Atomic Theory: Niels Bohr’s model

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The atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were developed. I am going to explain how Bohr’s model was produced.

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John Dalton was the first person who started the atomic theory. He was also the most popular person of atomic theory because he defined and confirm the atomic theory at that time, and it is very useful for now. John Dalton helped to revolutionize chemistry with his hypothesis that the behavior of matter could be explained using an atomic theory. In that time, he also created a list of the atomic theory which shows its circumscription of it. Dalton’s atomic theory has been created by John Dalton in 1807. After 100 years, Thomson found out that atoms include negatively charged particles called electrons. Thomson discovered electrons by doing the cathode-ray tube experiment. Cathode-ray tube experiment is a very famous experiment which was designed by Ferdinand Braun. Contemporaneous deflections by implemented electric and magnetic fields allowed Thomson to calculate the mass to charge ration of the particles composing the cathode ray. After 100 years, Ernest Rutherford found out Thomson make the mistake of electrons. Rutherford makes an experiment to confirm his saying was correct which is the gold foil experiment. Rutherford found out that an atom’s positive charge must be packed within a small region in its center, called the nucleus. Moreover, the positively charged particles in an atom’s nucleus is protons. 

After 100 years again, the last one, Niels Bohr corrected and found out some new things. Niels Bohr found out that electrons are found only in specific orbits around the nucleus, and the orbits in his model look like planets orbiting the sun, moreover, each possible electron orbit in Bohr’s model has fixed energy. He proposed a hydrogen-atom model that linked the atom’s electron to photon emission. The lower the orbit, the lower the energy level will be.

The energy level represents every orbit energy. If a photon comes into the lower orbit then the electron will get energy, an electron will jump to a higher energy level. But, if the electron back into the lower level, it will release energy. When a hydrogen atom is in an exciting standpoint, its electron is in one of the higher-energy boundaries. When the electron falls to a lower energy level, a photon is emitted, and the rule is called emission. Based on the different wavelengths of the hydrogen emission-line spectrum, Bohr calculated the allowed energy levels for the hydrogen atom.

Actually, after Bohr’s model, there is one more, called the cloud model. The Cloud model said that electrons move rapidly within a cloudlike region around the nucleus, but it isn’t popular because it was not confirmed by any experiment. Therefore, Bohr’s model of the hydrogen atom explained perceived spectral lines so well that many scientists concluded that the model could be applied to all atoms. However, Bohr’s approach did not explain the spectra of atoms with more than one electron.

Citation:

  1. MOTT, Vallerie. Introduction to Chemistry. ​Lumen​ [online]. [Accessed 12 November 2019]. Available from: https://courses.lumenlearning.com/introchem/chapter/john-dalton-and-atomic-theory/
  2. Discovery of the electron and nucleus. ​Khan Academy​ [online]. [Accessed 12 November 2019]. Available from: https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus
  3. The Nobel Prize in Chemistry 1908. ​NobelPrize.org​ [online]. [Accessed 12 November 2019]. Available from: https://www.nobelprize.org/prizes/chemistry/1908/rutherford/biographical/
  4. Emission Spectrum of Hydrogen​ [online]. [Accessed 12 November 2019]. Available from: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch6/bohr.html
29 April 2022

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