NCERT Chemistry Part 1. PDF

Chemistry Part I Textbook for Class XI Rationalised 2023-24 Prelims.indd 1 10/11/2022 4:01:56 PM  2...

Chemistry Part I Textbook for Class XI Rationalised 2023-24 Prelims.indd 1 10/11/2022 4:01:56 PM  2 CHEMISTRY 11082 – Chemistry Part I ISBN 81-7450-494-X (Part I) Textbook for Class XI 81-7450-535-0 (Part II) First Edition ALL RIGHTS RESERVED  No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, March 2006 Phalguna 1927 photocopying, recording or otherwise without the prior permission of the publisher. Reprinted  This book is sold subject to the condition that it shall not, by way of trade, be lent, October 2006 Kartika 1928 re-sold, hired out or otherwise disposed of without the publisher’s consent, in any form of binding or cover other than that in which it is published. November 2007 Kartika 1929  The correct price of this publication is the price printed on this page. Any revised January 2009 Magha 1930 price indicated by a rubber stamp or by a sticker or by any other means is December 2009 Pausa 1931 incorrect and should be unacceptable. November 2010 Kartika 1932 January 2012 Pausha 1933 OFFICES OF THE PUBLICATION November 2012 Kartika 1934 DIVISION, NCERT November 2013 Kartika 1935 NCERT Campus December 2014 Pausa 1936 Sri Aurobindo Marg New Delhi 110 016 Phone : 011-26562708 May 2016 Vaishakha 1938 January 2018 Magha 1939 108, 100 Feet Road December 2018 Agrahayana 1940 Hosdakere Halli Extension Banashankari III Stage October 2019 Ashwina 1941 Bengaluru 560 085 Phone : 080-26725740 July 2021 Asadha 1943 August 2022 Bhadrapada 1944 Navjivan Trust Building P.O.Navjivan Revised Edition Ahmedabad 380 014 Phone : 079-27541446 October 2022 Ashwina 1944 CWC Campus Opp. Dhankal Bus Stop PD 320T RSP Panihati Kolkata 700 114 Phone : 033-25530454 © National Council of Educational CWC Complex Research and Training, 2006, 2022 Maligaon Guwahati 781 021 Phone : 0361-2674869 Publication Team Head, Publication : Anup Kumar Rajput Division Chief Production : Arun Chitkara ` 180.00 Officer Chief Business : Vipin Dewan Manager Chief Editor (In charge) : Bijnan Sutar Editor : Benoy Banerjee Printed on 80 GSM paper with NCERT Production Assistant : Om Prakash watermark Cover Published at the Publication Division Shweta Rao by the Secretary, National Council of Educational Research and Training, Illustrations Sri Aurobindo Marg, New Delhi 110 016 Nidhi Wadhwa and printed at Educational Stores, S-5, Anil Nayal Bulandshahar Road, Industrial Area Site-I (Near RTO Office) Ghaziabad (U.P.) Rationalised 2023-24 Prelims.indd 2 12/1/2022 16:12:33  answerS 3 Foreword The National Curriculum Framework (NCF), 2005 recommends that children’s life at school must be linked to their life outside the school. This principle marks a departure from the legacy of bookish learning which continues to shape our system and causes a gap between the school, home and community. The syllabi and textbooks developed on the basis of NCF signify an attempt to implement this basic idea. They also attempt to discourage rote learning and the maintenance of sharp boundaries between different subject areas. We hope these measures will take us significantly further in the direction of a 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 teachers will take to encourage children to reflect on their own learning and to pursue imaginative activities and questions. We must recognise that, given space, time and freedom, children generate new knowledge by engaging with the information passed on to them by adults. Treating the prescribed textbook as the sole basis of examination is 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 as participants 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 annual calender 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 this textbook proves for making children’s life at school a happy experience, rather than a source of stress or boredom. Syllabus designers have tried to address the problem of curricular burden by restructuring and reorienting knowledge at different stages with greater consideration for child psychology and the time available for teaching. The textbook attempts to enhance this endeavour by giving higher priority and space to opportunities for contemplation and wondering, discussion in small groups, and activities requiring hands-on experience. The National Council of Educational Research and Training (NCERT) appreciates the 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. Khandelwal for guiding the work of this committee. Several teachers contributed to the development of this textbook; we are grateful to their principals for making this possible. We are indebted to the institutions and organisations which have generously permitted us to draw upon their resources, material and personnel. As an organisation committed to systemic reform and continuous improvement in the quality of its products, NCERT welcomes comments and suggestions which will enable us to undertake further revision and refinement. Director New Delhi National Council of Educational 20 December 2005 Research and Training Rationalised 2023-24 Prelims.indd 3 10/11/2022 4:01:56 PM  4 chemistry Rationalised 2023-24 Prelims.indd 4 10/11/2022 4:01:56 PM  answerS 5 Rationalisation of Content in the Textbooks In view of the COVID-19 pandemic, it is imperative to reduce content load on students. The National Education Policy 2020, also emphasises reducing the content load and providing opportunities for experiential learning with creative mindset. In this background, the NCERT has undertaken the exercise to rationalise the textbooks across all classes. Learning Outcomes already developed by the NCERT across classes have been taken into consideration in this exercise. Contents of the textbooks have been rationalised in view of the following: Overlapping with similar content included in other subject areas in the same class Similar content included in the lower or higher class in the same subject Difficulty level Content, which is easily accessible to students without much interventions from teachers and can be learned by children through self-learning or peer-learning Content, which is irrelevant in the present context This present edition, is a reformatted version after carrying out the changes given above. Rationalised 2023-24 Prelims.indd 5 10/11/2022 4:01:56 PM  6 