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ATOMIC STRUCTURE STUDY MATERIAL & ASSIGNMENT

Apr 16, 2015

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Apex institute for IIT-JEE is the institution of making IITians in the Ghaziabad. It is the Institute in Indirapuram to making IITians (Eng..).
Its mission is to upgrade the teaching profession by providing high quality education and training to students who will be the industry's future engineers.

APEX INSTITUTE FOR IIT-JEE / AIEEE / PMT, 0120-4901457, +919990495952, +919910817866 www.apexiit .co.in/ CONTENTS 2.1 Composition of atom 2.2 Atomic number, Mass number and Atomic species 2.3 Electromagnetic radiations 2.4 Atomic spectrum- Hydrogen spectrum 2.5 Thomson's model 2.6 Rutherford's nuclear model 2.7 Planck's Quantum theory and Photoelectric effect 2.8 Bohrs atomic model 2.9 Bohr Sommerfelds model 2.10 Dual nature of electron 2.11 Heisenbergs uncertainty principle 2.12 Schrdinger wave equation 2.13 Quantum numbers and Shapes of orbitals 2.14 Electronic configuration principles 2.15 Electronic configurations of elements Assignment (Basic and Advance Level) Answer Sheet of Assignment Science has produced a microscopic structure of the atom, but its structure is so detailed and so subtle of something which is far removed from our immediate experience that it is difficult to see how many of its features were constructed. Yet among all the experiments used to form the theory of atomic structure, there stand a few which have been most in-fluential in shaping its major features. Erwin Schrdinger Chapt er 2 J oh n Da lt on 1808, believed that matter is made up of extremely minute indivisible particles, called atom which can takes part in chemical reactions. These can neither be created nor be destroyed. However, modern researches have conclusively proved that atom is no longer an indivisible particle. Modern structure of atom is based on Rutherfords scattering experiment on atoms and on the concepts of quantization of energy. 2. 1 Com p o s i t ion of a t om . The works of J .J . Thomson and Ernst Rutherford actually laid the foundat ion of the modern picture of the atom. It is now believed that the atom consists of several sub-atomic particles like electron, proton, neutron, positron, neutrino, meson etc. Out of these particles, the electron, proton and the neutron are called fundamental subatomic particles and others are non-fundamental particles. E El l e e c ct t r r o o n n ( ( 1 1e eo o) ) (1) It was discovered by J . J. Th om s on (1897) and is negatively charged particle. Electron is a component particle of cathode rays. (2) Cathode rays were discovered by W i lli am Cr ook e's & J . J. Th om s on (1880) using a cylindrical hard glass tube fitted with two metallic electrodes. The tube has a side tube with a stop cock. This tube was known as d i sch a r ge t u be. They passed electricity (10,000V) through a discharge tube at very low pressure (210 to ) 103Hg mm. Blue rays were emerged from the cathode. These rays were termed as Ca t h od e r a y s . (3) Pr oper t ies of Ca t h od e r a ys (i) Cathode rays travel in straight line. (ii) Cathode rays produce mechanical effect, as they can rotate the wheel placed in their path. (iii)Cathode rays consist of negatively charged particles known as electron. (iv) Cathode rays travel with high speed approaching that of light (ranging between 910 to 1110 cm/ sec) (v) Cathode rays can cause fluorescence. Gas at low pressure Cathode r ays Cathode Anode TC Vaccum pump High voltage + Discharge tube experiment for production of cathode rays APEX INSTITUTE FOR IIT-JEE / AIEEE / PMT, 0120-4901457, +919990495952, +919910817866 www.apexiit .co.in/ (vi) Cathode rays heat the object on which they fall due to transfer of kinetic energy to the object. (vii) When cathode rays fall on solids such as X Cu, rays are produced. (viii) Cathode rays possess ionizing power i.e., they ionize the gas through which they pass. (ix) The cathode rays produce scintillation the photographic plates. (x) They can penetrate through thin metallic sheets. (xi) The nature of these rays does not depend upon the nature of gas or the cathode material used in discharge tube. (xii) The e/ m (charge to mass ratio) for cathode rays was found to be the same as that for an e 810 76 . 1 ( coloumb per gm). Thus, the cathode rays are a stream of electrons. Note : q When the gas pressure in the discharge tube is 1 atmosphere no electric current flows through the tube. This is because the gases are poor conductor of electricity. q The television picture tube is a cathode ray tube in which a picture is produced due to fluorescence on the television screen coated with suitable material. Similarly, fluorescent light tubes are also cathode rays tubes coated inside with suitable materials which produce visible light on being hit with cathode rays. (4) R . S . Mu lli k an measured the charge on an electron by oil drop experiment. The charge on each electron is . 10 602 . 119C (5) Name of electron was suggested by J . S . S t on ey . The specific charge (e/ m) on electron was first determined by J . J. Th om s on . (6) Rest mass of electron is gm2810 1 . 9 1837 / 1 000549 . 0 amu of the mass of hydrogen atom. (7) According to Einsteins theory of relativity, mass of electron in motion is, m ] ) / ( 1 [ ) electron(m of mass Rest2c u Where u = velocity of electron, c= velocity of light. When u=c than mass of moving electron =. (8) Molar mass of electron = Mass of electron Avogadro number = . 10 483 . 54 (9) 1.12710 electrons =1gram. (10) 1 mole electron = 5483 . 0 mili gram. (11) Energy of free electron is 0. The minus sign on the electron in an orbit, represents attraction between the positively charged nucleus and negatively charged electron. (12) Electron is universal component of matter and takes part in chemical combinations. (13) The physical and chemical properties of an element depend upon the distribution of electrons in outer shells. (14) The radius of electron is . 10 28 . 412cm (15) The density of the electron is = mL g / 10 17 . 217 . Exa mp le : 1 The momentum of electron moving with 1/ 3rd velocity of light is (in g cm sec1) (a) 810 69 . 9 (b) 1010 01 . 8 (c) 1810 652 . 9 (d) None Solu t ion : (c) Momentum of electron, p = u m Where m is mass of electron in motion( )2/ 1 c um ; Also 3 / c u Momentum1 1810 28 10228sec 10 652 . 93 94 . 010 3 10 108 . 9310 33110 108 . 9

