom is the smallest particle of
an element which can take part in chemical reaction.

(b) Ion: A charged particle (atom, molecule, radical etc.) is called an ion. An atom
is called an ion when it loses or accepts electrons due to chemical reaction.
There are two types of ion.

They are:

(a) Cation (b) Anion

A positively charged atom is called a cation and a negatively charged atom is called
an anion.

Example: H+ Hydrogen ion (a cation)

OH- Hydroxyl ion (an anion)

Cl- Chloride or chlorine ion (an anion)

(c) Molecule: Molecule of an element or compound is the smallest particle of it
that is stable and capable of independent existence. A molecule is made up of
two or more than two atoms.

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(d) Element: An element is the distinct kind of matter which can neither be broken
down into anything simpler by ordinary chemical means nor built up from any
simpler form of matter. There are 109 elements known to us. eg, Hydrogen,
Helium, Oxygen, Gold, Silver, Mercury, etc. You will study in detail about the
elements in coming chapters.

(e) Compound: We have seen many substances around us. Some of them are
elements and others are compounds or mixtures. Two or more than two
elements combine to form a compound and every sample of compound is a
homogeneous mixture. Water is a compound. Water is made up of combination
of hydrogen and oxygen. These two elements are combined in fixed proportion
by weight. Water has the same property, no matter where it is taken from.

A compound is defined as a form of matter, every sample of which is
homogeneous and composed of two or more than two elements combined in
fixed proportion by weight.

Example: Zinc chloride (ZnCl2)
Magnesium chloride (MgCl2)
Zinc sulphate (ZnSO4)
Sodium chloride (NaCl) (common salt)

Chemical compounds are formed due to chemical reactions and the substances
newly formed have different properties than that of original substances.

(f) Mixture: You have seen salt mixed in water, rice-coats mixed in rice, sand
mixed in rice, etc. These two substances though remain together, do not
contaminate each other. Thus, two or more than two substances when brought
together, do not undergo chemical change but simply lie together and retain
their identity, the resulting mass is called a mixture.

Example: Salt solution, sugar solution, etc.

During the formation of a mixture, no chemical reaction takes place and for its
formation no heat may be needed. In a mixture both the substances possess their

identity. That is, they do not lose their properties.

Atomic Structure

Although John Dalton said that atom cannot be

further subdivided, scientists later on developed Proton Electron

devices to study the nucleus and its surroundings. Neutron p+=11 Nucleus
These devices revealed that there are smaller K shell
no=12

particles in atoms. These particles in the atom are L shell

called sub-atomic particles. These particles are M shell
the essential constituent of all atoms.
Atomic structure of sodium
These essential particles of atom were discovered

Blooming Science & Environment Book 8 125

by performing some experiments. These experiments were very costly and they

proved that there are small particles inside the atom which are electrons, protons

and neutrons. Lord Earnest Rutherford discovered the nucleus of atom in 1911. The

nucleus of atom contains protons and neutrons. Neutrons have no charge and possess

the same mass as that of proton. An atomic model of sodium is given in the figure

below: Scan for practical experiment

The above atomic model shows that electrons are revolving
round the nucleus in fixed path called orbit. An orbit can
accommodate fixed number of electrons and the distribution
of electrons was explained by Bohr.

Electron

An electron is negatively charged particle of very small mass. visit: csp.codes/c08e15

Its mass is about 1 th of the mass of an atom of hydrogen and carries a unit
1839

negative charge. An electron is represented by the symbol (e-). An electron is always

revolving round the nucleus of atom in its orbit.

Proton

It is a particle which has a unit positive charge and the mass about the same as that
of hydrogen atom. Protons are represented by (p+) and are present in atoms of all the
elements. Protons are located in the nucleus.

Neutron

A neutron is an electrically neutral sub-atomic particle with a mass almost the same
as that of a proton. It was discovered by Chadwick in 1932. It is represented by (no)
and located in the nucleus.

Subatomic particles Atomic mass Electric charge

Proton 1 a.m.u. (approx) +ve

Electron 1/1839 a.m.u. (approx) -ve

Neutron 1 a.m.u. Nil

1 gm = 6 x 1023 a.m.u

1 Coulomb = 6.25 × 1018 e.s.u. (charge of 6.25 × 1018 electrons)

Nucleus Shell 1 ‘K’ = 2 electrons
Shell 2 ‘K’ = 8 electrons
Every atom has a mass concentrated at Shell 3 ‘K’ = 18 electrons
Shell 4 ‘K’ = 32 electrons
the centre which is very small called p=20 Nucleus
the nucleus. The electrons travel around (p = 20, n =20)
the nucleus in closed orbits with almost n=20

the speed of light and centrifugal force

balances the force of attraction between

them and nucleus. Atomic model of calcium

126 Blooming Science & Environment Book 8

At. no = No. of p+ = No. of eo = 20

At. wt = No. of p+ + No. of no = 40

Atomic Number (Z)

The number of electrons are equal to the number of protons in an electrically neutral
atom. The atom is electrically neutral unit and unless it reacts. When it loses electrons
it becomes positively charged and when it accepts electrons it becomes negatively
charged. The number of electrons or the number of protons in an electrically neutral
atom is called atomic number.

Atomic number = number of protons = number of electrons.

Atomic Weight (A)

In comparison to the mass of protons and neutrons, the mass of electron is negligible.
The protons and neutrons are centralized at the nucleus. The weight of nucleus is
the weight of protons and neutrons. This is called the “atomic weight”. The atomic
weight of an atom is the weight of protons and neutrons or the weight of the nucleus.

Atomic weight = No. of protons + no. of neutrons.

Let the atomic weight be ‘A’, atomic number be ‘Z’ and number of neutrons be ‘N’.

Then, N = A – Z

It is not necessary for an atom to have equal number of protons and neutrons. The
number of protons and neutrons may be different.

Electronic Configuration

The atomic number of each element is unique. You have learnt that atomic number
means number of electrons or number of protons in an electrically neutral atom.
These electrons are revolving round the nucleus in different paths called orbit or
shell. Each orbit has a fixed capacity and number of electrons it can accommodate. It
was explained by Bohr. The distribution of electrons in different orbits is known as
electronic configuration. His scheme is known as Bohr-Bury scheme.

1. The maximum number of electrons in an orbit is given by the formula 2n2 rule,
where n is the number of orbits.

1st orbit, n = 1, no. of electrons = 2n2 = 2 x 12 = 2

2nd orbit, n = 2, no. of electrons = 2n2 = 2 x 22 = 8

3rd orbit, n = 3, no. of electrons = 2n2 = 2 x 32 = 18

4th orbit, n = 4, no. of electrons = 2n2 = 2 x 42 = 32

2. The maximum number of electrons on the outermost orbit shall not have more
than 8 and next to the outermost not more than 18.

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The electronic configuration of first 20 elements in periodic table are given
below.

Scheme of Electronic Configuration

S. Elements Symbol At. No. of Electrons Electronic No. of
No. No. configuration Neutrons

in short

1st 2nd 3rd 4th
Shell Shell Shell Shell

1. Hydrogen H 11 10

2. Helium He 2 2 22

3. Lithium Li 32 1 2, 1 4

4. Beryllium Be 42 2 2, 2 5

5. Boron B 52 3 2, 3 6

6. Carbon C 62 4 2, 4 6

7. Nitrogen N 72 5 2, 5 7

8. Oxygen O 82 6 2, 6 8

9. Fluorine F 92 7 2, 7 10

10. Neon Ne 10 2 8 2, 8 10

11. Sodium Na 11 2 8 1 2, 8, 1 12

12. Magnesium Mg 12 2 8 2 2, 8, 2 12

13. Aluminium Al 13 2 8 3 2, 8, 3 14

14. Silicon Si 14 2 8 4 2, 8, 4 14

15. Phosphorous P 15 2 8 5 2, 8, 5 16

16. Sulphur S 16 2 8 6 2, 8, 6 16

17. Chlorine Cl 17 2 8 7 2, 8, 7 18

18. Argon Ar 18 2 8 8 2, 8, 8 22

19. Potassium K 19 2 8 8 1 2, 8, 8, 1 20

20. Calcium Ca 20 2 8 8 2 2, 8, 8, 2 20

The electronic configuration of elements in the table above are given below.

