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TELANGANA STATE MODEL SCHOOL & Jr. COLLEGE, Vill: Peddapur, Mdl: Julapally, Dist: Peddapally-505415, CHEMISTRY NOTES |* YEAR, , 1. ATOMIC STRUCTURE (8M), , Q: What are postulates of Bohr's model of hydrogen atom?, Discuss the importance of this model to explain various series of, line spectra in hydrogen atom., , (8M), , , , Ans: I. Postulates of Bohr's model, , » Electron in an atom revolve around nucleus in certain fixed, circular paths called orbits., , » Each orbit has fixed amount of energy. So these orbits are also, called energy levels., These orbits are denoted by 1,2,3,4..... (or) K,L,M,N......, , > As long as an electron revolves around the, , 4 ~— <n snew, nucleus in a fixed orbit it does not emit 1. ne, (or) absorb energy. So these orbits are also 1X NVA. shen, called as Stationary orbits. eo TT —, > Angular momentum of revolving electron :, zs ‘ E z e h a, is quantised and is an integral multiple mm ., , nh ” “i a, mvr =>. Here, m= mass of electron, v = velocity, r = radius, TT, , and h = Plank’s constant., , > Energy is emitted (or) absorbed when electron jumps from one, orbit to another orbit., The energy difference between two orbits is AE = E2-E, =hv, Here, E, = Energy of the higher orbit, E; = Energy of the lower, orbit., , II. Hydrogen spectrum — Bohr’s explanation:
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** When electric discharge is passed through gaseous hydrogen,, the electron in atoms absorb energy., , “* Then they jump into higher energy orbits., , “+ In higher orbits, the energy is more but stability is less., , “* Than the excited electrons comes back to lower orbits in one or, multiple steps., , “* Energy is released during this process and it appears in the, form of spectral lines., , “+ When an electron jumps from any higher orbit to, i) n=l produces spectral lines "==, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , in the UV region. This nel, named as Lyman series. =, ii) n=2 produces spectral lines "= “Phang, in the visible region. Thisis *=+ aa, named as Balmer series. ate, iii) n=3,4,5 produces spectral = “Paschen, lines in near IR, IR, far IR a, regions. ce, These are named as Paschen, a ———————, brackett and Pfund-series few, respectively, , spectral lines for hydrogen, , , , , , , , , , , , , , , , , , , , , , , , series ny Ny go, Lyman 1 2,3 uV, Balmer 2 3,4.. | Visible, Paschen 3 4,5 IR, Brackett 4 5,6 IR, Pfund 5 6,7. IR
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1 a, , i 1, From the Rydberg equation, wavenumber v = a= [5 — 5], d., 2, , , , Q: Write Bohr’s model limitations. Give any two differences, between emission and absorption spectra., , Y Bohr’s theory fails to explain the fine spectrum of hydrogen., , Y Bohr’s theory fails to explain the Spectre of multi electron, atoms like He, Li, Be etc.,, , Y Bohr’s theory could not explain the Zeeman effect., , Y Bohr’s theory could not explain the Stark effect, , Y Bohr’s theory could not explain the ability of atoms to form, molecules by chemical bonds., , Y Itis against to de-Broglie’s wave nature and Heisenberg’s, uncertainty principle., , v It fails to explain doublets of the spectral lines., , Difference between the Emission Spectrum and Absorption Spectrum, , , , , , , , , , Emission Spectrum Absorption Spectrum, , 1) It is produced due to the 1) Itis produced due to the, emission to energy by an absorption of energy by a, excited substance. substance., , 2) It is produced when electrons 2) Itis produced when electrons, jump from higher to lower jump from lower orbit to, orbits. higher orbits., , 3) It has bright line on dark 3) it has dark lines on bright, background. background., , , , Q: How are the quantum numbers n, | and m, arrived at? Explain, the significance of these quantum numbers., , Ans: A set of numbers that are used to describe the energy levels of, an atom is called Quantum numbers., , The quantum numbers n, | and m, are arrived by solving Schrodinger, wave equation. They explain, , (i) The position of electron in space around the nucleus.
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(ii), , Various orbitals which are distinguished by their size,, shape and orientation., , 1) Principal quantum number (n ), , (i), , (ii), (iii), (iv), , (v), , It was proposed by Bohr., , It was denoted by ‘n’., , The values of ‘n’ are 1,2,3,4...... (or) K,L,M.N....., Significance: The value of ‘n’ indicates, , (a) the size of the orbit(r,) (b) energy of the orbit (E,), The maximum number of electrons in n"™ orbit = 2n”, , 2) Azimuthal quantum number (1 ), , (i), , (ii), (iii), (iv), , (vy), , (vi), , It was proposed by Sommerfeld, , It was denoted by ‘I’., , The values of ‘I’ are 0,1,2,3.....(n-1), , Significance: The value of ‘1’ indicates, , a) Shape of the orbitals. b) angular momentum of, , , , , , , , , , , , , , , , , , , , , , electron Principal Quantum 7 Value Name of the Sub shells, , The ‘I’ values 0,1,2.3 Number (n) I — 1 or Orbitals, correspond to the sub , 0 7, shells s,p,d,f respectively. 2 1 2p, The shape of s-orbital is 9 3s, spherical, the shape of p- 3 d 3p, orbital is dumb-bell, the Z 3d, shape of d-orbital double ° ‘s, dumd-bell, the shape of 7 - “, the f-orbitals is four fold ; =, dumb-bell., , , , , , , , , , , , 3) Magnetic quantum number ( m or ml ), , (i), , (ii), (iii), (iv), , (vy), , It was proposed by Lande, , It is denoted by ‘m/’ (or) my, , The values of the ‘m’ range from —I to +] including ‘0’., For a given value of ‘I’, the total number of ‘m’ values =, (21+1), , Significance: The value of the ‘m’ indicates the, orientation of the orbital in space., , It explains the Zeeman and Stark effect.
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Shell | Subshell | Subshell Orientation Number of, ” Zz Notation m Orbitals, 1 ° 1s ° 1, 2 ° 2s ° 1, , 1 2p -1 0 +1 3, 3 ° 3s ° 1, 1 3p -1 0 41 3, 2 3d -2 -1 0 +1 42 5, 4 oO as Oo 1, 1 4p -1 0 +1 3, 2 4d -2 -1 0 +1 +2 5, 3 af -3 -2 -1 0 +1 +2 43 x, , , , , , , , , , , , , , , , 4) Spin quantum number (s ), , (i) It was proposed by uhlenbeck and Goudsmith., (ii) It is denoted by ‘s’., , (iii) The value of ‘ s’ are + ; and - >, , (iv) Significance: It explains spin of electrons.
