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  • IIT-JEE

    STRUCTUREOF ATOM

    C H E M I S T R YS T U D Y M A T E R I A L

    PHASE - I

    NARAYANA INSTITUTE OF CORRESPONDENCE COURSESF N S H O U S E , 6 3 K A L U S A R A I M A R K E TS A R V A P R I Y A V I H A R , N E W D E L H I - 1 1 0 0 1 6PH.: (011) 32001131/32/50 FAX : (011) 41828320Websi te : w w w . n a r a y a n a i c c . c o mE-mai l : i n f o @ n a r a y a n a i c c . c o m

  • 2004 NARAYANA GROUP

    This study material is a part of NARAYANA INSTITUTE OF CORRESPONDENCE COURSES for IIT-JEE, 2008-09. This is meant

    for the personal use of those students who are enrolled with NARAYANA INSTITUTE OF CORRESPONDENCE COURSES, FNS

    House, 63, Kalu Sarai Market, New Delhi-110016, Ph.: 32001131/32/50. All rights to the contents of the Package rest with

    NARAYANA INSTITUTE. No other Institute or individual is authorized to reproduce, translate or distribute this material in any form,

    without prior information and written permission of the institute.

  • PREFACEDear Student,

    Heartiest congratulations on making up your mind and deciding to be an engineer to serve the society.

    As you are planning to take various Engineering Entrance Examinations, we are sure that this STUDY PACKAGE isgoing to be of immense help to you.

    At NARAYANA we have taken special care to design this package according to the Latest Pattern of IIT-JEE, whichwill not only help but also guide you to compete for IIT-JEE, AIEEE & other State Level Engineering EntranceExaminations.

    The salient features of this package include :

    ! Power packed division of units and chapters in a scientific way, with a correlation being there.

    ! Sufficient number of solved examples in Physics, Chemistry & Mathematics in all the chapters to motivate thestudents attempt all the questions.

    ! All the chapters are followed by various types of exercises, including Objective - Single Choice Questions,Objective - Multiple Choice Questions, Comprehension Type Questions, Match the Following, Assertion-Reasoning& Subjective Questions.

    These exercises are followed by answers in the last section of the chapter including Hints & Solutions whereverrequired. This package will help you to know what to study, how to study, time management, your weaknesses andimprove your performance.

    We, at NARAYANA, strongly believe that quality of our package is such that the students who are not fortunateenough to attend to our Regular Classroom Programs, can still get the best of our quality through these packages.

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    THE NARAYANA TEAM

    ACKNOWLEDGEMENTWhile preparing the study package, it has become a wonderful feeling for the NARAYANA TEAM to get thewholehearted support of our Staff Members including our Designers. They have made our job really easy throughtheir untiring efforts and constant help at every stage.

    We are thankful to all of them.

    THE NARAYANA TEAM

  • CONTENTSCONTENTSCONTENTSCONTENTSCONTENTS

    STRUCTURE OF ATOM1. Theory

    2. Solved Problems

    (i) Subjective Type Problems

    (ii) Single Choice Problems

    (iii) Multiple Choice Problems

    (iv) Miscellaneous Problems

    Comprehension Type Problems

    Matching Type Problems

    Assertion-Reason Type Problems

    3. Assignments

    (i) Subjective Questions

    (ii) Single Choice Questions

    (iii) Multiple Choice Questions

    (iv) Miscellaneous Questions

    Comprehension Type Questions

    Matching Type Questions

    Assertion-Reason Type Questions

    (v) Problems Asked in IIT-JEE

    4. AnswersCO

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  • STRUCTURE OF ATOM

    IIT-JEE Syllabus Electron, proton and neutron; Constitution of nucleus, Properties of alpha, beta and gamma rays; Rutherfords scattering experiment; Bohrs atomic model (mathematical details excluded); Quantum numbers; Paulis exclusion principle; Hunds rule; Aufbau principle; Electronic configuration of elements (upto atomic number 36); Shapes of s, p, and dorbitals.

    CONTENTS

    Daltons Theory of atom

    Subatomic particles

    Various atomic models

    Photoelectric effect

    Particles & wave nature of electron

    Heisenberg uncertainty principle

    Schrodinger wave equation

    Quantum numbers

    Rules for filling electrons

    Shapes and size of orbitals

    Quantum mechanical treatment of Hatom

    INTRODUCTION The classical view of atomic structure was constructed with the body of knowledge accumulated in physics over several centuries. We begin with the focus on atomic nucleus with its protons and neutron. This includes obtaining atomic masses and atomic number. Electrons are at the heart of our modern view of atomic structure.