chemistry Rationalised 2023-24 Prelims.indd 6 10/11/2022 4:01:56 PM  answerS 7 Textbook Development Committee Chairperson, Advisory Group for Textbooks in Science and Mathematics J.V. Narlikar, Emeritus Professor, Chairman, Advisory Committee, Inter University Centre for Astronomy and Astrophysics (IUCCA), Ganeshbhind, Pune University, Pune Chief Advisor B.L. Khandelwal, Professor (Retd.), Emeritus Scientist, CSIR; Emeritus Fellow, AICTE and 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 of Delhi, 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 Rationalised 2023-24 Prelims.indd 7 11/2/2022 4:35:40 PM  8 chemistry Acknowledgements The National Council of Educational Research and Training acknowledges the valuable contributions of the individuals and organisations involved in the development of Chemistry textbook for Class XI. It also acknowledges that some useful material from the reprint editions (2005) of Chemistry textbooks has been utilised in the development of the present textbook. The following academics contributed effectively in editing, reviewing, refining and finalisation of the manuscript of this book: G.T. Bhandage, Professor, RIE, Mysuru; N. Ram, Professor, IIT, New Delhi; Sanjeev Kumar, Associate Professor, School of Science, IGNOU, Maidan Garhi, New Delhi; Shampa Bhattacharya, Associate Professor, Hans Raj College, Delhi; Vijay Sarda, Associate Professor (Retd.), Zakir Husain College, New Delhi; K.K. Arora, Associate Professor, Zakir Husain College, New Delhi; Shashi Saxena, Associate Professor, Hans Raj College, Delhi; Anuradha Sen, 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, New Delhi; Ila Sharma, PGT, Delhi Public School, Dwarka, Sector-B, New Delhi; Raj Lakshmi Karthikeyan, Head (Science), Mother’s International School, Sri Aurobindo Marg, New Delhi; 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, New Delhi, 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, New Delhi; Pramila Tanwar, Associate Professor, DESM, NCERT, New Delhi; R.B. Pareek, Associate Professor, RIE, Ajmer; and A.K. Arya, Associate Professor, RIE, Ajmer, for refining the content of the textbook. Special thanks are due to M. Chandra, Professor and Head (Retd.), DESM, NCERT for her support. The Council also gratefully acknowledges the contributions of Surendra Kumar, Narender Verma and Ramesh Kumar, DTP Operators; Subhash Saluja, Ramendra Kumar Sharma and Abhimanyu Mohanty, Proofreaders; Bhavna Saxena, Copy Editor; and Deepak Kapoor, In-charge, Computer Station, in shaping this book. The contributions of the Publication Department, NCERT, New Delhi, in bringing out this book are also duly acknowledged. Rationalised 2023-24 Prelims.indd 8 11/2/2022 4:43:38 PM  answerS 9 Contents Foreword iii Rationalisation of Content in the Textbooks v 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 78 3.4 Nomenclature of Elements with Atomic Numbers > 100 78 3.5 Electronic Configurations of Elements and the Periodic Table 81 Rationalised 2023-24 Prelims.indd 9 10/11/2022 4:01:56 PM  10 (x) chemistry 3.6 Electronic Configurations and Types of Elements: 82 s-, p-, d-, f- Blocks 3.7 Periodic Trends in Properties of Elements 85 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 Thermodynamics 136 5.1 Thermodynamic Terms 137 5.2 Applications 140 5.3 Measurement of ∆U and ∆H: Calorimetry 145 5.4 Enthalpy Change, ∆rH of a Reaction – Reaction Enthalpy 146 5.5 Enthalpies for Different Types of Reactions 152 5.6 Spontaneity 157 5.7 Gibbs Energy Change and Equilibrium 162 Unit 6 Equilibrium 168 6.1 Equilibrium in Physical Processes 169 6.2 Equilibrium in Chemical Processes – Dynamic Equilibrium 172 6.3 Law of Chemical Equilibrium and Equilibrium Constant 174 6.4 Homogeneous Equilibria 177 6.5 Heterogeneous Equilibria 179 6.6 Applications of Equilibrium Constants 181 6.7 Relationship between Equilibrium Constant K, 184 Reaction Quotient Q and Gibbs Energy G Rationalised 2023-24 Prelims.indd 10 10/11/2022 4:01:56 PM  answerS (xi ) 11 6.8 Factors Affecting Equilibria 184 6.9 Ionic Equilibrium in Solution 188 6.10 Acids, Bases and Salts 189 6.11 Ionization of Acids and Bases 192 6.12 Buffer Solutions 202 6.13 Solubility Equilibria of Sparingly Soluble Salts 204 Appendices 215 Answer to Some Selected Problems 229 Rationalised 2023-24 Prelims.indd 11 10/11/2022 4:01:56 PM  12 chemistry Rationalised 2023-24 Prelims.indd 12 10/11/2022 4:01:59 PM  Unit 1 Some Basic Concepts of Chemistry Chemistry is the science of molecules and their transformations. It is the science not so much of the one hundred elements but of the infinite variety of molecules After studying this unit, you will be that may be built from them. able to appreciate the contribution of India Roald Hoffmann in the development of chemistry understand the role of chemistry in different spheres of life; Science can be viewed as a continuing human effort to explain the characteristics of three systematise knowledge for describing and understanding states of matter; nature. You have learnt in your previous classes that we classify different substances come across diverse substances present in nature and into elements, compounds and changes in them in daily life. Curd formation from milk, mixtures; formation of vinegar from sugarcane juice on keeping use scientific notations and for prolonged time and rusting of iron are some of the determine significant figures; examples of changes which we come across many times. differentiate between precision and For the sake of convenience, science is sub-divided into accuracy; various disciplines: chemistry, physics, biology, geology, define SI base units and convert etc. The branch of science that studies the preparation, physical quantities from one system of units to another; properties, structure and reactions of material substances explain various laws of chemical is called chemistry. combination; Development of chemistry appreciate significance of atomic Chemistry, as we understand it today, is not a very old mass, average atomic mass, discipline. Chemistry was not studied for its own sake, rather molecular mass and formula mass; it came up as a result of search for two interesting things: describe the terms – mole and molar mass; i. Philosopher’s stone (Paras) which would convert all baser metals e.g., iron and copper into gold. calculate the mass per cent of component elements