1. Hydrogen (H)

At. No. = 1 P=1
At. wt. = 1 n=0

Shells K LMN
Electron 1 XXX

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2. Helium (He) K LMN P=2
At. No. = 2 2 XXX n=2
At. wt. = 4
P=3
Shells n=4
Electron
P=4
3. Lithium (Li) K LMN n=5
At. No. = 3 2 1 XX
At. wt. = 7 P=5
n=6
Shells
Electron P=6
n=6
4. Beryllium (Be)
At. No. = 4

At. wt. = 9

Shells K LMN
Electron 2 2 XX

5. Boron (B) K LMN
At. No. = 5 2 3 XX
At. wt. = 11

Shells
Electron

6. Carbon (C) K LMN
At. No. = 6 2 4 XX
At. wt. = 12

Shells
Electron

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7. Nitrogen (N) K LMN P=7
At. No. = 7 2 5 XX n=7
At. wt. = 14
P=8
Shells n=8
Electron
P=9
8. Oxygen (O) K LMN n = 10
At. No. = 8 2 6 XX
At. wt. = 16 P = 10
K LMN n = 10
Shells 2 7 XX
Electron P = 11
9. Fluorine (F) n = 12
At. No. = 9
At. wt. = 19

Shells
Electron

10. Neon (Ne) K LMN
At. No. = 10 2 8 XX
At. wt. = 20

Shells
Electron

11. Sodium (Na) K LMN
At. No. = 11 2 8 1X
At. wt. = 23

Shells
Electron

130 Blooming Science & Environment Book 8

12. Magnesium (Mg) P = 12
At. No. = 12 n = 12
At. wt. = 24
P = 13
Shells K LMN n = 14
Electron 2 8 2X
P = 14
13. Aluminium (Al) n = 14
At. No. = 13
At. wt. = 27 P = 15
n = 16
Shells K LMN
Electron 2 8 3X P = 16
n = 16
14. Silicon (Si) K LMN
At. No. = 14 2 8 4X
At. wt. = 28

Shells
Electron

15. Phosphorous (P)
At. No. = 15
At. wt. = 31

Shells K LMN
Electron 2 8 5X

16. Sulphur (S) K LMN
At. No. = 16 2 8 6X
At. wt. = 32

Shells
Electron

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17. Chlorine (Cl) K LMN P = 17
At. No. = 17 2 8 7X n = 18
At. wt. = 35
P = 18
Shells n = 22
Electron
P = 19
18. Argon (Ar) K LMN n = 20
At. No. = 18 2 8 8X
At. wt. = 40 P = 20
n = 20
Shells
Electron

19. Potassium (K)
At. No. = 19
At. wt. = 39

Shells K LMN
Electron 2881

20. Calcium (Ca) K LMN
At. No. = 20 2882
At. wt. = 40

Shells
Electron

132 Blooming Science & Environment Book 8

The details of first 20 elements

Element Atomic Number of Number of Number of Atomic
Number Protons Neutrons Electrons Mass
H 1
He 1 2 0 1 1
Li 2 3 2 2 4
Be 3 4 4 3 7
B 4 5 5 4 9
C 5 6 6 5 11
N 6 7 6 6 12
O 7 8 7 7 14
P 8 9 8 8 16
Ne 9 10 10 9 19
Na 10 11 10 10 20
Mg 11 12 12 11 23
Al 12 13 12 12 24
Si 13 14 14 13 27
P 14 15 14 14 28
S 15 16 16 15 31
Cl 16 17 16 16 32
Ar 17 18 18 17 35
K 18 19 22 18 40
Ca 19 20 20 19 39
20 20 20 40

Valency

Valency is defined as ‘the combining capacity of an atom for another’. The number
of hydrogen atoms which combine with next element is the valency of that element.
If hydrogen doesn’t react, the valency of such element is compared with oxygen. If
both of these, i.e., hydrogen and oxygen do not react, then its valency is measured
with the reactivity of chlorine with that elements.

The number of valance electrons determine the combining capacity of an atom
and thus valency is equal to the number of electrons taken or given out by an atom
during chemical reaction. Metals give off the electrons. So,

Valency of Metals = number of valance electrons.

Non-metals have tendency to gain electrons. So,
Valancy of non-metals = 8 – number of valence electrons.

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Atoms of an element lose or gain electrons to become stable and they are stable
with octet or duplet structure i.e. with eight electrons in outermost shell other than
1st shell and with two electrons in the first shell.

Valency of some elements are tabulated below.

Valency 1 Valency 2 Valency 3 Valency 4 Valency 5 Valency 6
Monovalent
Hydrogen H Bivalent Trivalent Tetravalent Pentavalent Hexavalent
Potassium K
Sodium Na Oxygen O Nitrogen N Carbon C Nitrogen N Sulphur S

Magnesium Mg Iron Fe Silicon Si Phosphorous P

Calcium Ca Chromium Cr Aluminium Al

Silver Ag Barium Ba Phosphorous P
Copper Cu Zinc Zn

Chlorine Cl Lead Pb
Bromine Br Copper Cu

Iodine I Iron Fe
Mercury Hg Mercury Hg

Variable Valency

Some elements exhibit more than one valency. For example copper has valency 1

or 2. This is called the variable valency.. The variable valency occur because of the

different conditions of chemical reaction. An atom of an element can sometimes lose

more electrons than are present in its outer most shell (Valence shell) i.e. it loses

some electrons from the next to outermost shell (penultimate shell) and hence exhibit

variable valency.

If an element exhibits two different positive valencies then sufix “ous” is attached

at the end of the name of the metal with lower valency and “-ic” for higher valency.

For example, Cuprous - 1 Mercury Mercurous - 1
Copper

(Cu) (Hg)

Cupric - 2 Mercuric - 2

Gold Aurous - 1 Lead Plumbous - 2
(Au) Auric - 3 (Pb) Plumbic - 4
Stannous - 2 Ferrous - 2
Tin Stannic - 4 Iron Ferric - 3
(Sn) (Fe)

134 Blooming Science & Environment Book 8

Radicals

A radical is an atom or group of atoms which maintain their integrity throughout a
series of reactions and can be introduced or expelled from combination without any
change. When it consists of a group of atoms like sulphate (SO4), carbonate (CO3),
hydroxyl (OH), nitrate (NO3), it is called compound radical. Radicals are classified
as basic radical or electropositive radical and acid radical or electronegative radical.

Those elements or radical which collect at the positive electrode during electrolysis
of their salts, are electronegative, i.e. they carry negative charge and therefore move
to the positive electrode. Others which are liberated at the negative electrode are
supposed to carry positive charge and therefore, are called electropositive radicals.

Some of the electropositive and electronegative radicals are tabulated below:

Basic or Electropositive Radicals

Monovalent (+) Bivalent (++) Trivalent (+++) Tetravalent (++++)
Valency 3 Valency 4
Valency 1 Valency 2
Aluminium Al Tin (Stannic) Sn
Ammonium NH4 Barium Ba
Lead (Plumbic) Pb
Gold (Aurous) Au Iron (Ferrous) Fe Iron (Ferric) Fe

Copper (Cuprous) Cu Manganous Mn Gold (Auric) Au

Sodium Na Mercury (-ic) Hg
Potassium K Calcium Ca
Silver Ag Zinc Zn
Mercury Hg Lead
(-ous) (Plumbous) Pb
Copper
(cupric) Cu

Acid or Electronegative Radicals

Monovalent (-) Bivalent (--) Trivalent (---) Tetravalent (----)
Valency 1 Valency 2
Carbonate Valency 3 Valency 4
Bromide Br
O Nitride N Ferrocyonide (CN)6
(Nitrogen)

Chloride Cl Oxide (Oxygen) S Phosphide P

Fluoride F Sulphide (sulphur) CO3 Borate BO3 Carbide (carbon) C

Hydride H Sulphite SO3 Phosphite PO3

Iodide I Sulphate SO4 Phosphate PO4

Acetate CH3COO Silicate SiO3
Bicarbonate HCO3 Manganate
Bisulphate HSO3 Zincate MnO4
Bisulphite HSO4
ZnO2

Blooming Science & Environment Book 8 135

Cyanide CN

Hydroxide OH

Nitrate NO3
Nitrite NO2
Chlorate ClO3

Classification of Elements

There are 100 elements. Out of them 92 are naturally occurring and remaining are
found in the laboratory during nuclear researches. All the elements can be categorized
into three groups. At room temperature and atmospheric pressure (760 mm of Hg),
they are found in solid, liquid or gaseous state. Mercury (Hg), Bromine (Br), Galium
(Ga) and Cesium (Cs) are found in liquid state. Hydrogen (H), Helium (He), Nitrogen
(N), Oxygen (O), Neon (Ne), Fluorine (F), Chlorine (Cl), argon (Ar), Krypton (Kr),
Xenon (Xe) and Radon (Rn) are found in gaseous state. Other elements are found in
solid state.

For the convenience of study, the elements have been divided into two groups.

(a) Metals (b) Non-metals

Metals are generally hard and good conductors of heat and electricity. They are
malleable, ductile and possess a metallic luster. Non-metals, on the other hand, are
not good conductors of heat and electricity. They are not malleable, ductile and do
not possess metallic luster.

Periodic Table

All the properties of element can’t be studied at the same time. So, for the convenience
of study, they are grouped in such a way that the elements having similar chemical
properties fall one after the other. There were many attempts made to produce the
characteristics of elements in a tabular form. It was a Russian scientist Mendeleev
who became successful. According to him “there is a periodic recurrence of elements
having similar chemical properties when they are written in increasing order of their
atomic weights”. He made a periodic table on his scheme and this table has been
modified several times to provide more detail of properties of elements, though, it is
called Mendeleev’s Periodic Table.

