Atomic Structure and Spectroscopy PDF

Structure of Atom  Spectrum Electromagnetic spectrum or EM spectrum The arrangement obtained by arranging various types of EM waves in orders of their increasing frequency or decreasing wave length is called as EM SPECTRUM.  Energy increa...

Structure of Atom  Spectrum Electromagnetic spectrum or EM spectrum The arrangement obtained by arranging various types of EM waves in orders of their increasing frequency or decreasing wave length is called as EM SPECTRUM.  Energy increases Long Wavelength Short Wavelength Radio waves Microwaves Infrared Ultraviolet X-rays Gamma rays Cosmic 3 × 1014Å 3 × 109 Å 6 × 106Å 150Å 0.1Å 0.01Å 10-4Å Low frequency High frequency 7600Å 3800Å High Energy Low Energy Visible light The wavelength increase in the order Gamma rays < X–rays < UV rays < Visible < Infrared < Microwaves < Radio waves Hydrogen line spectrum or Hydrogen Spectrum When an electric excitation is applied on hydrogen atomic gas at Low pressure, the electron in lower orbits take energy and jumps to higher orbit. When these electron return (in 10–8 s) they release radiation or energy (bluish light) of different wavelengths. n=4 n=4 n=3 n=3 n=2 n=2 n=1 n=1 when a ray of this light is passed through a prism, a spectrum of several isolated sharp line is obtained. The wavelength of various lines show that spectrum lines lie in visible, Ultraviolet and Infrared region. These lines are grouped into different series.  ∞ 7 Q UV Visible IR IR IR IR 6 Humpherys series P 5 Pfund series O 0.31 eV 4 N Energy Levels Brackett series 0.66 eV 3 M Paschen series 1.89 eV 2 L Balmer series 10.2 eV 1 K Lyman series  Discovered Series Regions n2 → n1 No. of lines by n2 = 2,3,4... / n1 Lyman Lyman U.V. region n2 – 1 =1 Visible n2 = 3,4,5... / n1 Balmer Balmer n2 – 2 region =2 Infra red n2 = 4,5,6... / n1 Paschen Paschen n2 – 3 (I.R.) =3 n2 = 5,6,7... / n1 Brackett Brackett I.R. region n2 – 4 =4 n2 = 6,7,8... / n1 Pfund Pfund I.R. region n2 – 5 =5 Far I.R. n2 = 7,8,9... / Humphrey Humphrey n2 – 6 region n1=6 Calculation of Number of Spectral Lines Total number of spectral lines: = 1 + 2 + ……….(n2 – n1) (n2 − n1) (n2 − n1 + 1) = 2 If n1 = 1 (ground state) (n2 − 1) n2 (n − 1) n Total number of spectral lines = = 2 2 Number of spectral lines which falls in a particular series is : n2 – n1 Where , n2 = higher energy series n1 = lower energy series Example In a hydrogen spectrum if electron moves from 6th to 3rd orbit by transition in multi steps then find out the following steps : 1. Total number of lines in spectrum 2. Total number of lines in U.V. region 3. Total number of lines in visible region 4. Total number of lines in IR region 5. Number of lines in paschen region= 6. Number of lines in brackett region= 7. Number of lines in Pfund region=  Example In H atom if e- moves, from nth orbit to 1st orbit by transition in multi steps, if there are total number of lines in spectrum are 10 then find out the value of n ? Solution Ans : n = 5 Homework  Question In a hydrogen spectrum if electron moves from 6th to 2nd orbit by transition in multi steps then find out the number of lines in spectrum. Solution Ans : 10  Question In Balmer series of H atom spectrum which electronic transitions represents 3rd line ? Solution Ans : n2 = 5, n1 = 2