Rutherford Model of Atom
The idea of atom originated in ancient Greek and Indian cultures. The term atom was first coined by Democritus around 370 BC and defined it as the entity which is eternal, uncreated, and infinite in number. He stated that all objects in this universe is made of atoms, and their characteristics determine the qualities of the object itself.
After the genesis of this idea, many philosophers and scientists gave their own version of Atomic theory. The idea was even lost for a few centuries and was rediscovered by John Dalton at the end of the 18th century. Dalton even postulated some laws so as to justify the reasons behind chemical reactions.
With time rolling, new discoveries were made in this field. J.J Thomson was one such pioneer who not only discovered electron but also gave the first model of the atom which came to be known as the Plum Pudding Model. This model was based on then considered hypothesis that atoms are neutral in charge. So, when Thomson discovered electrons, he proposed that electrons are like plums that are embedded in a pudding of positive charge.
Later in the early 20th century (1908-1913), Hans Geiger and Ernest Marsden conducted the famous Gold Foil Experiment under the guidance of Ernest Rutherford. Rutherford was the student of J.J Thomson, and through his gold foil experiment proved that the plum pudding model is incorrect.
Gold Foil Experiment
When Rutherford discovered Protons, there was a need to update the existing model of atom as well. He conducted an experiment to determine the positions of subatomic particles in the atom. He along with Hans Geiger and Ernest Marsden conducted the Gold foil experiment.
In this experiment, rutherford bombarded high energy alpha particles on a very gold foil. He surrounded the gold foil with zinc sulfide screens to observe the deflections produced.
The observations made from this experiment are described below:
- A large portion of the alpha beam passed through gold foil without getting deflected. This suggests that a major portion of the atom is empty.
- Just a fraction of alpha particles were deflected during this experiment suggesting that positive charge is not evenly distributed in the atom as assumed in the Plum Pudding model. But rather, it is concentrated over a very small area.
- The third observation made was that only very few alpha particle rays were deflected back at 180°. That means the volume of positive charge occupied in the atom is very small in comparison to the total volume of the atom itself.
Postulates of Rutherford Model of Atom
- Atom is composed of negatively and positively charged particles called electrons and protons. The majority of the mass is concentrated at the center of the atom known as the nucleus.
- Electrons revolve around the nucleus at a very high speed in a fixed path known as orbits.
- Atoms are electrically neutral and the electrostatic attraction holds the electrons and protons together
- The volume occupied by the nucleus is very small in comparison to the volume occupied by atom.
Drawbacks of Rutherford Model of the Atom
The atomic model proposed by Rutherford is analogous to the solar system where the nucleus is like Sun and electrons are like planets revolving around it. But, this model failed to align with Clark Maxwell’s electromagnetic principles. According to this principle, a charged body moving under the influence of attractive forces loses energy continuously in the form of electromagnetic radiation. So, electrons are a charged body and it should emit radiations while revolving around the nucleus. As a result of this, the electrons should lose energy at every turn, moving closer and closer to the nucleus and ultimately collapse. According to Maxwell’s calculations, it should take 10-8 seconds for an electron to collapse in the nucleus.
- However, this never happens. Thus, the Rutherford model of atom failed to explain the Stability of atom.
- The Rutherford model of the atom also failed to explain the structure of atoms.
- Furthermore, the model also failed to explain the existence of certain definite lines in the hydrogen spectrum. If the electrons were to lose energy continuously, the atomic spectrum of hydrogen should have been continuous. However, the spectrum of hydrogen is found to be discontinuous in the form of characteristics lines of definite wavelengths.
Summarized Notes On Rutherford Model Of Atom
- J.J Thomson discovered electrons. He also proposed the plum pudding model.
- Ernest Rutherford discovered protons and through his Gold foil experiment proposed a new model of the atom.
- The new model of the atom that Ruderford proposed resembles the solar system.
- Most of the volume in an atom is empty.
We hope the above furnished article on Rutherford Model of Atom has helped you understand this important concept.
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