Modern Periodic table
Mendeleev’s periodic table was based on atomic weight. In 1931 Henery Moseley
found that the atomic number is the more fundamental property of an element. The
atomic number of an element is equal to number of protons in the nucleus of an atom.

136 Blooming Science & Environment Book 8

Atomic number is also equal to the number of electrons in an electrically neutral
atom.

The atomic number is taken as the basis of classification of elements. This led to the
formulation of Moseley’s periodic law. This means that if the elements are arranged
in order of their increasing atomic number, then elements with similar properties are
repeated after a regular interval.

Modern periodic law states that,’ the physical and chemical properties of elements
are a periodic function of their atomic numbers.

In a periodic table horizontal rows are called the periods and vertical columns
are called groups. Each period has a fixed number of elements. First period has 2
elements - Hydrogen and Helium. Period 2 and 3 have 8 elements each and they
are known as short periods. Period 4 & 5 contain 18 elements and period 6 has 32
elements. These periods are long periods. Period 7 has 6 naturally occurring and 13
laboratory synthesized elements. But it is an incomplete period and a long period.
The details of first 20 elements:

The properties of elements present in a group are similar with each other, whereas
the properties of elements of same period are different. There are eight groups and
seven periods in modern periodic table.

Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8

H (1) He (2)

Li (3) Be (4) B (5) C (6) N (7) O (8) F (9) Ne (10)

Na (11) Mg (12) Al (13) Si (14) P (15) S (16) Cl (17) Ar (18)

K (19) Ca (20)

While studying the properties of the elements in the periodic table, there is a change
from right to left as well as from top to bottom. The elements H, Li, Na & K become
positively charged. The outermost orbit of these elements possesses one electron.

During the time of chemical reaction with other elements, these elements lose the
electron from outermost electron. These elements can react with water and displace
H atom from it.

Similarly, the elements on the 8th Group are inert as they do not react with any other
element.

The elements from 7th Group react with hydrogen and can produce acid. For example,
hydrochloric acid, hydrobromic acid, etc.

With the help of Periodic table, the property of an element can be determined. For
example, hydrogen combines with oxygen to produce water and similarly, hydrogen
combines with sulphur to form hydrogen sulphide.

Blooming Science & Environment Book 8 137

138 Blooming Science & Environment Book 8 MODERN PERIODIC TABLE

eg. for hydrogen, Atomic number - 1 Gas -

Symbol - H Liquid -

Atomic weight - 1.008 Synthetically made -

s Block p Block
Metals Non-metals

Groups 12 13 14 15 16 17 18
Periods IA IIA IIIA IVA VA VIA VIIA O

1 H1 B5 C6 N7 He2
2 1.008 10.881 12.011 14.007 4.003
3
4 Li3 Be4 d Block Al13 Si14 P15 O8 F9 Ne10
5 6.939 9.012 26.982 28.086 30.974 15.999 18.998 20.183
6 3 456 78 9 10 11 12
7 Na11 Mg12 IIIB IVB VB VIB VIIB VIII IB IIB Ga31 Ge32 As33 S16 Cl17 Ar18
22.99 24.312 69.72 72.59 74.922 32.453 35.453 39.948
Sc21 In49 Sn50
K19 Ca20 44.956 Ti22 V23 Cr24 Mn25 Fe26 Co27 Ni28 Cu29 Zn30 114.82 118.69 Sb51 Se34 Br35 Kr36
39.102 40.08 47.9 50.942 50.942 54.938 55.847 58.933 58.933 63.54 63.54 Ti81 Pb82 121.75 78.96 79.904 83.8
Y39 204.37 207.19
Rb37 Sr38 88.95 Zr40 Nb41 Mo42 Tc43 Ru44 Rh45 Pd46 Ag47 Cd48 Bi83 Te52 I53 Xe54
85.47 87.62 91.22 92.906 95.94 99.0 101.07 102.905 106.40 107.87 112.4 113 208.98 127.6 126.904 131.3
La57
Cs55 Ba56 138.91 Hf72 Ta73 W74 Re75 Os76 Ir77 Pt78 Au79 Hg80 Po84 At85 Rn86
178.49 180.943 183.85 186.2 190.2 192.2 195.09 196.967 200.59
132.905 137.34 Ac89 210 210.0 222.0
227 Ku104 Ha105 Unh106 Uns107 Uno108 Une109 Uun110 Uuu111 Uub112
Fr87 Ra88 259 260 261 263 264 266 269 272 277 114 115 116 117 118
223 226

Lanthanides Ce58 Pr59 Nd60 Pm61 Sm62 Eu63 Gd64 Tb65 Dy66 Ho67 Er68 Tm69 Yb70 Lu71 f Block
Actinides 140.12 140.907 144.24 147 150.35 151.96 157.25 158.924 162.5 163.94 167.24 170.61 173.04 174.97

Th90 Pa91 U92 Np93 Pu94 Am95 Cm96 Bk97 Cf98 Es99 Fm100 Md101 No102 Lr103
232.036 231 238.03 237 242 243 247 249 251 254 253 256 259 260

Molecular Formula

The molecular formula of a compound is defined as the symbolic representation that
shows the actual number of atoms of different elements present in one molecule of
the compound. For example, one molecule of ammonia contains one atom of nitrogen
and three atoms of hydrogen. Thus, the molecular formula of the compound, ammonia
is NH3. Similarly, one molecule of water is made up of two atoms of hydrogen and
one atom of oxygen. Thus, its molecular formula is H2O.

Information given by the Molecular Formula

A molecular formula gives the following information:

1. Molecular formula represents one molecule of the substance.

2. It gives the actual number of atoms of each element present in one molecule.

3. It shows the combining capacity of its component elements.

4. It helps to know about the molecular weight of the substance.

Steps of writing molecular formula of the compounds

To write molecular formula, the following steps are usually adapted only when we
know the atomic symbol of elements, symbol of radicals and their valencies.

Step 1: Firstly, the name of compound is written.

Step 2: The symbol of basic and acidic radicals of a compound is written side by
side.

Step 3: The valency of each radical is written on the right upper corner (superscript)
of the symbol.

The valency of one radical is transferred to another radical and is written on the right
hand side bottom corner (subscript). If necessary, L.C.M. of valencies is taken to get
a simple whole number.

Step 4: If a compound radical takes part in the molecular formula, the radical is
enclosed in bracket and the valency number is written on the right side of the
bracket at the bottom of the formula.

For example magnesium sulphate

1. Magnesium Sulphate (Compound)

2. Mg SO4 (Symbols of basic and acidic radical)

Blooming Science & Environment Book 8 139

3. Mg2 SO42 (Valencies)

4. Mg2(SO4)2 (Valencies are exchanged and compound radical

is enclosed in bracket)

5. MgSO4 (L.C.M. is taken)

6. MgSO4 Molecular formula of magnesium sulphate.
Some other examples

1. Calcium nitrate Ca1(NO3)2 Ca(NO3)2
C2a N1O3 Molecular formula of calcium nitrate

Ca1 (NO3)2

2. Carbon dioxide

C4 O2 C2O4 CO2
C2 O4 Molecular formula of carbon dioxide

Molecular formulae of some compounds

S. Compound Molecular S. Compound Molecular
No. Formula No. Formula

1. Ammonium nitrate NH4NO3 26. Magnesium nitrate Mg(NO3)2
NH4Cl MgO
2. Ammonium chloride NH4OH 27. Magnesium oxide
Al(OH)3 MgCO3
3. Ammonium hydroxide AuCl2 28. Magnesium carbonate Mg(HCO3)2
BaO MgSO4
4. Aluminium hydroxide 29. Magnesium bicarbonate Mg(NO3)2
BaSO4 MgCl2
5. Auric chloride Ba(NO3)2 30. Magnesium sulphate Mg(OH)2
CaO HNO3
6. Barium oxide 31. Magnesium nitrate KOH
CaCl2
7. Barium sulphate Ca(HCO3)2 32. Magnesium chloride KNO3
CaCO3 K2SO4
8. Barium nitrate CaSO4 33. Magnesium hydroxide H2SO4
Ca(NO3)2 NaOH
9. Calcium oxide Ca(OH)2 34. Nitric acid
CO2 NaNO3
10. Calcium chloride CaSiO3 35. Potassium hydroxide NaNO2
NaCl
11. Calcium bicarbonate 36. Potassium nitrate

12. Calcium carbonate 37. Potassium sulphate

13. Calcium sulphate 38. Sulphuric acid

14. Calcium nitrate 39. Sodium hydroxide

15. Calcium hydroxide 40. Sodium nitrate

16. Carbondixide 41 Sodium nitrite

17. Calcium silicate 42 Sodium chloride

140 Blooming Science & Environment Book 8

18. Copper oxide CuO 43. Sodium carbonate Na2CO3
19. Copper chloride 44. Sodium bicarbonate NaHCO3
20 Calcium phosphate CuCl2 45. Silver chloride AgCl
21. Ferrous oxide Ca3(PO4)2 46. Silver nitrate
22. Ferric oxide FeO 47. Zinc chloride AgNO3
23. Ferrous sulphate 48. Zinc oxide ZnCl2
24. Hydrochloric acid Fe2O3 49. Zinc bicarbonate ZnO
25. Hydrobromic acid FeSO4 50. Zinc carbonate
HCl Zn(HCO3)2
ZnCO3
HBr

Chemical Reaction

The exchange, combination or decomposition that occurs in the molecules of matters
during a chemical change is called chemical reaction.

