Assess the limitations of the Rutherford and Bohr atomic models
Limitations of Rutherford atomic model:
- If the electrons were orbiting the nucleus in the center, they would have to accelerate and thus give out electromagnetic radiation and energy according to Maxwell’s Theory of electromagnetism.
- As electrons lose energy and spiral inwards, the frequency of EM waves emitted would steadily change. This was never observed.
- Electrons according to this model would lose energy in the form of Electromagnetic radiation and thus the atom would collapse.
- Excited atoms emitted radiation but the frequencies were discreet and characteristic of the atoms. This couldn’t be explained with Rutherford’s model.
Limitations of Bohr’s atomic model:
Although Bohr’s model was able to incorporate the quantum nature of atoms, it had the following limitations:
- The emission spectra of atoms had discrete frequencies. It wasn’t possible to calculate these frequencies for atoms other than Hydrogen, using Bohr’s model.
- Bohr’s model worked well with atoms which had only one electron in its outer shell, but failed for other atoms.
- The discrete spectrum showed that the frequencies varied in intensity, which meant that certain electron transmissions were more favoured than others. Bohr’s model couldn’t explain this.
- On careful observations with powerful instruments it was found that the discrete frequencies had small shifts and further splittings called hyperfine structure splitting or hyperfine splitting. These couldn’t be explained using Bohr’s model either.
- It was found that discrete frequencies from emission spectrum split up when a gas was excited within a magnetic field. This phenomenon known as Zeeman effect, couldn’t be explained with Bohr’s model.
Extract from Physics Stage 6 Syllabus © 2017 NSW Education Standards Authority (NESA)