Chemistry - Kopykitab

Chemistry

Part I

Textbook for Class XI

2019-20

2 CHEMISTRY

ISBN 81-7450-494-X (Part I) 81-7450-535-0 (Part II)

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CoverShweta Rao

IllustrationsNidhi Wadhwa

Anil Nayal

First EditionMarch 2006 Phalguna 1927

ReprintedOctober 2006 Kartika 1928

November 2007 Kartika 1929

January 2009 Magha 1930

December 2009 Pausa 1931

November 2010 Kartika 1932

January 2012 Pausha 1933

November 2012 Kartika 1934

November 2013 Kartika 1935

December 2014 Pausa 1936

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3ANSWERS

FOREWORD

The National Curriculum Framework (NCF), 2005 recommends that children’s life atschool must be linked to their life outside the school. This principle marks a departurefrom the legacy of bookish learning which continues to shape our system and causes agap between the school, home and community. The syllabi and textbooks developed onthe basis of NCF signify an attempt to implement this basic idea. They also attempt todiscourage rote learning and the maintenance of sharp boundaries between differentsubject areas. We hope these measures will take us significantly further in the direction ofa child-centred system of education outlined in the National Policy on Education (1986).

The success of this effort depends on the steps that school principals and teacherswill take to encourage children to reflect on their own learning and to pursueimaginative activities and questions. We must recognise that, given space, time andfreedom, children generate new knowledge by engaging with the information passedon to them by adults. Treating the prescribed textbook as the sole basis of examinationis one of the key reasons why other resources and sites of learning are ignored.Inculcating creativity and initiative is possible if we perceive and treat children asparticipants in learning, not as receivers of a fixed body of knowledge.

These aims imply considerable change in school routines and mode of functioning.Flexibility in the daily time-table is as necessary as rigour in implementing the annualcalender so that the required number of teaching days are actually devoted to teaching.The methods used for teaching and evaluation will also determine how effective thistextbook proves for making children’s life at school a happy experience, rather than asource of stress or boredom. Syllabus designers have tried to address the problem ofcurricular burden by restructuring and reorienting knowledge at different stageswith greater consideration for child psychology and the time available for teaching.The textbook attempts to enhance this endeavour by giving higher priority and spaceto opportunities for contemplation and wondering, discussion in small groups, andactivities requiring hands-on experience.

The National Council of Educational Research and Training (NCERT) appreciatesthe hard work done by the textbook development committee responsible for this book.We wish to thank the Chairperson of the advisory group in science and mathematics,Professor J.V. Narlikar and the Chief Advisor for this book, Professor B. L. Khandelwalfor guiding the work of this committee. Several teachers contributed to the developmentof this textbook; we are grateful to their principals for making this possible. We areindebted to the institutions and organisations which have generously permitted us todraw upon their resources, material and personnel. As an organisation committed tosystemic reform and continuous improvement in the quality of its products, NCERTwelcomes comments and suggestions which will enable us to undertake furtherrevision and refinement.

Director

New Delhi National Council of Educational20 December 2005 Research and Training

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4 CHEMISTRY

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5ANSWERS

TEXTBOOK DEVELOPMENT COMMITTEE

CHAIRPERSON, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS

J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee, InterUniversity Centre for Astronomy and Astrophysics (IUCCA), Ganeshbhind,Pune University, Pune

CHIEF ADVISOR

B.L. Khandelwal, Professor (Retd.), Emeritus Scientist, CSIR; Emeritus Fellow, AICTEand formerly Chairman, Department of Chemistry, Indian Institute of Technology,

New Delhi

MEMBERS

A. S. Brar, Professor, Indian Institute of Technology, Delhi

Anjni Koul, Lecturer, DESM, NCERT, New Delhi

H.O. Gupta, Professor, DESM, NCERT, New Delhi

I.P. Aggarwal, Professor, Regional Institute of Education, Bhopal

Jaishree Sharma, Professor, DESM, NCERT, New Delhi

M. Chandra, Professor, DESM, NCERT, New Delhi

Poonam Sawhney, PGT (Chemistry), Kendriya Vidyalaya, Vikas Puri, New Delhi

R.K. Parashar, Lecturer, DESM, NCERT, New Delhi

S.K. Dogra, Professor, Dr. B.R. Ambedkar Centre for Biomedical Research, University ofDelhi, Delhi