Hydrogen + Oxygen → Water

2H2 + O2 → 2H2O

As shown in the above example, the chemical reaction can be represented by word
equation and formula equation.

The properties of matters depend on the organization of their molecules. Although
the same atoms are present in a chemical reaction before and after the reaction,
different types of molecules are formed as a result of the reaction.

Chemical reaction is represented in the form of an equation. The elements or
compounds in which the chemical reaction occurs are written on the left hand side
of an arrow (→) and the elements or compounds that are formed as a result of this
reaction are written on the right hand side of the arrow. The direction of arrow
indicates which are reactants and which are products. For example:

Reactants → Products

The condition of the reaction in which it occurs is sometimes or when necessary
written in short above the arrow.

For example: Water electrolysis Hydrogen + Oxygen

Mercuric Oxide heat Mercury + Oxygen

Potassium Chlorate heat Potassium chloride + Oxygen

Chemical Equation

A chemical equation may be defined as the symbolic representation of a chemical
reaction in terms of symbols and formulae. If the chemical equation is written in
terms of symbols and molecular formulae, then it is called formula equation. A
formula equation may be unbalanced or balanced. In the unbalanced equation, the

Blooming Science & Environment Book 8 141

number of atoms of one or more elements on two sides is not equal. It is also called
skeleton equation. This equation can be balanced by comparing the number of atoms
on two sides. The equation is called balanced equation only when the number of
atoms of the different elements on the two sides becomes equal.

To understand the above fact, the following chemical equation is taken as an example.
When a mixture of hydrogen and chlorine is placed in the sunlight, they react together
and form hydrogen chloride.

Hydrogen + Chlorine → Hydrogen chloride

Reactants Products

H2 + Cl2 → HCl (Formula equation/Unbalanced equation)
H2 + Cl2 → 2HCl (Balanced equation)
In this chemical equation, the number of hydrogen and chlorine is equal to each side,
Thus, this equation is called balanced equation.

Balancing the Chemical Equations

The following rules should be kept in mind to balance the chemical equation:

1. First of all write the word equation clearly.

2. The symbol and molecular formula of each reactants and products are written
in the form of an expression. The written expression is called skeletal or
unbalanced equation.

3. The number of atoms of different elements is counted on each side of the
chemical equation.

In course of counting the number of atoms to balance an equation, the following
points should be noted:

a. The number, which is written on the right lower corner of an atom, is for
that atom only. For example, AlCl3 has 1Al and 3Cl atoms.

b. The number, which is written on the right side lower to the bracket is for
all those atoms enclosed in the bracket. For example, Ca(OH)2 has 1Ca,
2O and 2H.

c. The number of coefficient written in front of a molecule belongs to all
the number of atoms of molecule. For example, 2Ca(OH)2 has 2Ca,
(2 × 2)O and (2 × 2)H.

4. Atoms of the biggest molecule of the chemical equation are balanced first,
whereas the hydrogen and oxygen atoms of the equation are balanced at the
end. In course of balancing the equation, the molecule is always multiplied by
required number.

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5. Indicate the physical state of the reactants and products by using s for solids,
l for liquids, g for gases and aq for solution in water.

Some examples of Chemical Equations

1. Magnesium + Nitrogen → Magnesium nitrate [Word equation]

Mg + N2 → Mg2N2 [ Skeleton equation]
3Mg + N2 → Mg3N2 [Balanced equation]
(s) (g) (s)

2. Magnesium oxide + Water → Magnesium hydroxide [Word equation]

MgO + H2O → Mg(OH)2 [Balanced equation]

(s) (l) (aq)

3. Potassium chlorate ∆ Potassium chloride + Oxygen [Word equation]

KClO3 ∆ KCl + O2 [Skeleton equation]
[Balanced equation]
2KClO3 ∆ 2KCl + 3O2

(s) (s) (g)

4. Iron + Copper sulphate → Copper + Iron sulphate [Word equation]

Fe + CuSO4 → Cu + FeSO4 [Balanced equation]
(s) (aq) (s) (aq)

5. Hydrochloric acid + Sodium hydroxide → Sodium chooride + Water

[Word equation]

HCl + NaOH → NaCl + H2O [Balanced equation]

(aq) (aq) (aq) (l)

Molecular Weight

The sum of the atomic weights of all the atoms of same or different elements present
in a molecule is called molecular weight. In other word, molecular weight is defined
as the sum of the atomic weights of elements in molecular formula written according
to their valencies. For example,

The molecular weight of methane (CH4) = 1 × 12 + 4 × 1

= 12 + 4 = 16 a.m.u.

Note: Molecular weight of carbon (C) is 12 and hydrogen (H) is 1

Blooming Science & Environment Book 8 143

Similarly,
Molecular weight of carbon dioxide (CO2) = 1 × 12 + 2 × 16
= 12 + 32 = 44 a.m.u.

Molecular weight is simply a number. It does not have any unit of mass. The
molecular weight of a substance (elements or compounds) expressed in terms of
grams is termed as its gram-molecular weight. For example, gram molecular weight
of carbon dioxide is 44 grams because its molecular weight is 44. If 44 gm (1 mole)
of CO2 is taken it contains 6.02 × 1023 molecules which is called Avogadro’s number
(NA).

Main Points to Remember

1. The smallest particle of an element is atom. Proton, neutron and electron are
sub-atomic particles.

2. When two or more elements combined in a fixed ratio, a new substance is
formed called compound.

3. Physical change is temporary change and chemical change is permanent
change.

4. Symbol is defined as the shorthand sign of the full name of an element.

5. Symbol of an element is made up of one or two letters.

6. If symbol has two letters, the first letter is always written in capital and the
other one in small letter.

7. Electropositive radicals are cations or basic radicals and electronegative
radicals are anions or acid radicals.

8. The combining capacity of an element or radical is called valency of that
element or radical.

9. Valency may be variable in some cases. Elements with lower valency end with
‘ous’ and those with higher valency end with ‘ic’.

10. The symbolic representation of a molecule is called molecular formula.

11. Molecular formulae are written by using symbols and valencies.

12. The elements are arranged in row and columns in a table by certain rules called
periodic table. The rows are groups and columns are periods.

144 Blooming Science & Environment Book 8

13. The representation of chemical reaction in the form of chemical reaction is
called chemical equation.

14. Reactants are those substances which take part in chemical change.

15. Products are those new substances that are formed as a result of the chemical
change.

16. The representation of a chemical change by writing the full names of the
reactants and products is called word equation.

PRO J ECTWORK

1. Make a chart showing symbols and valencies of basic and acid radicals. Paste
in the front of study table. Study them in free times.

2. Draw atomic model from 1 to 20 elements with their symbols, valency and
electronic configuration on a chart paper and paste in your classroom.

Exercise

1. Answer the following questions.

a. What is matter? Write its properties.

b. What are symbol and valency?
c. What are the basis of making symbols? Give any four examples of each.
d. What is meant by H2 and 2H?
e. What is radical? What are the electropositive radicals? Write with

examples.
f. The molecular formula of water is H2O. What do you meant by it?
g. Define periodic table. What are groups and periods?
h. What is Mendeleev’s periodic law?
i. State modern periodic law.
k. What is electronic configuration? Show electronic configuration of Na,

Mg, Cl and K.
2. Define.

a. Ions b. Groups c. Periods d. Radicals e. Word equations

3. Write the symbols and valencies of the following radicals and mention
whether they are basic radicals or acid radicals.

