Rutherford Atomic Model
Rutherford who was a student of J. J. Thomson discovered Nucleus which contained protons and neutrons inside it. This discovery made huge changes to the atomic structure. The observations made by Thomson in his experiment were used by Rutherford to propose his theory for atomic structure through an experiment called Rutherford’s Alpha Ray Scattering Experiment.
Alpha Ray Scattering Experiment
Rutherford used the radioactivity phenomenon in conducting his experiment. He used the radioactive material radium bromide (RaBr). RaBr emits α particles which is a form of radiation. A thin gold metal sheet was put up in the setup. Then the alpha ‘α’ particles were bombarded on this sheet. The α particle has a charge of +2. To observe the deflection of the particles a screen of Zinc Sulfide (ZnS) was used and placed behind the Gold foil. Rutherford further developed a detector in order to count the number of radioactive particles. Initially, he recorded the count rate of RaBr as he kept a count of α particles emitted per minute.
Observation of Alpha Ray Scattering Experiment
Following observations were made by Rutherford and conclusions were drawn:
- Most of the α particles passed through thin sheets. This means most of the atom’s space is empty.
- Another observation made was that some of the α particles deflected a bit in every direction. This leads to the conclusion that the positive charge is not distributed uniformly throughout the atom.
- Very few α particles get deflected back along the path that they were traveling on. This happened because of charges repelling each other. Seeing this Rutherford concluded that the positive charge in an atom exists in a very small volume.
- Not only the positively charged particles but a lot of mass is also concentrated in a very small volume. Rutherford named this region as Nucleus.
- Rutherford also came up with the argument that electrons are present in orbits around the orbits, much like the planets in the solar system. Electrons are negatively charged and they revolve around the nucleus.
- The electrons and nucleus are held by the electrostatic force of attraction because they are negatively and positively charged respectively.
Conclusion of Rutherford’s model
Drawing conclusions from all the above observations, Rutherford proposed his Atomic structure which had the following properties –
- The nucleus lies at the center of the atom, and the maximum of the charge and mass is concentrated there only.
- Atoms are spherical in nature.
- Electrons revolve around the nucleus in a circular orbit.
Discovery of Nucleus
In Gold Foil Alpha Particle Experiment, Rutherford observed that most of the spaces inside an atom are vacant and there is a small dense region located at the center inside the atom. He termed this region as Nucleus and said that this Nucleus is positively charged and most of the masses of the atom are concentrated in Nucleus only.
Limitations of Rutherford Atomic Model
Just like other atomic models, Rutherford’s model also had many shortcomings.
- Since electrons revolve in a circular orbit around the nucleus in an atom it is an accelerated motion. As per Electromagnetic Theory when a charged particle is in accelerated motion it loses energy. Hence, electrons will spend a lot of energy and eventually, they will lose the entire energy and the atom will collapse. This raises serious questions about the stability of the atom.
- Rutherford didn’t say anything about the position of electrons whether all electrons be in the same or different orbits and the reason behind it.
- If the electrons are revolving continuously around the nucleus, then the spectrum that they emit should be a continuous spectrum, but what we observe is a line spectrum.
Atomic Structure
Atomic structure is the structure of an atom that consists of a nucleus at the center containing neutrons and protons, while electrons revolve around the nucleus. Atoms are made up of a very tiny, positively charged nucleus that is surrounded by a cloud of negatively charged electrons.
The earliest concept of atoms was given by Indian philosopher Maharshi Kanad who proposed that matter is made up of microscopic indestructible particles called ‘Parmanu’. A Greek philosopher named Democritus also initially claimed that matter is formed of atoms, and is credited with developing the concepts of atomic structure and quantum mechanics. Later in the 1800s, John Dalton a British Scientist put out the first atomic structure scientific theory.
This article explores the concept of atomic structure in detail, including the atomic models, and the concept of quantum theory.
Table of Content
- What is Atomic Structure?
- Atomic Models
- Dalton’s Atomic Theory
- Postulates of Dalton’s Atomic Theory
- Demerits of Dalton’s Atomic Theory
- Thomson’s Atomic Model
- Cathode Ray Experiment
- Observations of Cathode Ray Experiment
- Discovery of Electron
- Plum Pudding Model
- Drawbacks of Thomson’s Atomic Model
- Rutherford Atomic Model
- Alpha Ray Scattering Experiment
- Observation of Alpha Ray Scattering Experiment
- Conclusion of Rutherford’s model
- Discovery of Nucleus
- Limitations of Rutherford Atomic Model
- Bohr’s Atomic Model
- Postulates of Bohr’s Atomic Theory
- Limitations of Bohr’s Atomic Theory
- Quantum Mechanical Model of Atom
- Dual Behaviour of Matter
- Heisenberg Uncertainty Principle
- Schrodinger Wave Equation
- Postulates of Quantum Mechanical Model of Atom
- Quantum Number
- Principal Quantum Number(n)
- Azimuthal Quantum Number(l)
- Magnetic Quantum Number(ml)
- Spin Quantum Number(ms)
- Subatomic Particles
- Isotopes
- Atomic Structure of Isotopes
- Electronic Configuration of Elements
- Aufbau Principle
- Hund’s Rule
- Pauli Exclusion Principle
- Atomic Structure Class 11
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