Rutherford Scattering Experiment
- Updated by Scienly
- On September 10, 2024
In this chapter, we will understand Rutherford’s scattering experiment and its observations and conclusions. In order to understand the arrangement of charged particles like electrons and protons in an atom, the British scientist, Ernest Rutherford and his co-workers in 1911 carried out a series of experiments using alpha particles known as Rutherford’s alpha scattering experiments. This experiment is based on the alpha particles (helium nuclei) experiment.
The Rutherford’s alpha particle scattering experiment is one of the most important experiments in the history of atomic physics. It laid the foundation for the modern understanding of the atom, challenging earlier models and introducing the concept of an atomic nucleus.
Before Rutherford’s experiment, J. J. Thomson had given the first model of an atom in 1904, also known as “plum pudding model of atom”. In this model, he proposed that an atom may be considered as a sphere of positively charge particles in which the negatively charged particles called electrons are embedded to make the atom as a whole neutral.
This model was discarded in 1911 on both theoretical and experimental due to the Rutherford’s atomic model. Now let’s understand Rutherford scattering experiment step by step.
Rutherford’s Alpha Particle Scattering Experiment
In this experiment, Ernest Rutherford bombarded a beam of alpha particles with a very thin gold foil. The thickness of gold foil is approximately 0.00006 cm. The alpha particles were emitted from the radioactive substances such as radium or polonium. An alpha particle is a doubly ionized helium atoms or ions with two units of positive charge, mass number is equal to 4 and missing two electrons. It is represented as +2 He 4 or +2 α 4 .
The pictorial representation of Rutherford’s scattering experiment is shown in the below figure.
From the above figure, it is clear that he produced a narrow beam of alpha particles from a radioactive substance like radium placed in a lead block and then passed it through a thin sheet of gold foil. A movable circular screen coated with Zinc Sulphide (ZnS) screen is placed around the gold foil in order to detect alpha particles after scattering.
When these alpha particles hit the screen, it produced a tiny flash of light (scintillation) on the screen, which could be observed through movable a microscope.
Observations from Alpha Particle Scattering Experiment
The following observations were made from the alpha particle scattering experiment:
- Most of the alpha particles (nearly 99%) passed through the gold foil with little to no deflection. In other words, most of the alpha particle moved in the straight path with no deflection. This means that most of the space inside the atom is empty, as shown in the above figure.
- Some of the alpha particles deflected with small angle, meaning that the positive charge of an atom occupies a tiny space.
- A very few alpha particles (approx. 1 in 20,000) deflected back through the deflection of 180 degrees. This means that the whole positive charge and mass of the atom is concentrated in a very small volume inside the atom.
Thomson’s atomic model could not explain these observations. According to Thomson’s model of atom, positive charge and mass inside an atom are uniformly distributed throughout its volume.
Conclusion from Rutherford Scattering Experiment
After performing a series of scattering experiments, Rutherford concluded that:
- Most of the space inside an atom is empty because most of the alpha particles passed through the gold foil undeflected.
- There must be the presence of a heavy positively charged mass at the center of an atom because some of the alpha particles are deflected by a certain angle.
- A heavy positively charged mass at the center of the atom is very small, which he named as nucleus.
On the basis of these observations, Sir Ernest Rutherford proposed the nuclear model of atom, which you will study in the next chapter.
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The prevailing model of atomic structure before Rutherford's experiments was devised by J. J. Thomson. [1]: 123 Thomson had discovered the electron through his work on cathode rays [2] and proposed that they existed within atoms, and an electric current is electrons hopping from one atom to an adjacent one in a series.There logically had to be a commensurate amount of positive charge to ...
Simulate the famous experiment in which he disproved the Plum Pudding model of the atom by observing alpha particles bouncing off atoms and determining that they must have a small core. How did Rutherford figure out the structure of the atom without being able to see it? Simulate the famous experiment in which he disproved the Plum Pudding ...
The nucleus was postulated as small and dense to account for the scattering of alpha particles from thin gold foil, as observed in a series of experiments performed by undergraduate Ernest Marsden under the direction of Rutherford and German physicist Hans Geiger in 1909. A radioactive source emitting alpha particles (i.e., positively charged particles, identical to the helium atom nucleus and ...
In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, ... The alpha particle scattering experiment.
This model was discarded in 1911 on both theoretical and experimental due to the Rutherford's atomic model. Now let's understand Rutherford scattering experiment step by step. Rutherford's Alpha Particle Scattering Experiment. In this experiment, Ernest Rutherford bombarded a beam of alpha particles with a very thin gold foil.
The goal of each atomic model was to accurately represent all of the experimental evidence about atoms in the simplest way possible. Following the discovery of the electron, J.J. Thomson developed what became known as the "plum pudding" model (Figure \(\PageIndex{1}\)) in 1904. Plum pudding is an English dessert similar to a blueberry muffin.
Alpha Scattering. In 1909 a group of scientists were investigating the Plum Pudding model. Physicist, Ernest Rutherford was instructing two of his students, Hans Geiger and Ernest Marsden to carry out the experiment They were directing a beam of alpha particles (He 2+ ions) at a thin gold foil; They expected the alpha particles to travel through the gold foil, and maybe change direction a ...
on the structure of the atom and devise a new "nuclear atom" model. His predictions concerning the characteristics of this nuclear atom were confirmed by the subsequent experiments of Geiger and Marsden with the scattering of alpha particles by thin gold and silver foils (Phil. Mag. 25. 605 (1913), Figure 1).
Simulate Rutherford's experiment to understand atomic structure by observing alpha particles bouncing off atoms and determining they must have a small core.
The scattering foil is an annulus located coaxially with the α-source and detector with inner and outer diameters, 46.0 and 56.7 mm respectively. The angle βis determined by a fixed distance from source to scattering foil. The scattering angle θis varied by changing the distance from the scattering plane to the plane of the detector.