constituting ii. ‘Elexir of life’ which would grant immortality. a compound; People in ancient India, already had the knowledge of determine empirical formula and many scientific phenomenon much before the advent of molecular formula for a compound modern science. They applied that knowledge in various from the given experimental data; walks of life. Chemistry developed mainly in the form and of Alchemy and Iatrochemistry during 1300-1600 CE. perform the stoichiometric Modern chemistry took shape in the 18th century Europe, calculations. after a few centuries of alchemical traditions which were introduced in Europe by the Arabs. Rationalised 2023-24 Unit 1.indd 1 9/9/2022 4:27:29 PM  2 chemistry Other cultures – especially the Chinese be shown to agree with modern scientific and the Indian – had their own alchemical findings. Copper utensils, iron, gold, silver traditions. These included much knowledge of ornaments and terracotta discs and painted chemical processes and techniques. grey pottery have been found in many In ancient India, chemistry was called archaeological sites in north India. Sushruta Rasayan Shastra, Rastantra, Ras Kriya or Samhita explains the importance of Alkalies. Rasvidya. It included metallurgy, medicine, The Charaka Samhita mentions ancient manufacture of cosmetics, glass, dyes, etc. indians who knew how to prepare sulphuric Systematic excavations at Mohenjodaro in acid, nitric acid and oxides of copper, tin and Sindh and Harappa in Punjab prove that the zinc; the sulphates of copper, zinc and iron story of development of chemistry in India and the carbonates of lead and iron. is very old. Archaeological findings show that baked bricks were used in construction Rasopanishada describes the preparation work. It shows the mass production of of gunpowder mixture. Tamil texts also pottery, which can be regarded as the earliest describe the preparation of fireworks using chemical process, in which materials were sulphur, charcoal, saltpetre (i.e., potassium mixed, moulded and subjected to heat by nitrate), mercury, camphor, etc. using fire to achieve desirable qualities. Nagarjuna was a great Indian scientist. He Remains of glazed pottery have been found in was a reputed chemist, an alchemist and a Mohenjodaro. Gypsum cement has been used metallurgist. His work Rasratnakar deals with in the construction work. It contains lime, the formulation of mercury compounds. He sand and traces of CaCO3. Harappans made has also discussed methods for the extraction faience, a sort of glass which was used in of metals, like gold, silver, tin and copper. A ornaments. They melted and forged a variety book, Rsarnavam, appeared around 800 CE. of objects from metals, such as lead, silver, It discusses the uses of various furnaces, gold and copper. They improved the hardness ovens and crucibles for different purposes. It of copper for making artefacts by using tin describes methods by which metals could be and arsenic. A number of glass objects were found in Maski in South India (1000–900 identified by flame colour. BCE), and Hastinapur and Taxila in North Chakrapani discovered mercury sulphide. India (1000–200 BCE). Glass and glazes were The credit for inventing soap also goes to him. coloured by addition of colouring agents like He used mustard oil and some alkalies as metal oxides. ingredients for making soap. Indians began Copper metallurgy in India dates back to making soaps in the 18th century CE. Oil of the beginning of chalcolithic cultures in the Eranda and seeds of Mahua plant and calcium subcontinent. There are much archeological carbonate were used for making soap. evidences to support the view that technologies The paintings found on the walls of Ajanta for extraction of copper and iron were and Ellora, which look fresh even after ages, developed indigenously. testify to a high level of science achieved in According to Rigveda, tanning of leather ancient India. Varähmihir’s Brihat Samhita is and dying of cotton were practised during a sort of encyclopaedia, which was composed 1000–400 BCE. The golden gloss of the in the sixth century CE. It informs about the black polished ware of northen India could preparation of glutinous material to be applied not be replicated and is still a chemical on walls and roofs of houses and temples. It mystery. These wares indicate the mastery was prepared entirely from extracts of various with which kiln temperatures could be plants, fruits, seeds and barks, which were controlled. Kautilya’s Arthashastra describes concentrated by boiling, and then, treated the production of salt from sea. with various resins. It will be interesting to A vast number of statements and material test such materials scientifically and assess described in the ancient Vedic literature can them for use. Rationalised 2023-24 Unit 1.indd 2 9/9/2022 4:27:29 PM  Some Basic Concepts of Chemistry 3 A number of classical texts, like forces cause interaction between them. He Atharvaveda (1000 BCE) mention some conceptualised this theory around 2500 years dye stuff, the material used were turmeric, before John Dalton (1766-1844). madder, sunflower, orpiment, cochineal and Charaka Samhita is the oldest Ayurvedic lac. Some other substances having tinting epic of India. It describes the treatment of property were kamplcica, pattanga and jatuka. diseases. The concept of reduction of particle Varähmihir’s Brihat Samhita gives size of metals is clearly discussed in Charaka references to perfumes and cosmetics. Samhita. Extreme reduction of particle size is Recipes for hair dying were made from plants, termed as nanotechnology. Charaka Samhita like indigo and minerals like iron power, describes the use of bhasma of metals in the black iron or steel and acidic extracts of sour treatment of ailments. Now-a-days, it has rice gruel. Gandhayukli describes recipes been proved that bhasmas have nanoparticles for making scents, mouth perfumes, bath of metals. powders, incense and talcum power. After the decline of alchemy, Iatrochemistry Paper was known to India in the 17 th reached a steady state, but it too declined due century as account of Chinese traveller I-tsing to the introduction and practise of western describes. Excavations at Taxila indicate that medicinal system in the 20th century. During ink was used in India from the fourth century. this period of stagnation, pharmaceutical