S.K. Gupta, Reader, School of Studies in Chemistry, Jiwaji University, Gwalior

Sadhna Bhargava, PGT (Chemistry), Sardar Patel Vidyalaya, Lodhi Estate, New Delhi

Shubha Keshwan, Headmistress, Demonstration School, Regional Institute of Education,

Mysuru

Sukhvir Singh, Reader, DESM, NCERT, New Delhi

Sunita Malhotra, Professor, School of Sciences, IGNOU, Maidan Garhi, New Delhi

V.K. Verma, Professor (Retd.), Institute of Technology, Banaras Hindu University, Varanasi

V.P. Gupta, Reader, Regional Institute of Education, Bhopal

MEMBER-COORDINATOR

Alka Mehrotra, Reader, DESM, NCERT, New Delhi

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6 CHEMISTRY

ACKNOWLEDGEMENTS

The National Council of Educational Research and Training acknowledges the valuablecontributions of the individuals and organisations involved in the development ofChemistry textbook for Class XI. It also acknowledges that some useful material fromthe reprint editions (2005) of Chemistry textbooks has been utilised in the developmentof the present textbook.

The following academics contributed effectively in editing, reviewing, refining andfinalisation of the manuscript of this book: G.T. Bhandage, Professor, RIE, Mysuru;N. Ram, Professor, IIT, New Delhi; Sanjeev Kumar, Associate Professor, School ofScience, IGNOU, Maidan Garhi, New Delhi; Shampa Bhattacharya, Associate

Professor, Hans Raj College, Delhi; Vijay Sarda, Associate Professor (Retd.), ZakirHusain College, New Delhi; K.K. Arora, Associate Professor, Zakir Husain College,New Delhi; Shashi Saxena, Associate Professor, Hans Raj College, Delhi; AnuradhaSen, Apeejay School, Sheikh Sarai, New Delhi; C. Shrinivas, PGT, Kendriya Vidyalaya,Pushp Vihar, New Delhi; D.L. Bharti, PGT, Ramjas School, Sector IV, R.K. Puram, NewDelhi; Ila Sharma, PGT, Delhi Public School, Dwarka, Sector-B, New Delhi; Raj LakshmiKarthikeyan, Head (Science), Mother’s International School, Sri Aurobindo Marg, NewDelhi; Sushma Kiran Setia, Principal, Sarvodaya Kanya Vidyalaya, Hari Nagar (CT),New Delhi; Nidhi Chaudray, PGT, CRPF Public School, Rohini, Delhi; and Veena Suri,PGT, Bluebells School, Kailash Colony, New Delhi. We are thankful to them.

We express our gratitude to R.S. Sindhu, Professor (Retd.), DESM, NCERT, NewDelhi, for editing and refining the content of the textbook right from the initial stage.

We are also grateful to Ruchi Verma, Associate Professor, DESM, NCERT, NewDelhi; Pramila Tanwar, Assistant Professor, DESM, NCERT, New Delhi; R.B. Pareek,Associate Professor, RIE, Ajmer; and A.K. Arya, Associate Professor, RIE, Ajmer, forrefining the content of the textbook.

Special thanks are due to M. Chandra, Professor and Head (Retd.), DESM, NCERTfor her support.

The Council also gratefully acknowledges the contributions of Surendra Kumar,Narender Verma and Ramesh Kumar, DTP Operators; Subhash Saluja, RamendraKumar Sharma and Abhimanyu Mohanty, Proofreaders; Bhavna Saxena, Copy

Editor; and Deepak Kapoor, In-charge, Computer Station, in shaping this book. Thecontributions of the Publication Department, NCERT, New Delhi, in bringing out thisbook are also duly acknowledged.