    This chapter, firstly provides experimental evidence for the picture of atom. After that it deals with nature of light and finally explains the behaviour of electrons in atoms leading to the modern view of atomic structure.

    FNS House, 63, Kalu Sarai Market, Sarvapriya Vihar, New Delhi-110016 Ph.: (011) 32001131/32 Fax : (011) 41828320

    1

  • NARAYANA INSTITUTE OF CORRESPONDENCE COURSES

    Chemistry : Structure of Atom

    1. DALTONS THEORY OF ATOM In 1807, John Dalton developed his atomic theory. According to this theory :

    An atom cannot be subdivided. Atoms are neither created nor destroyed during chemical reactions. Atoms of the same element are alike; in particular all atoms of an element have the

    same mass. Atoms of different elements are not alike; in particular, their masses are different.

    1.1 REASON FOR FAILURE OF DALTONS THEORY

    In 1833, Michael Faraday showed that there is a relationship between matter and electricity. This was the first major break through to suggest that atom was not a simple indivisible particle of all matter but was made up of small particles. Discovery of electrons, protons and neutrons discarded the indivisible nature of atom proposed by John Dalton.

    2. SUBATOMIC PARTICLES The researches done by various eminent scientists and the discovery of radioactivity have

    established beyond doubt, that atom is not the smallest indivisible particle but had a complex structure of its own and was made up of still smaller particles like electrons, protons, neutrons etc. At present about 35 different subatomic particles are known but the three particles namely electron, proton and neutron are regarded as the fundamental particles.

    We shall now take up the brief study of these fundamental particles.

    2.1 CATHODE RAYS (DISCOVERY OF ELECTRON) Gases are normally poor conductor of electricity at ordinary or high pressure. However

    when a tube filled with a gas is evacuated to a pressure of 0.01 mm Hg or lower and an electric potential is applied across a pair of electrodes into the tube discharge takes place between the electrodes during which a stream of rays moves from cathode to anode, William Crookes (1879) called these rays as cathode rays.

    2.1a PROPERTIES OF CATHODE RAYS

    1. Cathode rays travel in straight lines with a high speed approaching to that of light. Their linear propagation is shown by the fact that they caste shadows of the solid objects placed in their path.

    2. They produce temperature rise in any object they strike. 3. They pass through thin films of metals but are stopped by thicker foils. 4. Cathode rays can produce mechanical effect e.g. when allowed to fall on a small

    paddle wheel they cause rotation of wheel. This experiment shows that cathode rays consist of material particles.

    FNS House, 63, Kalu Sarai Market, Sarvapriya Vihar, New Delhi-110016 Ph.: (011) 32001131/32 Fax : (011) 41828320

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  • Chemistry : Structure of Atom

    NARAYANA INSTITUTE OF CORRESPONDENCE COURSES

    5. The cathode rays can be deflected by electric and magnetic field. The direction of deflection is always such that these particles bear a negative charge.

    6. Finally no matter what the nature of the cathode or the gas in the discharge tube, the negatively charged particles are always the same as reflected by the same e/m ratio by J.J. Thomson.

    These particles constituting cathode rays have been named electron by J.J. Thomson. The fact that electrons are independent of the nature of source from which they come suggest that they are constituent of all elements.

    Thomson determined e/m ratio of electrons by applying electric and magnetic field

    2.1b METHOD OF EXPERIMENTAL DETERMINATION OF E/M

    Anode +(metal plugs with slits)

    Tube was evacuatedthrough here and thensealed off.

    Cathode Cathode ray

    Scale pasted on outside of tubeto measure deflection of cathode ray

    3 Magnetic only1 Both or neither2 Electric only

    Aluminum plates(5 cm 2 cm, 1.5 cm apart)

    Determination of ratio of electronem

    em

    of electron = 1.7588 = 1.7588 1110 C/ kg 810 C / g

    2.1C DETERMINATION OF CHARGE OF ELECTRON

    An American physicist R. A. Millikan determined charge on electron by oil drop experiment Charge on electron = 1. coulombs, from the data obtained from the above two experiments, mass of electron can be calculated.

    196022 10

    28em 9.1 10 gem

    = =

    Eyepiece of telescopewith three equally spacedcrosshairs

    Telescope (low-power magnifier)

    Brass plates 22 cm indiameter and 1.6 cm apart

    Drop under observation

    Oil was spr