Colours of ink were made from chalk, red lead industry based on Ayurveda continued to and minimum. exist, but it too declined gradually. It took It seems that the process of fermentation about 100-150 years for Indians to learn was well-known to Indians. Vedas and and adopt new techniques. During this time, Kautilya’s Arthashastra mention about foreign products poured in. As a result, many types of liquors. Charaka Samhita also indigenous traditional techniques gradually mentions ingredients, such as barks of plants, declined. Modern science appeared in Indian stem, flowers, leaves, woods, cereals, fruits scene in the later part of the nineteenth and sugarcane for making Asavas. century. By the mid-nineteenth century, European scientists started coming to India The concept that matter is ultimately and modern chemistry started growing. made of indivisible building blocks, appeared in India a few centuries BCE as a part of From the above discussion, you have learnt philosophical speculations. Acharya Kanda, that chemistry deals with the composition, born in 600 BCE, originally known by the structure, properties and interection of matter name Kashyap, was the first proponent and is of much use to human beings in daily of the ‘atomic theory’. He formulated the life. These aspects can be best described and theory of very small indivisible particles, understood in terms of basic constituents of which he named ‘Paramãnu’ (comparable matter that are atoms and molecules. That to atoms). He authored the text Vaiseshika is why, chemistry is also called the science of Sutras. According to him, all substances are atoms and molecules. Can we see, weigh and aggregated form of smaller units called atoms perceive these entities (atoms and molecules)? (Paramãnu), which are eternal, indestructible, Is it possible to count the number of atoms spherical, suprasensible and in motion in and molecules in a given mass of matter and the original state. He explained that this have a quantitative relationship between the individual entity cannot be sensed through mass and the number of these particles? any human organ. Kanda added that there We will get the answer of some of these are varieties of atoms that are as different as questions in this Unit. We will further describe the different classes of substances. He said how physical properties of matter can be these (Paramãnu) could form pairs or triplets, quantitatively described using numerical among other combinations and unseen values with suitable units. Rationalised 2023-24 Unit 1.indd 3 9/9/2022 4:27:29 PM  4 chemistry 1.1 IMPORTANCE OF CHEMISTRY many big environmental problems continue to Chemistry plays a central role in science and be matters of grave concern to the chemists. is often intertwined with other branches of One such problem is the management of the science. Green House gases, like methane, carbon dioxide, etc. Understanding of biochemical Principles of chemistry are applicable processes, use of enzymes for large-scale in diverse areas, such as weather patterns, production of chemicals and synthesis of new functioning of brain and operation of a exotic material are some of the intellectual computer, production in chemical industries, challenges for the future generation of manufacturing fertilisers, alkalis, acids, salts, chemists. A developing country, like India, dyes, polymers, drugs, soaps, detergents, needs talented and creative chemists for metals, alloys, etc., including new material. accepting such challenges. To be a good Chemistry contributes in a big way to the chemist and to accept such challanges, one national economy. It also plays an important needs to understand the basic concepts of role in meeting human needs for food, chemistry, which begin with the concept of healthcare products and other material matter. Let us start with the nature of matter. aimed at improving the quality of life. This 1.2 Nature of Matter is exemplified by the large-scale production You are already familiar with the term matter of a variety of fertilisers, improved variety from your earlier classes. Anything which has of pesticides and insecticides. Chemistry mass and occupies space is called matter. provides methods for the isolation of life- Everything around us, for example, book, pen, saving drugs from natural sources and pencil, water, air, all living beings, etc., are makes possible synthesis of such drugs. composed of matter. You know that they have Some of these drugs are cisplatin and mass and they occupy space. Let us recall the taxol, which are effective in cancer therapy. characteristics of the states of matter, which The drug AZT (Azidothymidine) is used for you learnt in your previous classes. helping AIDS patients. Chemistry contributes to a large extent in 1.2.1 States of Matter the development and growth of a nation. With You are aware that matter can exist in three a better understanding of chemical principles physical states viz. solid, liquid and gas. it has now become possible to design and The constituent particles of matter in these synthesise new material having specific three states can be represented as shown in magnetic, electric and optical properties. This Fig. 1.1. has lead to the production of superconducting Particles are held very close to each other ceramics, conducting polymers, optical fibres, in solids in an orderly fashion and there is not etc. Chemistry has helped in establishing much freedom of movement. In liquids, the industries which manufacture utility goods, particles are close to each other but they can like acids, alkalies, dyes, polymesr metals, move around. However, in gases, the particles etc. These industries contribute in a big way are far apart as compared to those present in to the economy of a nation and generate solid or liquid states and their movement is employment. easy and fast. Because of such arrangement In recent years, chemistry has helped in of particles, different states of matter exhibit dealing with some of the pressing aspects the following characteristics: of environmental degradation with a fair (i) Solids have definite volume and definite degree of success. Safer alternatives to shape. environmentally hazardous refrigerants, (ii) Liquids have definite volume but do like CFCs (chlorofluorocarbons), responsible not have definite shape. They take the for ozone depletion