What Was Hantaro Nagaoka Atomic Theory?


Diego Sanchez

Hantaro Nagaoka’s atomic theory is one of the earliest models of the atomic structure. This Japanese physicist proposed his model in the year 1904, which was further developed by Niels Bohr in 1913.

The Nagaoka model or the Saturnian model of the atom was an improvement over J.J. Thomson’s Plum pudding model. In this article, we’ll take a closer look at Hantaro Nagaoka’s atomic theory and how it contributed to the development of modern atomic science.

The Plum Pudding Model

Before diving into Nagaoka’s atomic theory, let’s first discuss J. According to this model, an atom is a sphere of positive charge with negatively charged electrons (or plums) embedded within it. However, this model couldn’t explain why electrons don’t fall into the nucleus due to electrostatic attraction.

The Saturnian Model

Nagaoka proposed his atomic theory as a solution to this problem. According to his theory, an atom consists of a positively charged central nucleus surrounded by rotating electrons in concentric rings or orbits. The electrons move in circular paths around the nucleus just like Saturn’s rings revolve around its planet.

This model explained why electrons don’t fall into the nucleus due to electrostatic attraction. The centrifugal force generated by their motion balances out the attractive force between electrons and protons in the nucleus.

Limitations of Nagaoka’s Atomic Theory

Although Nagaoka’s Saturnian model provided an explanation for why atoms don’t collapse under electrostatic forces, it had some limitations:

  • It couldn’t explain why atoms emit light when heated or excited.
  • It couldn’t explain why atoms have discrete energy levels.
  • It couldn’t explain why some elements emit characteristic X-rays.

Bohr’s Atomic Model

Niels Bohr, a Danish physicist, built on Nagaoka’s atomic theory and proposed a new model in 1913. According to Bohr’s atomic model, electrons occupy certain discrete energy levels or orbits around the nucleus.

When excited, an electron can move from a lower energy level to a higher one by absorbing energy. Similarly, when it returns to its original energy level, it emits energy in the form of light.

Bohr’s atomic model explained the limitations of Nagaoka’s Saturnian model and laid the foundation for modern atomic science.


In conclusion, Hantaro Nagaoka’s atomic theory was an essential step in the development of modern atomic science. His Saturnian model provided a solution to Thomson’s Plum pudding model and opened doors for further research in this field. Although Bohr’s atomic model replaced Nagaoka’s model, his contribution to this field remains significant and noteworthy.