Rutherford Atomic Model was proposed by Physicist Earnest Rutherford to explain the atomic model in 1911. Till that date, only J.J Thomson’s atomic model was known. J.J Thomson’s model was lacking experimental evidences. It also did not have any scientific explanation as well as not accepted widely.
Rutherford performed an experiment in 1911 to predict the closer structure to atom. The experiment carried by him is widely known as alpha(α) scattering experiment. The observation and conclusion drawn from his experiment are summarized as Rutherford atomic model.
Rutherford Alpha Scattering Experiment
Alpha scattering experiment consists of a setup with a thin sheet of gold foil at the center, a radioactive source emitting α-particles and fluorescent screens.
The α-particles emitting from radioactive source were allowed to pass through a sheet of thin gold foil. The fluorescent screens were used to detect the deflection of α-particles on striking the gold foil.
The source of α-particles was Radium(Ra), a radioactive substances. Radium was placed in a lead shield with a small opening to prevent from radiations during the experimental procedures.
The α-particles emitting from radioactive source were allowed to passed through the slit of the lead screen which hits the thin gold foil. On hitting the foil, alpha particles were deviated in different directions. The fluorescent screens were adjusted in such a way that deviated rays falls on it. With the help of microscope, fluorescent screens were studied.
Image source: Britannica
- Rutherford observe that majority of α-particles passed straight through the foil without deviation.
- A few α-particles striking the gold foil were deflected through certain angles i.e. less than 90?.
- A very few alpha(α) particles turned back towards the source after striking the foil i.e. -180?.
- Majority of α-particles passed straight through the gold foil, Rutherford concluded that large part of an atom is empty or hollow.
- Deflection of few particles at angle less than 90? concluded that negative(-ve) charge particles are revolving around the circular path, known as electrons.
- A very few α-particles were deflected back towards the source. α-particles are beam of Helium nuclei. Since a very few of these particles are deflected back to its source, he concluded that small highly dense concentrated region exists at the center of atom.
- The highly dense region with positive charge were called nucleus.
Read also: Bohr's atomic model
Success of Rutherford Atomic Model
It leads to the discovery of nucleus.
Nucleus are positively charged & placed at the center of atom were conformed.
This model is used for determining the closest distance of approach between positively charged particles and stationary nucleus.
Limitation & drawback of Rutherford Model
This model could not explain atomic stability. According to Maxwell’s electromagnetic theory, a revolving electron should radiate energy continuously which makes electron to revolve in spiral path than in circular path. This results the electrons to finally fall into the nucleus which leads to the destruction of atoms.
Due to decrease in energy, the atom should give a continuous spectrum. But it failed to explain the formation of spectral lines.
FAQs on Rutherford model
a) Rutherford atomic model is based on?
Ans: It is experimental based model. The observation and conclusion drawn from α-scattering experiment by Rutherford is summarized in this model.
b) What are the successes of Rutherford atomic model?
Ans: The main success of this model is, it led to the discovery of nucleus.
c) Which radioactive substance was used in α-scattering experiment?
Ans: Radium(Ra) is used as radioactive substance which was a source of α-particle.
d) What are the limitations of Rutherford model?
This model was not able to explain the stability of atom and also failed to explain the formation of spectral lines.