in the stratosphere, have shape of the container in which they are been successfully synthesised. However, placed. Rationalised 2023-24 Unit 1.indd 4 9/9/2022 4:27:29 PM  Some Basic Concepts of Chemistry 5 Fig. 1.1 Arrangement of particles in solid, liquid Fig. 1.2 Classification of matter and gaseous state (iii) Gases have neither definite volume nor completely mix with each other. This means definite shape. They completely occupy particles of components of the mixture are the space in the container in which they uniformly distributed throughout the bulk of are placed. the mixture and its composition is uniform throughout. Sugar solution and air are the These three states of matter are examples of homogeneous mixtures. In interconvertible by changing the conditions contrast to this, in a heterogeneous mixture, of temperature and pressure. the composition is not uniform throughout Solid liquid Gas and sometimes different components are On heating, a solid usually changes to visible. For example, mixtures of salt and a liquid, and the liquid on further heating sugar, grains and pulses along with some changes to gas (or vapour). In the reverse dirt (often stone pieces), are heterogeneous process, a gas on cooling liquifies to the liquid mixtures. You can think of many more and the liquid on further cooling freezes to examples of mixtures which you come across the solid. in the daily life. It is worthwhile to mention here that the components of a mixture can 1.2.2. Classification of Matter be separated by using physical methods, In Class IX (Chapter 2), you have learnt that such as simple hand-picking, filtration, at the macroscopic or bulk level, matter can crystallisation, distillation, etc. be classified as mixture or pure substance. Pure substances have characteristics These can be further sub-divided as shown different from mixtures. Constituent particles in Fig. 1.2. of pure substances have fixed composition. When all constituent particles of a Copper, silver, gold, water and glucose are substance are same in chemical nature, it some examples of pure substances. Glucose is said to be a pure substance. A mixture contains carbon, hydrogen and oxygen in contains many types of particles. a fixed ratio and its particles are of same A mixture contains particles of two or composition. Hence, like all other pure more pure substances which may be present substances, glucose has a fixed composition. in it in any ratio. Hence, their composition is Also, its constituents—carbon, hydrogen variable. Pure substances forming mixture and oxygen—cannot be separated by simple are called its components. Many of the physical methods. substances present around you are mixtures. Pure substances can further be classified For example, sugar solution in water, air, into elements and compounds. Particles tea, etc., are all mixtures. A mixture may of an element consist of only one type of be homogeneous or heterogeneous. In a atoms. These particles may exist as atoms or homogeneous mixture, the components molecules. You may be familiar with atoms Rationalised 2023-24 Unit 1.indd 5 9/9/2022 4:27:30 PM  6 chemistry and molecules from the previous classes; however, you will be studying about them in detail in Unit 2. Sodium, copper, silver, hydrogen, oxygen, etc., are some examples of elements. Their all atoms are of one type. However, the atoms of different elements Water molecule Carbon dioxide are different in nature. Some elements, (H2O) molecule (CO2) such as sodium or copper, contain atoms Fig. 1.4 A depiction of molecules of water and as their constituent particles, whereas, in carbon dioxide some others, the constituent particles are molecules which are formed by two or more elements are present in a compound in a fixed atoms. For example, hydrogen, nitrogen and and definite ratio and this ratio is characteristic oxygen gases consist of molecules, in which of a particular compound. Also, the properties two atoms combine to give their respective of a compound are different from those of its molecules. This is illustrated in Fig. 1.3. constituent elements. For example, hydrogen and oxygen are gases, whereas, the compound formed by their combination i.e., water is a liquid. It is interesting to note that hydrogen burns with a pop sound and oxygen is a supporter of combustion, but water is used as a fire extinguisher. 1.3 Properties of Matter and their Measurement 1.3.1 Physical and chemical properties Every substance has unique or characteristic properties. These properties can be classified into two categories — physical properties, such as colour, odour, melting point, boiling point, density, etc., and chemical properties, like composition, combustibility, ractivity with Fig. 1.3 A representation of atoms and molecules acids and bases, etc. When two or more atoms of different Physical properties can be measured elements combine together in a definite ratio, or observed without changing the identity the molecule of a compound is obtained. or the composition of the substance. The Moreover, the constituents of a compound measurement or observation of chemical cannot be separated into simpler substances properties requires a chemical change to by physical methods. They can be separated occur. Measurement of physical properties by chemical methods. Examples of some does not require occurance of a chemical change. The examples of chemical properties compounds are water, ammonia, carbon are characteristic reactions of different dioxide, sugar, etc. The molecules of water substances; these include acidity or basicity, and carbon dioxide are represented in Fig. 1.4. combustibility, etc. Chemists describe, Note that a water molecule comprises interpret and predict the behaviour of two hydrogen atoms and one oxygen atom. substances on the basis of knowledge of their Similarly, a molecule of carbon dioxide physical and chemical properties, which are contains two oxygen atoms combined with determined by careful measurement and one carbon atom. Thus, the atoms of different experimentation. In the following section, we Rationalised 2023-24 Unit 1.indd 6 9/9/2022 4:27:30 PM  Some Basic Concepts of Chemistry 7 will learn about the measurement of physical properties. Maintaining the National Standards of Measurement 1.3.2 Measurement of physical properties The system of units, including unit Quantitative