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cm gcc Exa mp le: 2 An electron has a total energy of 2 MeV. Calculate the effective mass of the electron in kg and its speed. Assume rest mass of electron 0.511 MeV. (a) 810 9 . 2 (b) 810 01 . 8 (c) 810 652 . 9 (d) None Solu t ion : (a) Mass of electron in mot ion amu9312 (1 amu = 931 MeV) kg2710 66 . 19312 kg3010 56 . 3 (1 kg amu2710 66 . 1 ) Let the speed of the electron be u. ( )2/ 1 c umm or 283028273010 3110 911 . 010 3110 66 . 1931511 . 010 56 . 3

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u u or 06548 . 010 3128 ,_

u or 93452 . 0 10 916 2 u or m u810 9 . 2 Exa mp le: 3 A electron of rest mass 2710 67 . 1 kg is moving with a velocity of 0.9c (c = velocity of light). Find its mass and momentum. (a) 1910 34 . 10 (b) 1010 01 . 8 (c) 1810 652 . 9 (d) None Solu t ion : (a) Mass of a moving object can be calculated using Einstens theory of relativity : ( )2/ 1 c umm m rest mass (given), u = velocity (given), c = velocity of light kgccm2722710 83 . 39 . 0110 67 . 1

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Momentum u m p ' ' 1 19 2710 34 . 10 9 . 0 10 83 . 3 ms kg c p P Pr r o o t t o o n n ( (1 1H H1 1, , H H+ +, , P P) ) Ex a m ples ba s ed on Ein s t ein s t h eor y of r elat i v i t y+ APEX INSTITUTE FOR IIT-JEE / AIEEE / PMT, 0120-4901457, +919990495952, +919910817866 www.apexiit .co.in/ (1) Proton was discovered by Gold s t ein and is positively charged particle. It is a component particle of anode rays. (2) Gold s t ein ( 18 8 6) used perforated cathode in the discharge tube and repeated Thomson's experiment and observed the formation of anode rays. These rays also termed as positive or canal rays. (3) Pr oper t ies of a n od e r a ys (i) Anode rays travel in straight line. (ii) Anode rays are material particles. (iii) Anode rays are positively charged. (iv) Anode rays may get deflected by external magnetic field. (v) Anode rays also affect the photographic plate. (vi) The e/ m ratio of these rays is smaller than that of electrons. (vii) Unlike cathode rays, their e/ m value is dependent upon the nature of the gas taken in the tube. It is maximum when gas present in the tube is hydrogen. (viii) These rays produce flashes of light on ZnS screen. (4) Charge on proton = 1910 602 . 1 coulombs = . . . 10 80 . 410u s e (5) Mass of proton = Mass of hydrogen atom= amu 00728 . 1 gram2410 673 . 1 1837 of the mass of electron. (6) Molar mass of proton = mass of proton Avogadro number 008 . 1 (approx). (7) Proton is ionized hydrogen atom ) ( +H i.e., hydrogen atom minus electron is proton. (8) Proton is present in the nucleus of the atom and it's number is equal to the number of electron. (9) Mass of 1 mole of protons is 1.007 gram. (10) Charge on 1 mole of protons is 96500 coulombs. (11) The volume of a proton (vol

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