a. Ammonium b. Silicate c. Plumbic d. Carbon

e. Zinc f. Aluminium g. Chlorate h. Peroxide

i. Silver j. Barium k. Nitrite l. Phosphate

Blooming Science & Environment Book 8 145

4. Write the molecular formula of the following substances in the given

pattern. e.g. Calcium nitrate = Ca2(NO3)1 = Ca(NO3)2

a. Ferrous oxide b. Ferric oxide c. Silicon chloride

d. Silicon oxide e. Barium nitrate f. Plumbic phosphate

g. Sodium peroxide h. Calcium bicarbonate i. Silver nitride

j. Potassium sulphate k. Aluminium carbonate l. Ammonium sulphate

m. Plumbous silicate n. Calcium hydroxide o. Sodium carbonate

5. Write the molecular formulae of the following compounds directly.

e.g. Calcium nitrate - Ca(NO3)2 c. Mercuric oxide
a. Mercurous sulphate b. Manganic bisulphate

d. Magnesium oxide e. Sodium oxide f. Cupric silicate

g. Ammonium sulphate h. Magnesium hydroxide i. Cuprous carbonate

j. Zinc peroxide k. Potassium chlorate l. Sulphuric acid

m. Sodium nitrite n. Limestone. o. Nitric acid

6. Complete the following chart.

Acid Oxide Hydroxide Peroxide Chloride Chlorate Sulphite Sulphate Silicate
Radical→
CaO MgO2 Mn(ClO3)3
Basic
Radical ↓
Calcium
Magnesium
Sodium
Aluminium
Plumbic
Manganic
Ammonium
Aluminium

7. Translate the following word equations into the form of balanced equation.
a. Aluminium + Hydrochloric acid → Aluminium chloride + Hydrogen
b. Iron + Oxygen → Ferric oxide (Rust)
c. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
d. Magnesium + Nitrogen → Magnesium nitride
e. Sulphuric acid + Potassium hydroxide → Potassium sulphate + Water

146 Blooming Science & Environment Book 8

f. Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
g. Calcium + Nitrogen → Calcium nitride
h. Calcium + Water → Calcium hydroxide + Hydrogen
i. Hydrogen + Oxygen → Water
j. Methane + Water vapour → Carbon monoxide + Hydrogen
k. Carbon + Oxygen → Carbon monoxide
l. Sulphur + Oxygen → Sulphur dioxide
m. Calcium bicarbonate Heat Calcium carbonate + Water + Carbon dioxide
n. Magnesium + Carbon dioxide →Magnesium oxide + Carbon
o. Carbon dioxide + Water → Carbonic acid
p. Ammonia + Water → Ammonium hydroxide
q. Ammonium hydroxide + Sulphuric acid → Ammonium sulphate + water
r. Ammonia + Hydrochloric acid → Ammonium chloride

Glossary

Aggregate : a total number or amount made up of smaller amount that are
collected together.
Inert
Aqueous (aq) : inactive, noble
Expression
: describing of a solution in water

: things that people say.

Blooming Science & Environment Book 8 147

Chapter Separation of Mixture

12

Learning Outcomes Estimated Periods: 3+2

On the completion of this unit, the students will be able to:

 define mixture and the types of mixture.

 describe and demonstrate chromatography and distillation.

 write in brief about the different methods of separation of mixture.

Introduction

A mixture is a combination of two or more substances that are not chemically united
and do not exist in fixed proportions to each other. Impure substances are made up of
two or more than two pure substances mixed together in any proportion. They do not
undergo chemical change but simply lie together and retain their identity. Therefore,
the impure substances are called mixture. For example salt in water-salt solution,
mud in muddy water, copper sulphate in copper sulphate solution, mixture of water
and alcohol, etc. The mass formed when two or more than two substances are mixed
together in any proportion by weight is called mixture.

A mixture is a substance or mass in which two or more than two substances when
brought together do not undergo chemical change but simply lie together and retain
their identity. For example, sugar solution, salt solution, soda, milk, blood, etc.
The mixture may be homogeneous or heterogeneous. Homogeneous mixtures are
those in which the solute component molecules cannot be seen through naked eye.
In heterogeneous mixtures, the one or both the components present may be seen
through naked eye because they are big in size.

The components of a mixture can be separated to get pure substances. The separation
of the components of mixture depends on the principle that “different substances
have different properties.” The process by which the components of a mixture are
separated from each other is called separation of mixture. In the lower classes, the
following methods of separation of mixtures are studied:

1. Sublimation: This method is used to separate sublimates like camphor, iodine,
etc. from their respective mixture in which solid changes into gas on heating
and vice-versa.

148 Blooming Science & Environment Book 8

2. Decantation and Sedimentation: These methods are used to separate
the components of heterogeneous mixture. For example, mud and sand are
separated from the mixture of muddy water and sand water respectively.

3. Evaporation: This method is used to separate the components of homogeneous
mixture like salt from water in salt solution.

4. Distillation: This method is used to separate the components of homogeneous
solution like water and alcohol from water-alcohol mixture.

5. Magnetic Separation: This method is used to separate the magnetic materials
like iron, cobalt, etc. from their respective mixture. For example, iron filings
are separated from a mixture of iron filings, sodium chloride and sand.

6. Filtration: This method is used to remove insoluble substances from a mixture
by the use of filter paper. For example sand is separated from the mixture of
sand and water.

Uses of Mixture

The mixtures are used in different areas of daily life. We prepare many mixtures in
the preparation of food and beverages. In constructing houses, roads and bridges also
different mixtures are used in different ways. Some of the application and uses of
mixture are given below.

(a) Cement, sand, concrete and water is mixed for lintering (dhalan) of houses and
roofs.

(b) The mixture of sand, cement and water is used in plastering walls and joining
bricks.

(c) Grains of tea, water and milk is mixed to make tea.

(d) Plants take different nutrients in the form of mixtures from the soil.

(e) In the food and beverages, nutrients are mixed. We get energy from the nutrients
mixed in the food and beverages.

In this lesson, we will study about some more methods of separation of mixture.

Chromatography

Chromatography is made of two words “chroma” meaning “colour” and “graphein”
meaning “to write”. So chromatography means “colour writting”. The Russian
botanist, Micheal Tsvet invented chromatography in the beginning of the 19th century
by which pigments (colours) are separated. Nowdays, chromatography is applied
to separate and identify for separating the components of a mixture by passing it
through a column or sheet of an adsorbing material. The principle of this process
depends upon “the different components of mixture are absorbed into different

Blooming Science & Environment Book 8 149

extends and move down the column at different rates.” This method is applicable to
those mixtures in which the particles of components are very simple.

To understand the fact, let’s put a drop of ink on a filter paper or on a chalk. We will

notice that the ink on the chalk or on the filter paper is dark at the centre and light at

the edge. Can you say, why? This is due to different rates of movements of the ink by

the moving water which causes the separation. There are various techniques of

chromatography; they are:

1. Paper chromatography Scan for practical experiment

2. Adsorption chromatography

3. Gas liquid partition chromatography

Here, we will study about the first two techniques of visit: csp.codes/c08e16
chromatography.

Paper Chromatography

It is a technique in which a filter paper or chromatography paper is taken as an
adsorbent material for analyzing mixture by chromatography.

Activity

To separate the different colours of ink by using paper chromatography.

Materials required: a few pieces of filter paper, petri dish, water, black ink

Method:

1. Make a hole in the centre of a filter paper and insert a role of another filter
paper in the hole.

2. Put a drop of black ink near the hole as shown in the figure.

3. Adjust the filter paper above a petri dish with water in such a way that the
roll of the filter paper is immersed partially in it.

4. Leave it for 1 to 2 hours then observe it.

Filter paper Roll of filter paper

Hole Filter paper with
A drop of black ink spot of black ink

Water

Fig: Chromatography
150 Blooming Science & Environment Book 8

Activity

To separate the different colours of mixture of blue and red ink.
Materials required: a strip of filter paper, red and blue ink, vessel, stick
Method:
1. Take a mixture of blue and red ink.
2. Adjust a strip of filter paper in such way that the filter paper must not touch

the vessel as shown in the figure.
3. Leave it for 1 to 2 hours then observe it.

Stick

A strip of Red
filter paper

A spot of ink Blue
Vessel Water

Fig: Paper chromatography

Observation
You will see the rings of blue and red colours on the filter paper.
Conclusion
The activity helps to separate the different colours on mixture of ink.

Solvent

Adsorption Chromatography Coloured zone

It is based on the principle that a certain adsorbent Adsorbent
can absorb different substances to different
extents.” When a solution containing two or more Coloured zone

than two dissolved substances is to be separated, it Glass wool
is allowed to pour into vertical glass tube packed

with finely divided adsorbent like alumina. The

colours of dissolved substances of a solution are

separate in the form of banks. Chalk, silicate gel or Solvent
magnesium oxide also can be taken as adsorbing

materials in a vertical glass tube instead of alumina.

Fig: Adsorption chromatography

Blooming Science & Environment Book 8 151

Distillation

The conservation of liquid into vapour on heating and then cooling the vapour
changes back into liquid is called distillation. This method is used to separate the
components of a mixture whether the components are liquids or one is soluble solid
and the other is liquid. It is also used to separate the components of a mixture of two
miscible liquids having different boiling points. In other words, distillation is based
on the process of evaporation of a liquid followed by condensation of the vapour.