measurement of properties is definitions, keeps on changing with time. reaquired for scientific investigation. Many Whenever the accuracy of measurement of a properties of matter, such as length, area, particular unit was enhanced substantially volume, etc., are quantitative in nature. Any by adopting new principles, member nations quantitative observation or measurement is of metre treaty (signed in 1875), agreed represented by a number followed by units to change the formal definition of that in which it is measured. For example, length unit. Each modern industrialised country, of a room can be represented as 6 m; here, including India, has a National Metrology Institute (NMI), which maintains standards of 6 is the number and m denotes metre, the measurements. This responsibility has been unit in which the length is measured. given to the National Physical Laboratory Earlier, two different systems of (NPL), New Delhi. This laboratory establishes measurement, i.e., the English System experiments to realise the base units and and the Metric System were being used derived units of measurement and maintains National Standards of Measurement. These in different parts of the world. The metric standards are periodically inter-compared system, which originated in France in late with standards maintained at other National eighteenth century, was more convenient as Metrology Institutes in the world, as well it was based on the decimal system. Late, as those, established at the International need of a common standard system was felt Bureau of Standards in Paris. by the scientific community. Such a system was established in 1960 and is discussed in governmental treaty organisation created by a detail below. diplomatic treaty known as Metre Convention, 1.3.3 The International System of Units (SI) which was signed in Paris in 1875. The International System of Units (in The SI system has seven base units French Le Systeme International d’Unités and they are listed in Table 1.1. These units — abbreviated as SI) was established by pertain to the seven fundamental scientific the 11th General Conference on Weights and quantities. The other physical quantities, Measures (CGPM from Conference Generale such as speed, volume, density, etc., can be des Poids et Measures). The CGPM is an inter- derived from these quantities. Table 1.1 Base Physical Quantities and their Units Base Physical Symbol for Name of Symbol for Quantity Quantity SI Unit SI Unit Length l metre m Mass m kilogram kg Time t second s Electric current I ampere A Thermodynamic T kelvin K temperature Amount of n mole mol substance candela Iv cd Luminous intensity Rationalised 2023-24 Unit 1.indd 7 9/9/2022 4:27:30 PM  8 chemistry The definitions of the SI base units are These prefixes are listed in Table 1.3. given in Table 1.2. Let us now quickly go through some of The SI system allows the use of prefixes to the quantities which you will be often using indicate the multiples or submultiples of a unit. in this book. Table 1.2 Definitions of SI Base Units The metre, symbol m is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum Unit of length metre c to be 299792458 when expressed in the unit ms–1, where the second is defined in terms of the caesium frequencyV Cs. The kilogram, symbol kg. is the SI unit of mass. It is defined by taking the fixed numerical value of the planck constant h to Unit of mass kilogram be 6.62607015×10–34 when expressed in the unit Js, which is equal to kgm2s–1, where the metre and the second are defined in terms of c and V Cs. The second symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency V Cs, Unit of time second the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s–1. The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary Unit of electric ampere charge e to be 1.602176634×10–19 when expressed in the unit current C, which is equal to As, where the second is defined in terms of V Cs. The kelvin, symbol k, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value Unit of of the Boltzmann constant k to be 1.380649×10–23 when thermodynamic kelvin expressed in the unit JK–1, which is equal to kgm2s–2k–1 where temperature the kilogram, metre and second are defined in terms of h, c and V Cs. The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076×10 23 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol–1 and Unit of amount mole is called the Avogadro number. The amount of substance, of substance symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles. The candela, symbol cd is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation Unit of luminous Candela of frequency 540×1012 Hz, Kcd, to be 683 when expressed Intensity in the unit lm·W–1, which is equal to cd·sr·W–1, or cd sr kg–1 m–2s3, where the kilogram, metre and second are defined in terms of h, c and V Cs. Rationalised 2023-24 Unit 1.indd 8 9/9/2022 4:27:30 PM  Some Basic Concepts of Chemistry 9 Table 1.3 Prefixes used in the SI System Multiple Prefix Symbol 10–24 yocto y 10 –21 zepto z 10–18 atto a 10–15 femto f 10 –12 pico p 10 –9 nano n 10 –6 micro µ 10–3 milli m 10–2 centi c 10 –1 deci d 10 deca da 10 2 hecto h 103 kilo k 10 6 mega M Fig. 1.5 Analytical balance 109 giga G 10 12 tera T SI system, volume has units of m3. But again, 10 15 peta P in chemistry laboratories, smaller volumes 1018 exa E are used. Hence, volume is often denoted in 1021 zeta Z cm3 or dm3 units. 10 24 yotta Y A common unit, litre (L) which is not an SI unit, is used for measurement of volume 1.3.4 Mass and Weight of liquids. Mass of a substance is the amount of matter 1 L = 1000 mL, 1000 cm3 = 1 dm3 present in it, while weight is the force Fig. 1.6 helps to visualise these relations. exerted by gravity on an object. The mass of a substance is constant, whereas, its weight may vary from one place to another due to change in gravity. You should be careful in using these terms. The mass of a substance can be determined accurately in the laboratory by using an analytical balance (Fig. 1.5). The SI unit of mass as given in Table 1.1 is kilogram. However, its fraction named as gram (1 kg = 1000 g), is used in laboratories due to the smaller amounts of chemicals used in chemical reactions. 