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7ANSWERS

CONTENTS

Foreword iii

Unit 1 Some Basic Concepts of Chemistry 1

1.1 Importance of Chemistry 4

1.2 Nature of Matter 4

1.3 Properties of Matter and their Measurement 6

1.4 Uncertainty in Measurement 10

1.5 Laws of Chemical Combinations 14

1.6 Dalton’s Atomic Theory 16

1.7 Atomic and Molecular Masses 16

1.8 Mole Concept and Molar Masses 18

1.9 Percentage Composition 18

1.10 Stoichiometry and Stoichiometric Calculations 20

Unit 2 Structure of Atom 29

2.1 Discovery of Sub-atomic Particles 30

2.2 Atomic Models 32

2.3 Developments Leading to the Bohr’s Model of Atom 37

2.4 Bohr’s Model for Hydrogen Atom 46

2.5 Towards Quantum Mechanical Model of the Atom 49

2.6 Quantum Mechanical Model of Atom 53

Unit 3 Classification of Elements and Periodicity in Properties 74

3.1 Why do we Need to Classify Elements ? 74

3.2 Genesis of Periodic Classification 75

3.3 Modern Periodic Law and the present form of the Periodic Table 79

3.4 Nomenclature of Elements with Atomic Numbers > 100 79

3.5 Electronic Configurations of Elements and the Periodic Table 82

3.6 Electronic Configurations and Types of Elements: 83

s-, p-, d-, f- Blocks

3.7 Periodic Trends in Properties of Elements 86

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Unit 4 Chemical Bonding and Molecular Structure 100

4.1 Kössel-Lewis Approach to Chemical Bonding 101

4.2 Ionic or Electrovalent Bond 106

4.3 Bond Parameters 107

4.4 The Valence Shell Electron Pair Repulsion (VSEPR) Theory 112

4.5 Valence Bond Theory 117

4.6 Hybridisation 120

4.7 Molecular Orbital Theory 125

4.8 Bonding in Some Homonuclear Diatomic Molecules 129

4.9 Hydrogen Bonding 131

Unit 5 States of Matter 136

5.1 Intermolecular Forces 137

5.2 Thermal Energy 139

5.3 Intermolecular Forces vs Thermal Interactions 139

5.4 The Gaseous State 139

5.5 The Gas Laws 140

5.6 Ideal Gas Equation 145

5.7 Kinetic Energy and Molecular Speeds 147

5.8 Kinetic Molecular Theory of Gases 149

5.9 Behaviour of Real Gases: Deviation from Ideal Gas Behaviour 150

5.10 Liquefaction of Gases 152

5.11 Liquid State 154

Unit 6 Thermodynamics 160

6.1 Thermodynamic Terms 161

6.2 Applications 164

6.3 Measurement of ∆U and ∆H: Calorimetry 169

6.4 Enthalpy Change, ∆rH of a Reaction – Reaction Enthalpy 171

6.5 Enthalpies for Different Types of Reactions 176

6.6 Spontaneity 181

6.7 Gibbs Energy Change and Equilibrium 186

(viii )

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Unit 7 Equilibrium 192

7.1 Equilibrium in Physical Processes 193

7.2 Equilibrium in Chemical Processes – Dynamic Equilibrium 196

7.3 Law of Chemical Equilibrium and Equilibrium Constant 198

7.4 Homogeneous Equilibria 201

7.5 Heterogeneous Equilibria 203

7.6 Applications of Equilibrium Constants 205

7.7 Relationship between Equilibrium Constant K, 208

Reaction Quotient Q and Gibbs Energy G

7.8 Factors Affecting Equilibria 208

7.9 Ionic Equilibrium in Solution 212

7.10 Acids, Bases and Salts 213

7.11 Ionization of Acids and Bases 216

7.12 Buffer Solutions 226

7.13 Solubility Equilibria of Sparingly Soluble Salts 228

Appendices 239

Answer to some Selected Questions 253

Index 259

( i x)

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UNIT 1

SOME BASIC CONCEPTS OF CHEMISTRY

Chemistry is the science of molecules and theirtransformations. It is the science not so much of the onehundred elements but of the infinite variety of molecules thatmay be built from them.

