INTRODUCTION OF RUTHERFORD MODEL
Ancient Indian philosopher Kanada said that matter is made up of tiny particles. The Greek philosopher Democritus and many others said that matter is made up of discrete particles and that these particles are indivisible. In Greek the word ‘atom’ means indivisible. That is why these smallest particles of matter are called atoms. But all this at that time was imaginary. In the early 19th century, scientist John Dalton published a theory to explain chemical bonding. That theory is known as Dalton’s atomic theory. According to this theory matter is made up of numerous indivisible atoms.
In the last decade of the 19th century, scientists such as William Crooks, John Joseph Thomson, Philip Lennard paved the way for the discovery of electrons by experimenting with electromagnetism in gases under very low pressure. Among them, Thomson is considered as the discoverer of the electron. Then the misconception that ‘atoms are indivisible’ came to an end.
RUTHERFORD MODEL
We know that the structure of an atom consists of electrons, protons, and neutrons. This was appropriately portrayed after multiple scientists proposed several models. Ernest Rutherford proposed the Rutherford atomic model, sometimes known as the Rutherford model of the atom. However, it is no longer considered the most accurate representation of an atom.
ALPHA PARTICLE'S SCATTERING EXPERIMENT
Rutherford and his fellow scientists completed this famous experiment in 1911. Alpha particles emitted from a radioactive source are equipotential. These particles are made into parallel currents and deposited on a very thin sheet of any heavy metal such as gold, silver etc. The atomic number Z of these metals is very high; Z = 79 for gold and Z = 47 for silver. It is also possible to beat these metals into very thin sheets, about 10-7 m thick. Because the thickness is so small, it can be assumed that each α particle collides or interacts with only one atom in the interlayer. After passing through the sheet, the α particles are detected by a fluorescence screen for different diffraction angles Ɵ.
Some α particles may return to their previous region due to deflection without crossing the sheet again; In that case the value of Ɵ is greater than 90°.
OBSERVATION & INFERENCE
- Most of the α particles cross the metal sheet almost straight and exit in the opposite direction. From this it can be concluded that most of the space in the atom is empty.
- A very small number of α particles are deflected; In this case Ɵ ≈ 1°, that is, the value of the deflection angle is 1° or close to it. This is called low angle scattering. This phenomenon can be assumed to be the result of Coulombic attraction between a α particle and an atomic electron. Each α particle has a charge of +2e and each electron has a charge of -e; As a result, a constant-current coulombic force of attraction acts between them. However, since the mass of an α particle is about 7000 times the mass of an electron, even this attractive force causes very little deflection of the α particle. From this it can be concluded that electrons are isolated in atoms.
- A very small number of α particles are scattered over a much larger angle. Even, the value of the deflection angle Ɵ may be greater than 90°, the α particle returns to the exact opposite direction i.e. Ɵ = 180°. This is called large angle scattering. Quantitatively analyzing the very small number of such perturbations, Rutherford concluded that the entire positive charge and almost the entire mass of the atom is concentrated in a very short range; It is called the nucleus of the atom. A α particle has charge of +2e and charge of nucleus +Ze; As a result, there is a strong electrostatic repulsive force between them—the force that causes deflection at high angles. Quantitative analysis also concluded that the diameter of the nucleus of an atom is about 10-14 m, which is only about 10,000th of the diameter of the entire atom (about 10-10 m). Hence their volume ratio is about 1 : 10¹².
A complete atom consists of a large area of empty space, a large number of negatively charged electrons spaced apart, and a densely packed nucleus of high mass and positive charge—a combination Rutherford compares to the solar system. Even in the solar system, most of the region is empty space, the planets are isolated from each other and most of the mass of the solar system is concentrated within a very short range of the sun. The difference is: the gravitational force acts as the force of attraction between the Sun and the planets; The static coulombic force of attraction acts as the force of attraction between the nucleus and electrons of an atom.
Rutherford’s ideas about the structure of atoms through the above observations and analysis are known as Rutherford model or Rutherford model.
The key to this model is: At the center of every atom is a nucleus; Electrons revolve around the nucleus in various circular orbits. The static-electric force of attraction acting between the positive charge of the nucleus and the negative charge of each electron provides the centripetal force necessary to orbit the electron.
The key to this model is: At the center of every atom is a nucleus; Electrons revolve around the nucleus in various circular orbits. The static-electric force of attraction acting between the positive charge of the nucleus and the negative charge of each electron provides the centripetal force necessary to orbit the electron.
DRAWBACKS OF RUTHERFORD MODEL
(I) Instability of atom: Each rotating electron in an atom has a centripetal acceleration. According to Maxwell’s theory of electromagnetic waves in classical physics, electromagnetic radiation is emitted when a charged particle is accelerated. So, this radiation is also supposed to occur from the negative electrons of the atom and the energy of the electrons is converted into radiation energy. If this actually happened, the electrons would lose energy and fall on the nucleus due to static attraction. Theoretical calculations show that the lifetime of an atom would not exceed 10-8 s. But the permanence of matter and substance proves that atoms are not impermanent.
(II) Atomic Spectrum: If the energy of the electron is continuously converted to the energy of the radiation, a continuous spectrum should be obtained from the atom. But the atomic spectrum of elements like hydrogen, helium etc. is a line spectrum and not a continuous spectrum.
Pingback: Nucleus - ASTRONOMY ADVENTURE
Good
♥️♥️
Pingback: What is Nuclear Fission: A Detailed Overview About it!!
Pingback: Bohr's Model - ASTRONOMY ADVENTURE