1.3.5 Volume Volume is the amont of space occupied by a Fig. 1.6 Different units used to express substance. It has the units of (length)3. So in volume Rationalised 2023-24 Unit 1.indd 9 9/9/2022 4:27:31 PM  10 chemistry In the laboratory, the volume of liquids fahrenheit) and K (kelvin). Here, K is the or solutions can be measured by graduated SI unit. The thermometers based on these cylinder, burette, pipette, etc. A volumetric scales are shown in Fig. 1.8. Generally, flask is used to prepare a known volume of a the thermometer with celsius scale are solution. These measuring devices are shown calibrated from 0° to 100°, where these two in Fig. 1.7. temperatures are the freezing point and the boiling point of water, respectively. The fahrenheit scale is represented between 32° to 212°. The temperatures on two scales are related to each other by the following relationship: 9 F  C  32 5 The kelvin scale is related to celsius scale as follows: K = °C + 273.15 It is interesting to note that temperature below 0 °C (i.e., negative values) are possible in Celsius scale but in Kelvin scale, negative Fig. 1.7 Some volume measuring devices temperature is not possible. 1.3.6 Density The two properties — mass and volume discussed above are related as follows: Mass Density = Volume Density of a substance is its amount of mass per unit volume. So, SI units of density can be obtained as follows: SI unit of density = kg = or kg m–3 m3 This unit is quite large and a chemist often expresses density in g cm–3, where mass is expressed in gram and volume is expressed in cm3. Density of a substance tells us about Fig. 1.8 Thermometers using different temperature scales how closely its particles are packed. If density is more, it means particles are more closely 1.4 Uncertainty in Measurement packed. Many a time in the study of chemistry, one 1.3.7 Temperature has to deal with experimental data as well as There are three common scales to measure theoretical calculations. There are meaningful temperature — °C (degree celsius), °F (degree ways to handle the numbers conveniently and Rationalised 2023-24 Unit 1.indd 10 9/9/2022 4:27:32 PM  Some Basic Concepts of Chemistry 11 present the data realistically with certainty to Reference Standard the extent possible. These ideas are discussed below in detail. After defining a unit of measurement such as the kilogram or the metre, scientists agreed 1.4.1 Scientific Notation on reference standards that make it possible As chemistry is the study of atoms and to calibrate all measuring devices. For getting molecules, which have extremely low masses reliable measurements, all devices such as metre sticks and analytical balances have and are present in extremely large numbers, been calibrated by their manufacturers a chemist has to deal with numbers as large to give correct readings. However, each of as 602, 200,000,000,000,000,000,000 for the these devices is standardised or calibrated molecules of 2 g of hydrogen gas or as small as against some reference. The mass standard 0.00000000000000000000000166 g mass of is the kilogram since 1889. It has been a H atom. Similarly, other constants such as defined as the mass of platinum-iridium Planck’s constant, speed of light, charges on (Pt-Ir) cylinder that is stored in an airtight particles, etc., involve numbers of the above jar at International Bureau of Weights magnitude. and Measures in Sevres, France. Pt-Ir was chosen for this standard because it is highly It may look funny for a moment to resistant to chemical attack and its mass write or count numbers involving so many will not change for an extremely long time. zeros but it offers a real challenge to do Scientists are in search of a new simple mathematical operations of addition, standard for mass. This is being attempted subtraction, multiplication or division with through accurate determination of Avogadro such numbers. You can write any two constant. Work on this new standard focuses numbers of the above type and try any one on ways to measure accurately the number of the operations you like to accept as a of atoms in a well-defined mass of sample. One such method, which uses X-rays to challenge, and then, you will really appreciate determine the atomic density of a crystal of the difficulty in handling such numbers. ultrapure silicon, has an accuracy of about This problem is solved by using scientific 1 part in 106 but has not yet been adopted to notation for such numbers, i.e., exponential serve as a standard. There are other methods notation in which any number can be but none of them are presently adequate to represented in the form N × 10n, where n is an replace the Pt-Ir cylinder. No doubt, changes exponent having positive or negative values are expected within this decade. and N is a number (called digit term) which The metre was originally defined as the varies between 1.000... and 9.999.... length between two marks on a Pt-Ir bar kept at a temperature of 0°C (273.15 K). In Thus, we can write 232.508 as 1960 the length of the metre was defined as 2.32508 × 102 in scientific notation. Note that 1.65076373 × 106 times the wavelength of while writing it, the decimal had to be moved light emitted by a krypton laser. Although to the left by two places and same is the this was a cumbersome number, it preserved exponent (2) of 10 in the scientific notation. the length of the metre at its agreed value. The metre was redefined in 1983 by CGPM Similarly, 0.00016 can be written as as the length of path travelled by light in 1.6 × 10 –4. Here, the decimal has to be vacuum during a time interval of 1/299 792 moved four places to the right and (–4) is the 458 of a second. Similar to the length and exponent in the scientific notation. the mass, there are reference standards for While performing mathematical operations other physical quantities. on numbers expressed in scientific notations, the following points are to be kept in mind. Rationalised 2023-24 Unit 1.indd 11 9/9/2022 4:27:32 PM  12 chemistry Multiplication and Division mass obtained by an analytical balance is These two operations follow the same rules slightly higher than the mass obtained by which are there for exponential numbers, i.e. using a platform balance. Therefore, digit 4 placed after decimal in the measurement by platform balance is uncertain. 