Roald Hoffmann

Science can be viewed as a continuing human effort tosystematise knowledge for describing and understandingnature. You have learnt in your previous classes that we comeacross diverse substances present in nature and changes inthem in daily life. Curd formation from milk, formation ofvinegar from sugarcane juice on keeping for prolonged timeand rusting of iron are some of the examples of changes whichwe come across many times. For the sake of convenience,science is sub-divided into various disciplines: chemistry,physics, biology, geology, etc. The branch of science thatstudies the preparation, properties, structure and reactionsof material substances is called chemistry.

DEVELOPMENT OF CHEMISTRY

Chemistry, as we understand it today, is not a very olddiscipline. Chemistry was not studied for its own sake, ratherit came up as a result of search for two interesting things:

i. Philosopher’s stone (Paras) which would convert all baser metals e.g., iron and copper into gold.ii.‘Elexir of life’ which would grant immortality.

People in ancient India, already had the knowledge of manyscientific phenomenon much before the advent of modernscience. They applied that knowledge in various walks oflife. Chemistry developed mainly in the form of Alchemyand Iatrochemistry during 1300-1600 CE. Modernchemistry took shape in the 18th century Europe, after afew centuries of alchemical traditions which wereintroduced in Europe by the Arabs.

After studying this unit, you will beable to

••••• appreciate the contribution of

India in the development ofchemistry understand the role ofchemistry in different spheres oflife;

••••• explain the characteristics ofthree states of matter;

••••• classify different substances into

elements, compounds andmixtures;

••••• use scientific notations anddetermine significant figures;

••••• differentiate between precision and

accuracy;

••••• define SI base units and convert

physical quantities from onesystem of units to another;

••••• explain various laws of chemical

combination;

••••• appreciate significance of atomic

mass, average atomic mass,molecular mass and formulamass;

••••• describe the terms – mole andmolar mass;

••••• calculate the mass per cent of

component elements constitutinga compound;

••••• determine empirical formula andmolecular formula for a compoundfrom the given experimental data;and

••••• perform the stoichiometric

calculations.

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Other cultures – especially the Chinese andthe Indian – had their own alchemical traditions.These included much knowledge of chemicalprocesses and techniques.

In ancient India, chemistry was calledRasayan Shastra, Rastantra, Ras Kriya orRasvidya. It included metallurgy, medicine,manufacture of cosmetics, glass, dyes, etc.Systematic excavations at Mohenjodaro inSindh and Harappa in Punjab prove that thestory of development of chemistry in India isvery old. Archaeological findings show thatbaked bricks were used in construction work.It shows the mass production of pottery, whichcan be regarded as the earliest chemical process,in which materials were mixed, moulded andsubjected to heat by using fire to achievedesirable qualities. Remains of glazed potteryhave been found in Mohenjodaro. Gypsumcement has been used in the construction work.It contains lime, sand and traces of CaCO

3.

Harappans made faience, a sort of glass whichwas used in ornaments. They melted and forgeda variety of objects from metals, such as lead,silver, gold and copper. They improved thehardness of copper for making artefacts byusing tin and arsenic. A number of glass objectswere found in Maski in South India (1000–900BCE), and Hastinapur and Taxila in NorthIndia (1000–200 BCE). Glass and glazes werecoloured by addition of colouring agents like

metal oxides.

Copper metallurgy in India dates back tothe beginning of chalcolithic cultures in thesubcontinent. There are much archeologicalevidences to support the view that technologiesfor extraction of copper and iron were developedindigenously.

According to Rigveda, tanning of leatherand dying of cotton were practised during1000–400 BCE. The golden gloss of the blackpolished ware of northen India could not bereplicated and is still a chemical mystery. Thesewares indicate the mastery with which kilntemperatures could be controlled. Kautilya’sArthashastra describes the production of saltfrom sea.

A vast number of statements and materialdescribed in the ancient Vedic literature can

be shown to agree with modern scientific

findings. Copper utensils, iron, gold, silver

ornaments and terracotta discs and painted

grey pottery have been found in many

archaeological sites in north India. Sushruta

Samhita explains the importance of Alkalies.

The Charaka Samhita mentions ancient

indians who knew how to prepare sulphuric

acid, nitric acid and oxides of copper, tin and

zinc; the sulphates of copper, zinc and iron and

the carbonates of lead and iron.