Activity

To separate salt from salt water solution Thermometer

Material required: Stand, a burner, a Liebig’s
tripod stand, condenser, thermometer, round condenser
bottomed flask, distillation flask

Methods RB flask Distillate
Mixture
1. Take a distillation flask and fill half
portion of it with salt solution and set Burner
up the apparatus as shown in the figure.

2. Heat the flask till the water boils. Fig: Distillation

3. Observe what happens. What will be left in the distillation flask?

The vapour produced during boiling of water is allowed to pass through the inner
tube of the condenser while heating. When the vapour passes through the condenser,
it condenses into tiny droplets of water which is collected in receiver.

The water collected in the receiver is called distillate. The distillate refers to the
vapour which has condensed to give back the liquid. When all the water is boiled
dry, the dissolved salt remains behind in the flask as residue. The distilled water is
very pure.

Fractional Distillation

A homogeneous mixture of two or more liquids can be separated by fractional
distillation method. For this boiling points of different liquids are determined and
such substances are separated from each other. In this method the liquid having lower
boiling point is separated first by vaporisation and condensation process leaving
behind the liquid with higher boiling point. This process is carried out by using a
fractional column. This method is mainly used for the purification of petrol and other
petroleum from mineral oil.

152 Blooming Science & Environment Book 8

Fig: Fractional distillation

Main Points to Remember

1. There are two types of mixtures. They are homogeneous and heterogeneous
mixture.

2. The conversion of liquid into vapour on heating and then cooling the vapour
changes back into liquid is called distillation.

3. Small crystals are obtained when the solution is cooled quickly and big crystals
are obtained when the solution is cooled slowly.

4. Chromatography is a method of separation of colours/pigments from a solution.
5. Chromatography is of many types like: paper chromatography, adsorbent

chromatography and gas liquid partition chromatography.
6. Chromatography is based on the principle that speed of different size of

particles in the same medium is different.

PRO J ECTWORK

Take some petals of roses flower and grind them. Extract the solution and use it
in paper chromatography and note the different colour bands in the paper.

Blooming Science & Environment Book 8 153

Exercise

1. Define the following terms.

a. Sublimation b. Heterogeneous mixture c. Saturated solution

d. Solvent e. Distillation f. Homogeneous mixture

2. Write the steps of the separation of the following mixtures:

a. Iron dust + sand b. Iron dust + sand + salt

c. Iron dust + sand + salt + camphor d. Ink form a solution

e. alcohol + water f. sugar + sand + water

3. What is mixture? Write uses of mixture.

4. Write the procedure of paper chromatography.

5. What is chromatography? Write in short about adsorbent chromatography.

6. Which method is used to separate the following mixtures:

a. Water and alcohol b. Salt from water and salt

c. Iodine and sand d. Cream from milk

e. Pure salt from rock salt f. Red and blue inks from a solution

7. If two different types of particles have the same speed in a medium, is
chromatography possible? Write with reason.

8. Write the differences between:

a. Evaporation and distillation b. Filtration and chromatography

9. Write the advantage of using chromatography.

10. Which process is used to.

a. Separate colouring matter in ink? b. Dry clothes in a washing machine?

c. Remove the suspended particles in a solution?

d. Make pure salt from rock salt?

154 Blooming Science & Environment Book 8

11. Draw a labelled diagram of.
a. Paper chromatography b. Distillation

Glossary

Adsorbent : a substance on the surface of which a surface is adsorbed.

Adsorption : the formation of a layer of gas liquid or solid on the surface of a
solid or of a liquid.

Platelets : a minute disc shaped blood cell of mammal formed in red bone
marrow and having no nucleus

Mother liquor : it refers to the solution that is left after the formation of crystals
during crystallization.

Blooming Science & Environment Book 8 155

Chapter

13 Metals and Non - metals

Learning Outcomes Estimated Periods: 7

On the completion of this unit, the students will be able to:

 differentiate metals and non-metals in period table.

 introduce and tell the properties and uses of some metals and non metals like
Iron, Aluminium, Copper, Silver, Gold and Carbon.

Introduction

At present 118 elements are known. On the basis of certain important properties,
these elements are divided into two groups: metals and non-metals. A large number
of elements (about 80%) are metals.

Copper was the first metal to be used by human. Human beings have been using
different kinds of metals for different purposes. Metals are so vital to us that it is
unthinkable to live without them. They are essential for the construction of houses,
transportation, communication, electricity, household articles, scientific instruments,
weapons, automobile parts, coins, etc.

Metals like gold and silver are rust free. They are used in making valuable ornaments.
Most of the metals do not exist in the native form, with the exception of few like gold
and platinum.

Position of Metals in the Periodic Table

All metals are placed in the left and central part in the periodic table. The elements
with highly metallic properties are on the extreme left of the periodic table. Group IA
is of highly reactive metals called alkali metals and group IIA is called alkaline earth
metal. Metals between IIA and IIIA are transition metals. In groups IIIA, IVA and VA,
the metallic characters of the metals increase down the group. For example, in group
VA, the first and second members (Nitrogen and Phosphorus) are non-metals, third and
fourth (Arsenic and Antimony) are metalloids and the fifth one (Bismuth) is a metal.
They form the borderline between the metals and non-metals in the periodic table.

156 Blooming Science & Environment Book 8

Position of Metals in Periodic Table.
IA IIA IIIA IVA VA VIA VIIA O
H
Li Be B
Na Mg Al Si
K Ca Ga Ge As
Rb Sr In Sn Sb Te
Properties of Metals
The following are the general properties of metals:
1. Most of the metals are found in the solid state except a few like mercury and

cesium.
2. Metals are generally hard.
3. They can produce metallic clink sound.
4. They posses metallic luster.
5. They can be beaten into thin plate. This property of metal is called malleability.

The metals that show this property are called malleable.
6. The metals can be drawn into wires. This property of metals is called ductility

and the metals are ductile.
7. Metals are the good conductors of heat and electricity.
8. Generally metals have high boiling and melting points.

Uses of Metals
1. Metals like gold, silver and copper are used for making jewellery and medals.
2. They are used for making coins.
3. They are used for making various articles like bolts, pipes, chains vehicles and

railway track.
4. They are used in making agricultural appliances, weapons and many other tools.
5. They are used for making utensils, frames, electrical goods, etc.
6. They are used for making many useful alloys such as brass and bronze, etc.

Blooming Science & Environment Book 8 157

Non-metals
Non-metals are mostly soft in nature. They do not show the property of malleability
and ductility. They do not possess metallic luster. Usually they are not good
conductors of heat and electricity. They are found in solid, liquid or gaseous state.
Carbon, oxygen and nitrogen are some examples of non-metals. Following are the
properties of non-metals.
1. Non-metals are found in all three states, i.e. solid, liquid and gaseous at ordinary

temperature.
2. They are generally soft in nature
3. They do not produce any metallic clink sound.
4. They are not malleable.
5. They are not ductile.
6. They are bad conductors of heat and electricity.
7. They have usually low melting and boiling points.
8. They are dull and cannot be polished.

Metalloids
There are certain elements which have some properties that are typical of metals
as well as some properties that are typical of non-metals. Such elements are called
metalloids.

Metalloids possess the following characteristics:
1. They are poor conductor of heat an electricity.
2. They possess metallic lustre.
3. They are neither malleable nor ductile
4. They form alloys.
For example, antimony (Sb) has a metallic appearance but it is brittle like non-
metals. Metalloids form the dividing line between metals and non-metals. Boron
(B), Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb) and Tellurium (Te)
are metalloids.

158 Blooming Science & Environment Book 8

Differences between Metals and Non-metals

A detailed comparison of properties of metals and non-metals is given in table given
below.

Metals Non-metals
1. At ordinary temperature, metals are 1. At ordinary temperature, non-
metals are found in all three states
usually solids. Mercury (Hg) and Bromine (Br) is liquid non-metal.
Gallium (Ga) are liquid metals. Most non-metals have low melting
2. Metals usually have high melting 2. and boiling points. The exceptions
and boiling points. But lithium, are carbon, boron and silicon which
sodium and potassium, which melt are solids with very high melting
and boil at low temperatures points.
Non-metals are non-malleable.
3. Metals are usually malleable. Gold 3. They are usually brittle and become
and silver are among the most powder when beaten.
malleable metals. The exceptions
are sodium, potassium, mercury Non-metals are usually non-ductile.
etc. So they can’t be drawn into thin
wires.
4. Metals are usually ductile. Tungsten 4. Non-meals are usually light and soft.
wire can be drawn so fine as to be But carbon in the form of diamond
invisible to the naked eyes. is the hardest substance known. It
has high density.
5. Metals have high density and are 5. Non-metals are usually bad
hard. Although sodium metal is so conductors of heat and electricity.
soft that it can be cut with knife. But graphite is a good conductor of
electricity.
6. Metals are good conductors of heat 6. Non-metals usually do not have a
and electricity. metallic luster. However, graphite
and iodine have a typical metallic
7. Metals usually have a metallic 7. luster.
luster. They do not form alloys. But carbon
is used in making steel (alloy).
8. Most metals form alloys. 8.
Nichrome is an alloy of nickel and Non-metal atoms generally contain
chromium. 4 or more then 4 valence electrons.