5.6  10   6.9  10  = 5.6  6.9 10  5 8 58 The uncertainty in the experimental = 5.6  6.9  1013 or the calculated values is indicated by = 38..64  1013 mentioning the number of significant = 3.864  1014 figures. Significant figures are meaningful digits which are known with certainty plus 9.8  10   2.5  10  = 9.8  2.5 10    2 6 2  6 one which is estimated or uncertain. The = 9.8  2.5 10  2  6 uncertainty is indicated by writing the certain digits and the last uncertain digit. Thus, if we = 24.50  10 8 write a result as 11.2 mL, we say the 11 is = 2.450  10 7 certain and 2 is uncertain and the uncertainty would be +1 in the last digit. Unless otherwise 2.7  10 3 5  104 5.5   = 2.7  5.5 10 3  4 = 0.4909  10 7 stated, an uncertainty of +1 in the last digit is always understood. = 4.909  10 8 There are certain rules for determining the number of significant figures. These are Addition and Subtraction stated below: For these two operations, first the numbers are (1) All non-zero digits are significant. For written in such a way that they have the same example in 285 cm, there are three exponent. After that, the coefficients (digit significant figures and in 0.25 mL, there terms) are added or subtracted as the case are two significant figures. may be. (2) Zeros preceding to first non-zero digit Thus, for adding 6.65×104 and 8.95×103, are not significant. Such zero indicates exponent is made same for both the numbers. the position of decimal point. Thus, Thus, we get (6.65×104) + (0.895×104) 0.03 has one significant figure and Then, these numbers can be added as follows 0.0052 has two significant figures. (6.65 + 0.895)×104 = 7.545×104 (3) Zeros between two non-zero digits Similarly, the subtraction of two numbers can are significant. Thus, 2.005 has four be done as shown below: significant figures. (2.5 × 10–2) – (4.8 ×10–3) (4) Zeros at the end or right of a number are significant, provided they are on = (2.5 × 10–2) – (0.48 × 10–2) the right side of the decimal point. For = (2.5 – 0.48)×10–2 = 2.02 × 10–2 example, 0.200 g has three significant figures. But, if otherwise, the terminal 1.4.2 Significant Figures zeros are not significant if there is no Every experimental measurement has decimal point. For example, 100 has some amount of uncertainty associated only one significant figure, but 100 has with it because of limitation of measuring three significant figures and 100.0 has instrument and the skill of the person making four significant figures. Such numbers the measurement. For example, mass of an are better represented in scientific object is obtained using a platform balance notation. We can express the number and it comes out to be 9.4g. On measuring 100 as 1×102 for one significant figure, the mass of this object on an analytical 1.0×102 for two significant figures and balance, the mass obtained is 9.4213g. The 1.00×102 for three significant figures. Rationalised 2023-24 Unit 1.indd 12 9/9/2022 4:27:32 PM  Some Basic Concepts of Chemistry 13 (5) Counting the numbers of object, for Here, 18.0 has only one digit after the decimal example, 2 balls or 20 eggs, have infinite point and the result should be reported only significant figures as these are exact up to one digit after the decimal point, which numbers and can be represented by is 31.1. writing infinite number of zeros after placing a decimal i.e., 2 = 2.000000 or Multiplication and Division of 20 = 20.000000. Significant Figures In numbers written in scientific notation, In these operations, the result must be all digits are significant e.g., 4.01×102 has reported with no more significant figures as three significant figures, and 8.256×10–3 has in the measurement with the few significant four significant figures. figures. However, one would always like the results to be precise and accurate. Precision and 2.5×1.25 = 3.125 accuracy are often referred to while we talk Since 2.5 has two significant figures, about the measurement. the result should not have more than two Precision refers to the closeness of significant figures, thus, it is 3.1. various measurements for the same quantity. While limiting the result to the required However, accuracy is the agreement of a number of significant figures as done in the particular value to the true value of the above mathematical operation, one has to result. For example, if the true value for a keep in mind the following points for rounding result is 2.00 g and student ‘A’ takes two off the numbers measurements and reports the results as 1.95 1. If the rightmost digit to be removed is g and 1.93 g. These values are precise as they more than 5, the preceding number is are close to each other but are not accurate. increased by one. For example, 1.386. If Another student ‘B’ repeats the experiment we have to remove 6, we have to round and obtains 1.94 g and 2.05 g as the results it to 1.39. for two measurements. These observations 2. If the rightmost digit to be removed is are neither precise nor accurate. When the less than 5, the preceding number is not third student ‘C’ repeats these measurements changed. For example, 4.334 if 4 is to and reports 2.01 g and 1.99 g as the result, be removed, then the result is rounded these values are both precise and accurate. upto 4.33. This can be more clearly understood from the 3. If the rightmost digit to be removed is 5, data given in Table 1.4. then the preceding number is not changed Table 1.4 Data to Illustrate Precision if it is an even number but it is increased and Accuracy by one if it is an odd number. For example, Measurements/g if 6.35 is to be rounded by removing 5, we 1 2 Average (g) have to increase 3 to 4 giving 6.4 as the result. However, if 6.25 is to be rounded Student A 1.95 1.93 1.940 off it is rounded off to 6.2. Student B 1.94 2.05 1.995 1.4.3 Dimensional Analysis Student C 2.01 1.99 2.000 Often while calculating, there is a need to Addition and Subtraction of convert units from one system to the other. Significant Figures The method used to accomplish this is called The result cannot have more digits to the right factor label method or unit factor method of the decimal point than either of the original or dimensional analysis. This is illustrated numbers. 12.11 below. 18.0 Example 1.012 A piece of metal is 3 inch (represented by in) 31.122 long. What is its length in cm? Rationalised 2023-24 Unit 1.indd 13 9/9/2022 4:27:32 PM  14 chemistry Solution The above is multiplied by the unit factor We know that 1 in = 2.54 cm 1 m3 2 m3 2  1000 cm 3  6 3  3  2  10 3 m 3 From this equivalence, we can write 10 cm 10 1 in 2.54 cm Example = 1=