Ernest Rutherford – The nuclear atom
Today we’re going to be looking at Rutherford’s alpha-particle scattering experiment and how, through this, he found ground-breaking new evidence on the structure of a nuclear atom.
Ernest Rutherford, a notable English physicist, in the 20th century understood that all matter is made up of atoms. However, he wanted to delve deeper in this understanding about atoms. As a result in 1909, along with his assistants, Hans Geiger and Ernest Marsden, carried out an experiment to investigate a detailed model for the atom (the ‘inner-workings’).
Diagram of Rutherford’s Alpha-Particle Scattering Experiment
What Rutherford did was quite unique. He used and a He used a source which emitted alpha particles (charged helium ions), and directed the beam of alpha particles towards a thin gold foil (he wanted a thin layer as thin a layer as possible) to observe any effects between the two.
- Roughly 99% of the alpha particles passed straight through the foil.
- Some of the alpha particles were deflected by the foil at small angles - 1 in 8000 alpha particles were deflected at around 90° and over.
- Around one out of every 12000 particles to rebounded off the gold foil – some directly in the opposite direction!
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Rutherford stated that:
“It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
Rutherford’s Explanation about the Observations
Rutherford inferred from the observations that there must be a positive charge in the atom due to the fact that the alpha particles, which were repelled, were positively-charged (as similar charges repel each other and cause them to scatter in the opposite/a different direction. Also, the observations implied that the ‘positively-charged something’ in the atom must also have a high mass. The high mass, within the atom, enabled the ‘something’ to withstand the charged alpha particles that were fired onto the foil at such energy – if it did not have a high mass then no alpha particles would have been deflected.
By gathering all the observations and his inferred theories about the ‘innards’ of the atoms he came up with a model.
Rutherford’s Nuclear Model of the Atom
Rutherford came up with a model for the atom from his creative thinking about the observations. What he deduced is that there must a nucleus in an atom - a nucleus that is positively-charged but also has a high mass (repelling and withstanding observations). When he further analysed his data he also came to the conclusion that as 99% of the alpha particles flew straight through the gold foil, the nucleus must be very small – much smaller than the width of an atom (the diameter of the nucleus is around a hundredth-thousandth of the diameter of the atom).
Why a Scientist must use Imagination to Explain Observations
A scientist must use creative thinking as well as his background knowledge when interpreting findings from the investigations or experiment. Through this he/she can deduce and infer from analysing their data on how such and such a model works (i.e. Rutherford). A large part of coming up with scientific hypothesis requires creative thought. It is necessary for scientists to always use their imagination in a scientific investigation. The real purpose of conducting an investigation is to comprehend something by using something audacious and outward. A scientist uses their knowledge towards something that is not fully analyzed per se, but they have to use current knowledge and imagination together in order to come up with a good answer.
What makes Rutherford’s Explanation Good?
What Rutherford did what that he collected all that he observed, and thoroughly analysed his results. By doing so he could filter out the different explanations and combine them all into one – which is his model. Simply put, all of the data he collected is accounted through his explanation, and his explanations are pieced together by the data he collected.
His explanations could be tested in different ways. What can be done is by testing the explanation with different foils. In today’s day-and-age, science has advanced much more than in Rutherford’s time. Through this, different (positively-charged) particles can be used to fire at different types of foils to see if the explanation is true for all. As all matter is made of atoms, then the observations in the different explanations must be similar to that of Rutherford’s observations. Predictions can be made through this – i.e. by stating that particles should deflect or rebound or pass through when fired. Also, predictions can be made by seeing what to expect when using an electron microscope to outline some-type of structure within the atom. At a specialist-research facility in Switzerland (CERN), they use particle-accelerators in order to make atoms collide. This enables scientists to see the structure within. All of this can be done by making predictions about the structure of atoms using Rutherford’s explanation about the nuclear model of an atom.