11th Class Chemistry Structure of Atom / परमाणु संरचना

  • question_answer 139)
      When an electric discharge is passed through hydrogen gas, the hydrogen molecules dissociate to produce excited hydrogen   atoms.   These   excited   atoms   emit electromagnetic radiation of discrete frequencies which can be given by the general formula \[\overline{v}=109677\left[ \frac{1}{n_{i}^{2}}-\frac{1}{n_{f}^{2}} \right]\] What points of Bohr's model of an atom can be used to arrive at this formula? Based on these points derive the above formula giving description of each step and each term.

    Answer:

      Thus, the different spectral lines in the spectra of atoms correspond to different transitions of electrons from higher energy levels to lower energy levels. Let \[{{n}_{1}}\] and \[{{n}_{2}}\] be the two energy shells in the hydrogen atom \[({{n}_{1}}<{{n}_{2}})\] According Bohr atomic model: Energy associated with \[{{n}_{1}}\] shell \[=-\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{n_{1}^{2}{{h}^{2}}}\] Energy associated with \[{{n}_{2}}\]  shell \[=-\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{n_{2}^{2}{{h}^{2}}}\] \[{{E}_{{{n}_{2}}}}-{{E}_{{{n}_{1}}}}=-\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{n_{2}^{2}{{h}^{2}}}-\left[ -\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{n_{1}^{2}{{h}^{2}}} \right]\] \[\Delta E=\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{{{h}^{2}}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] \[\Delta E=hv=h\cdot \frac{c}{\lambda }\] \[h\cdot \frac{c}{\lambda }=\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{{{h}^{2}}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\]                 or            \[\frac{1}{\lambda }=\frac{2{{\pi }^{2}}m{{e}^{4}}{{k}^{2}}}{{{h}^{3}}c}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\]                                 \[\frac{1}{\lambda }=\overset{\_}{\mathop{v}}\,={{R}_{H}}\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\]                 here      \[\overset{\_}{\mathop{v}}\,\] = wave number or            \[v={{R}_{H}}\times c\left[ \frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}} \right]\] where \[{{R}_{H}}\] is Rydberg constant for hydrogen. Its value is\[109677.76c{{m}^{-1}}\]


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