Rasopanishada describes the preparation

of gunpowder mixture. Tamil texts also

describe the preparation of fireworks using

sulphur, charcoal, saltpetre (i.e., potassium

nitrate), mercury, camphor, etc.

Nagarjuna was a great Indian scientist. He

was a reputed chemist, an alchemist and a

metallurgist. His work Rasratnakar deals with

the formulation of mercury compounds. He has

also discussed methods for the extraction of

metals, like gold, silver, tin and copper. A book,

Rsarnavam, appeared around 800 CE. It

discusses the uses of various furnaces, ovens

and crucibles for different purposes. It

describes methods by which metals could be

identified by flame colour.

Chakrapani discovered mercury sulphide.

The credit for inventing soap also goes to him.

He used mustard oil and some alkalies as

ingredients for making soap. Indians began

making soaps in the 18th century CE. Oil of

Eranda and seeds of Mahua plant and calcium

carbonate were used for making soap.

The paintings found on the walls of Ajanta

and Ellora, which look fresh even after ages,

testify to a high level of science achieved in

ancient India. Varähmihir’s Brihat Samhita is

a sort of encyclopaedia, which was composed

in the sixth century CE. It informs about the

preparation of glutinous material to be applied

on walls and roofs of houses and temples. It

was prepared entirely from extracts of various

plants, fruits, seeds and barks, which were

concentrated by boiling, and then, treated with

various resins. It will be interesting to test such

materials scientifically and assess them for use.

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3SOME BASIC CONCEPTS OF CHEMISTRY

A number of classical texts, likeAtharvaveda (1000 BCE) mention some dyestuff, the material used were turmeric, madder,sunflower, orpiment, cochineal and lac. Someother substances having tinting property werekamplcica, pattanga and jatuka.

Varähmihir’s Brihat Samhita givesreferences to perfumes and cosmetics. Recipesfor hair dying were made from plants, likeindigo and minerals like iron power, black ironor steel and acidic extracts of sour rice gruel.Gandhayukli describes recipes for makingscents, mouth perfumes, bath powders,incense and talcum power.

Paper was known to India in the17th century as account of Chinese travellerI-tsing describes. Excavations at Taxila indicatethat ink was used in India from the fourthcentury. Colours of ink were made from chalk,red lead and minimum.

It seems that the process of fermentationwas well-known to Indians. Vedas andKautilya’s Arthashastra mention about manytypes of liquors. Charaka Samhita alsomentions ingredients, such as barks of plants,stem, flowers, leaves, woods, cereals, fruits andsugarcane for making Asavas.

The concept that matter is ultimately madeof indivisible building blocks, appeared inIndia a few centuries BCE as a part ofphilosophical speculations. Acharya Kanda,born in 600 BCE, originally known by thename Kashyap, was the first proponent of the‘atomic theory’. He formulated the theory ofvery small indivisible particles, which henamed ‘Paramãnu’ (comparable to atoms). Heauthored the text Vaiseshika Sutras.According to him, all substances areaggregated form of smaller units called atoms(Paramãnu), which are eternal, indestructible,spherical, suprasensible and in motion in theoriginal state. He explained that this individualentity cannot be sensed through any humanorgan. Kanda added that there are varieties ofatoms that are as different as the differentclasses of substances. He said these(Paramãnu) could form pairs or triplets, amongother combinations and unseen forces cause

interaction between them. He conceptualisedthis theory around 2500 years before JohnDalton (1766-1844).

Charaka Samhita is the oldest Ayurvedicepic of India. It describes the treatment ofdiseases. The concept of reduction of particlesize of metals is clearly discussed in Charaka

Samhita. Extreme reduction of particle size istermed as nanotechnology. Charaka Samhita

describes the use of bhasma of metals in thetreatment of ailments. Now-a-days, it has beenproved that bhasmas have nanoparticles ofmetals.

After the decline of alchemy, Iatrochemistryreached a steady state, but it too declined dueto the introduction and practise of westernmedicinal system in the 20th century. Duringthis period of stagnation, pharmaceuticalindustry based on Ayurveda continued toexist, but it too declined gradually. It tookabout 100-150 years for Indians to learn andadopt new techniques. During this time, foreignproducts poured in. As a result, indigenoustraditional techniques gradually declined.Modern science appeared in Indian scene inthe later part of the nineteenth century. By themid-nineteenth century, European scientistsstarted coming to India and modern chemistrystarted growing.