9. Metal atoms generally contain 1, 2, 9.
or 3 valence electrons.

Blooming Science & Environment Book 8 159

Some Important Metals

Iron

Iron is known from very ancient times of human civilization. It is the second most
abundant metal occurring in the earth’s crust.

Symbol: Fe Atomic No: 26

Atomic Wt: 55.84 Valency: 2 and 3

Electronic configuration of iron

Shell K L MN

Electrons 2 8 14 2

Occurrence

Iron is very rarely found in free state but it occurs in nature in combined form. It is
found in the body of living organisms. In blood it occurs as a part of hemoglobin. It
is richly found in different ores.

Hematite is very chief ore from which most of the iron is extracted. Hematite ore
contains maximum amount of iron (about 72.5%) and abundantly found in the
nature.

Physical properties of Iron
1. Pure iron is a silvery white and lustrous metal.
2. Its specific gravity is 7.86.
3. Iron melts at about 1500ºC and boils at about 2500 ºC.
4. Iron becomes non-magnetic substance when its temperature is more than 770 ºC.

Uses of Iron
1. Iron is used for making rods, pipes, chains, vehicles, railway track, etc.
2. It is used for the manufacture of agricultural appliances, weapons and many

other tools.
3. It is used in the manufacture of steel.
4. It is used in making household utensils.
5. It is used as catalyst in different chemical reactions.

Aluminum
Aluminum was first isolated by Wholer in the year 1827. It is the third most abundant
element in the earth’s crust. It is a bluish white metal with a bright luster.

160 Blooming Science & Environment Book 8

Symbol : Al Atomic No : 13
Atomic Weight : 27 Valency : 3

Electronic Configuration

Shell K L M
No. of electrons 2 8 3

Occurrence

Aluminum is not found in free state. But, in the combined state, it is abundantly
found in the earth’s crust and constitutes abut 7.3% of it.

Bauxite is the most important and readily distributed ore in the earth’s crust.

Physical Properties
1. Aluminium is a bluish white shining metal.
2. It is light and its specific gravity is 2.7.
3. Its melting pint is 660 ºC and boiling point is 1800 ºC.
4. It is a good conductor of heat and electricity.

Uses of Aluminium

1. Aluminium is used for making utensils, frames, electrical goods, construction
materials, etc.

2. Its alloys are used for making sailboats, aircraft, automobiles, etc.

3. It is used for making aluminium foil for wrapping food, cigarette, pharmaceutical
products, etc.

4. It is used for making electric wire.

5. It is used of making coins.

6. It is used for making alloys.

7. It is used for making silvery paints.

Copper

Copper has been known since pre-historic times. Its Latin name is Cuprum, which
has been derived from the Island of Cyprus.

Atomic symbol : Cu Atomic No : 29

Atomic wt. : 63.57 Valency : 1 and 2

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Electronic Configuration of Copper

Shell K L M N
No. of electrons 2 8 18 1

Occurrence

Copper occurs in free as well as in combined states in the nature. In free state or in
native state, it is found in small amount.

Copper pyrite is the major source of copper, from which copper is mainly extracted.

Physical Properties of Copper
1. Copper is a reddish brown metal with a metallic luster.
2. It is a good conductor of heat and electricity.
3. Its specific gravity is 8.95.
4. Its melting point is 1083ºC and boiling point is 2350 ºC.

Uses of Copper
1. Copper is used for making electrical goods and cables.
2. It is used for making coins, jewelry, decorative objects and domestic utensils.
3. It is used in preparation of many useful alloys such as brass.
4. It is used in electroplating.
5. It is used for the manufacture of dyes, pesticides, etc.

Silver

Silver is known as coinage metal. It has been known to mankind since ancient time.
The symbol Ag of silver is derived from the Latin word Argentums. It is soft lustrous
white metal.

Symbol : Ag Atomic No :47

Atomic weight : 107.88 Valency :1

Electronic Configuration of Silver

Shell KL M N O

No. of electrons 2 8 18 18 1

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Occurrence

Silver occurs in free state as well as in combined state. The important ores of silver
is Argentite or silver glance.

Physical Properties
1. Silver is a white lustrous metal.
2. Its specific gravity is 10.5
3. Its melting point is 960 ºC and boiling point is 1955 ºC.
4. It is a good conductor of heat and electricity.

Use of Silver
1. Silver is used to make coins, jewelry and decorative articles.
2. It is used in the preparation of silver salts and medicines.
3. It is used for silvering mirror and for filling teeth.
4. Silver bromide is used in photography.
5. It is used in electroplating or silver plating.

Gold

Gold is known as coinage metal and mankind has known it since ancient time. The
symbol Au for gold is derived from the Latin word ‘Aurum’.

Symbol : Au Atomic No : 79

Atomic weight : 197.2 Valency :1and 3

Electronic Configuration

Shell K L M N OP
8 18 32 18 1
No. of electrons 2

Occurrence

Being known as a noble metal, it usually occurs in native state either mixed with
quartz in rocks (reef gold) or in alluvial sand.

Physical Properties of Gold
1. Gold possesses a lustrous yellow colour.
2. It has melting point 1063ºC and boiling point 2610ºC.
3. It is heavy metal with a specific gravity of 19.3.
4. It is good conductor of heat and electricity.

Blooming Science & Environment Book 8 163

Uses of Gold
1. Gold is used for making jewelry, coins and medals.
2. It is used for electroplating.
3. It is used for making many gold salts, such as auric chloride which is used in

electroplating and photography (black and white) as a toning agent.
4. It is used for making gold leaf electroscope.
5. It is used for preparing alloys.

Carbon
Carbon is a non-metal that has been known since ancient time in the form of coal
and charcoal. The word carbon is derived from the Latin word ‘carbo’ which means
charcoal or soot. In fact, Carbon is found in nature in various forms like coal, charcoal,
graphite, diamond. Carbon is also found in combined state in the form of compound
like carbndioxide of air, protein, carbohydrates and fat of living being also.
The symbol of carbon is C. Its atomic number is 6 and atomic mass is 12. It has four
valence electrons. Its valency is 4.

Sources of Carbon
The following are the major sources of carbon:
1. Carbon dioxide of air
2. Petroleum matter and natural gases.
3. Organic compounds like carbohydrates, proteins, fats, etc.
4. Minerals and rocks like limestone.

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 12. Carbon is the first member of group-IV
A elements.

P=6
n=6

Since atomic number is 6, it has six electrons in its orbits. These six electrons are
arranged in different energy level of carbon atoms as shown below.

164 Blooming Science & Environment Book 8

Orbit K L
No. of electron 2 4

This electronic configuration shows that carbon has four valance electrons. It shows
that carbon can attain a stable configuration like that of inert gases in the following
ways:

1. It can lose four valence electrons.

2. It can gain four electrons in its valence shell.

3. It can share its four valence electrons with other atoms.

The energy consideration, however, suggests that loss or gain of four electrons by a
carbon atom is not possible. Therefore carbon cannot form electrovalent bonds with
other atoms. Then only possibility to attain stable electronic configuration is that
a carbon atom should share its 4 valence electrons with other atoms. So, it forms
covalent bonds and its compounds are of covalent nature. For example, methane
(CH4).

Physical Properties of Carbon

Carbon is a non-metal. It can exist in different physical forms. Diamond, graphite,
charcoal, coal, etc. are the carbon which appear in different physical modification
but chemically they are all the same. These different forms of the carbon are called
allotropes. This property of an element by which it exists in different physical
modifications, but chemically almost same is termed as allotropy and the different
forms of the same element are called allotropes.

Cabon is known to exist in two distinct allotropic forms. They are:

1. Crystalline forms: diamond and graphite.

2. Amorphous forms: coal, charchoal, animal charcoal, coke, lampblack (soot), etc.

a. Diamond: Diamond is considered as the purest form of carbon. It is the
hardest, transparent and colourless crystalline substance, which is naturally
formed. It is insoluble in all ordinary solvents. There is no free electrons in
diamond, therefore, it is a bad conductor of electricity. Diamond is used as
precious gems in jewelers because of its ability to reflect light.

b. Graphite: Graphite is another crystalline allotropes of carbon. It is also known
a plumbago or black lead. It is soft, slippery to touch, opaque and dark grey
solid. It is also found in crystalline form. It is a good conductor of electricity
because of one free electron with each carbon atom of the graphite layers. It
posses a metallic lustre despite being a non-metal. It is used in pencil. It is used
as a dry lubricant as well.

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Differences 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 crystalline 2. It is a opaque, dark grey and

substance with bright appearance. shiny substance.

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

electricity. and electricity.