From the above discussion, you have learnt

that chemistry deals with the composition,structure, properties and interection of matterand is of much use to human beings in daily

life. These aspects can be best described andunderstood in terms of basic constituents ofmatter that are atoms and molecules. That

is why, chemistry is also called the science ofatoms and molecules. Can we see, weigh andperceive these entities (atoms and molecules)?

Is it possible to count the number of atomsand molecules in a given mass of matter andhave a quantitative relationship between the

mass and the number of these particles? Wewill get the answer of some of these questionsin this Unit. We will further describe how

physical properties of matter can bequantitatively described using numerical

values with suitable units.

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4 CHEMISTRY

1.1 IMPORTANCE OF CHEMISTRY

Chemistry plays a central role in science andis often intertwined with other branches ofscience.

Principles of chemistry are applicable indiverse areas, such as weather patterns,functioning of brain and operation of acomputer, production in chemical industries,manufacturing fertilisers, alkalis, acids, salts,dyes, polymers, drugs, soaps, detergents,metals, alloys, etc., including new material.

Chemistry contributes in a big way to thenational economy. It also plays an importantrole in meeting human needs for food,healthcare products and other materialaimed at improving the quality of life. Thisis exemplified by the large-scale productionof a variety of fertilisers, improved variety ofpesticides and insecticides. Chemistryprovides methods for the isolation of life-saving drugs from natural sources andmakes possible synthesis of such drugs.Some of these drugs are cisplatin and taxol,which are effective in cancer therapy. Thedrug AZT (Azidothymidine) is used forhelping AIDS patients.

Chemistry contributes to a large extentin the development and growth of a nation.With a better understanding of chemicalprinciples it has now become possible todesign and synthesise new material havingspecific magnetic, electric and opticalproperties. This has lead to the productionof superconducting ceramics, conductingpolymers, optical fibres, etc. Chemistry hashelped in establishing industries whichmanufacture utility goods, like acids,alkalies, dyes, polymesr metals, etc. Theseindustries contribute in a big way to theeconomy of a nation and generateemployment.

In recent years, chemistry has helpedin dealing with some of the pressing aspectsof environmental degradation with a fairdegree of success. Safer alternatives toenvironmentally hazardous refrigerants, likeCFCs (chlorofluorocarbons), responsible forozone depletion in the stratosphere, have

been successfully synthesised. However,many big environmental problems continueto be matters of grave concern to thechemists. One such problem is themanagement of the Green House gases, likemethane, carbon dioxide, etc. Understandingof biochemical processes, use of enzymes forlarge-scale production of chemicals andsynthesis of new exotic material are some ofthe intellectual challenges for the futuregeneration of chemists. A developing country,like India, needs talented and creativechemists for accepting such challenges. Tobe a good chemist and to accept suchchallanges, one needs to understand thebasic concepts of chemistry, which begin withthe concept of matter. Let us start with thenature of matter.

1.2 NATURE OF MATTER

You are already familiar with the term matterfrom your earlier classes. Anything which hasmass and occupies space is called matter.Everything around us, for example, book, pen,pencil, water, air, all living beings, etc., arecomposed of matter. You know that they havemass and they occupy space. Let us recall thecharacteristics of the states of matter, whichyou learnt in your previous classes.

1.2.1 States of MatterYou are aware that matter can exist in threephysical states viz. solid, liquid and gas. Theconstituent particles of matter in these threestates can be represented as shown in Fig. 1.1.

Particles are held very close to each otherin solids in an orderly fashion and there is notmuch freedom of movement. In liquids, theparticles are close to each other but they canmove around. However, in gases, the particlesare far apart as compared to those present insolid or liquid states and their movement iseasy and fast. Because of such arrangementof particles, different states of matter exhibitthe following characteristics:(i) Solids have definite volume and definite

shape.

(ii) Liquids have definite volume but do not

have definite shape. They take the shapeof the container in which they are placed.

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NCERT Chemistry Part - I Textbook For Class - XI(Latest Edition)

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