4. Its specific gravity is 3.5. 4. Its specific gravity is 2.2.

Alloys

Alloys can be made by mixing two or more than two metals and non-metal (s)
or metals in liquid state. After cooling, the liquid changes into solid mass. Such
solid mass is called alloy. Thus, an alloy is defined as a homogenous mixture of
two or more metals and non-metals. For example, brass is an alloy of copper and
zinc. Stainless steel is an alloy of iron, chromium and carbon, etc. Alloys have the
following properties:

1. Generally alloys are harder than their components.

2. They are good conductors of heat and electricity.

3. They are malleable and ductile.

4. Generally they are brittle in nature.

5. They have low melting point.

6. Alloys increase the strength of metals.

Main Points to Remember

1. Metals are placed in the left and central part in the periodic table.
2. Non-metals are placed in the right side of the periodic table.
3. Elements with properties of both metals and non-metals are called metalloids.
4. Metals are good conductor of heat and electricity.
5. Metals are hard, malleable, lustrous and ductile.
6. Metals have high density and high melting points.
7. Non-metals are poor conductor of heat and electricity except graphite.
8. Metals are used for construction work, to make coin and jewerly.
9. Carbon is a non-metal and found in the form of coal or charcoal.
10. Carbon forms covalent bond because it has 4 electrons in its outermost orbit

and shares the electron of other elements.

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PRO J ECTWORK

Collect some substances in your surrounding. Identify what are metals and what
are non metals.

Exercise

1. Fill in the blanks.
a. The mixture of HCl and HNO3 is called……………..
b. …………….. is a coinage metal.
c. Silicon is an examples of …………………
d. ………… is source of carbon.
e. Gold has density……………& is the heaviest metal.

2. Write ‘True’ or ‘False’ for the following statements.
a. There is no specific ore of gold.
b. Germanium is an example of metalloids.
c. Iron is an alloy.
d. Silver is a useful to make ornaments.
e. Copper is not used to make coins.

3. Write short notes on.
a. Alloys b. Metalloids c. Coinage metal.

4. Answer the following questions.
a. What are metals and non-metals? Give examples.
b. Distinguish between metals and non-metals.
c. What are metalloids? Give examples.
d. Write any 3 properties of metalloids.
e. Define alloys with examples.
f. Write density of Cu, Al, Fe, Ag and Au.
g. Write 2/2 uses of Cu, Fe, Al and Ag.
h. Carbon forms covalent compound, explain.
i. Show electronic configuration of Fe, Al and Cu.
j. Write the ores of Fe, Al, Au and Cu.

Blooming Science & Environment Book 8 167

Glossary

Metal : hard, shining material which conduct electricity and produces deep
sound

Non-metal : dull, brittle material which is bad conductor

Metalloid : the substance which shows the properties of both metal and non-
metal

Malleable : property to change into thin plates

Ductile : property to change into thin wires.

Sonorous : giving deep sound

Lusture : quality of being bright/shining property

Conduct : to carry from one place to another

168 Blooming Science & Environment Book 8

Chapter Acid, Base and Salt

14

Learning Outcome Estimated Periods: 4+2

On the completion of this unit, the students will be able to:
 define acid, base and salt.
 tell properties and uses of acid, base and salt.
 describe indicator and use indicators to separate acid, base and salt.
 make litmus by using petals of flowers.
 describe pH scale in brief.

Compounds can broadly be classified in three main types namely acids, bases and
salts. This classification is based primarily upon the fact that each class has its own
characteristic properties.

Acids

An acid is a substance which dissociates in water to give positively charged hydrogen
(H+). H+ is called hydrogen ion.

For example, hydrogen chloride acid dissociates in water to give hydrogen ions and

chloride ions:

HCl water H+ + Cl-

The dissociation of acetic acid in aqueous solution is represented as:

CH3COOH water H+ + CH3COO-

Acetic acid

Some acids are commonly used in laboratory. They are also called inorganic acids.

S. No. Name Formula
HCl
1. Hydrochloric acid

2. Sulphuric acid H2SO4
3. Nitric acid HNO3
4. Phosphoric acid H3PO4

Blooming Science & Environment Book 8 169

Some acids give more H+ ions in aqueous solution because they ionize completely.
Such acids are called strong acids. For example, Hydrochloric acid, nitric acid and
sulphuric acid, etc. Their sources are usually minerlas and are also called inorganic
acids.
Some acids give less ions in aqueous soluition because they partially ionize. Such
acids are called weak acids. For example, acetic acid (CH3COOH), Carbonic acid
(H2CO3) formic acid (HCOOH) etc.
Those acids which are obtained from living sources are called organic acids. e.g.
acetic acid, formic acid etc.

Acids in Nature

Generally acid denotes a substance which tastes sour but in Chemistry, its meaning
is not limited up to this concept only. Acids are sour in taste. Most substances that
contain acid taste sour due to the presence of acid.

Many fruits like lemons, limes, grape fruits and orange contain citric acid. This is
what gives them a sour taste. Such fruits are also called citrus fruits. Unripe fruits
like green apples, plums and currants contain malic acid. The pickle gets its sourness
from vinegar or acetic acid. Sour milk contains lactic acid. Tartaric acid is present in
big lime (Bhogate).

It is not only in plants that acids are found. Insect-stings are often irritating because
of the acid injected into the wound. Ants use an acid called formic acid. Bee-stings
are also acidic.

In the human body, hydrochloric acid is made by the cells in the stomach. It helps in
the digestion of food. Vitamin C containing fruits have ascorbic acid.

There are some acids which are not sour. Acids like boric acid, stearic acid, are not
sour. In this unit we will study the properties of some common acids like hydrochloric
acid, sulphuric acid and nitric acid which are used in laboratory. Some organic acids
are listed below:

Acids Sources
1. Citric acid Lemon, tomatoes
2. Acetic acid Vinegar
3. Carbonic acid Soda water
4. Hydrochloric acid (weak) Stomach
5. Tartaric acid Fruits
6. Ascorbic acid Citrus fruits
7. Formic acid Ants (produced during ant’s bite)

170 Blooming Science & Environment Book 8

General Properties
Physical Properties
1. They all contain hydrogen.
2. They possess sour taste.
3. Many acids are corrosive.
4. They turn blue litmus red.
5. They turn methyl orange pink and phenolphthalein colourless.

Chemical Properties

1. Dilute acids react with some metals like zinc, magnesium etc. to form salt and
release hydrogen gas. The metals replace the hydrogen of acids to form a salt.

Mg + 2HCl → MgCl2 + H2

Hydrochloric acid Magnesium chloride

Zn + H2SO4 → ZNSO4 + H2

Sulphuric acid Zinc sulphate

2. Dilute acids decompose bicarbonate and carbonates and liberate carbon

dioxide.

NaHCO3 + HCl → NaCl + H2O + CO2

Sodium bicarbonate Hydrochloric acid

CaCO3 + 2HCl → CaCl2 + H2O + CO2

Calcium Hydrochloric Calcium

carbonate acid chloride

3. They neutralizes alkalis forming salt and water.

NaOH + HCl → NaCl + H2O
(water)
(alkali) (acid) (salt)

4. They react with metallic oxides to give salt and water.

CaO + 2HCl → CaCl2 + H2O
Calcium Water
Calcium Hydrochloric

oxide acid chloride

CuO + H2SO4 → CuSO4 + H2O

Copper Sulphuric Copper Water

oxide acid sulphate

Na2O + 2HNO3 → 2NaNO3 + H2O

Sodium Nitric Sodium Water

oxide acid nitrate

5. They dissolve in water to produce hydrogen ions (H+).

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Uses of Acids

Acids are widely used in industry. Tannic acid is used to tan leather. Sulphuric
acid, produced on a large scale, is used in the manufacture of ammonium sulphate,
an important fertilizer. Nitric and hydrochloric acids also use in many chemical
industries. Soda water consists of a large amount of carbon dioxide dissolved under
pressure in water. In other words, it is a very weak solution of carbonic acid. Baking
powder is usually made up of sodium bicarbonate (commonly called baking soda)
mixed with tartaric acid.

Bases

A base is defined as any substance which releases hydroxyl ions (OH-) when dissolved
in water. Sodium hydroxide and ammonia are bases because they give hydroxyl ions
in water.

NaOH water Na+ + OH-

Sodium hydroxide

NH3 + H2O → NH4+ + OH-
Ammonia
(Ammonium ion)

Bases which are soluble in water are called alkalis. Some bases are not soluble in
water. They are not alkalis. Thus, all alkalis are bases but all bases are not alkalis.
Sodium hydroxide is called caustic soda and potassium hydroxide is called caustic
potash.

Some bases are given below: Formula

Bases NaOH
1. Sodium hydroxide
2. Potassium hydroxide KOH
3. Aluminium hydroxide
4. Ammonium hydroxide Al(OH)3
5. Sodium oxide NH4OH
6. Potassium oxide Na2O
7. Magnesium oxide K2O
MgO

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