Austrian-American physicist Wolfgang Pauli discovered that no two fermions can have the exact same quantum numbers. This principle is called the Pauli exclusion principle, which states that two or more identical electrons cannot occupy the same orbital in an atom.

In 1912, Bohr was working for the Nobel laureate J.J. Thompson in England when he was introduced to Ernest Rutherford, whose discovery of the nucleus and development of an atomic model had earned him a Nobel Prize in chemistry in 1908. Under Rutherford’s tutelage, Bohr began studying the properties of atoms.

Niels Bohr (1885-1962) was a Danish physicist and winner of the 1922 Nobel Prize in Physics. Bohr began his work on the Manhattan Project after fleeing to Sweden from Denmark because of German occupation in 1943.

Using Planck’s constant, Bohr obtained an accurate formula for the energy levels of the hydrogen atom. He postulated that the angular momentum of the electron is quantized–i.e., it can have only discrete values.

In 1913, Niels Bohr proposed a theory for the hydrogen atom, based on quantum theory that some physical quantities only take discrete values. Bohr’s model explained why atoms only emit light of fixed wavelengths, and later incorporated the theories on light quanta.

Bohr’s model explains the spectral lines of the hydrogen atomic emission spectrum. While the electron of the atom remains in the ground state, its energy is unchanged. When the atom absorbs one or more quanta of energy, the electron moves from the ground state orbit to an excited state orbit that is further away.

First, the Bohr model violates the Heisenberg Uncertainty Principle , since it states that electrons have a known radius and orbit. The Bohr Model also provides an incorrect value for the ground state orbital angular momentum and doesn’t work as well for creating diagrams of larger atoms.

The electron cloud model is the current quantum model of the atom. Up here on the board, you can basically just see how atomic models evolves with more discovery that scientists had to come to the model that Schrodinger came up with, which is the current quantum model of the atom.

Bohr Model

The electron cloud model is currently the most sophisticated and widely accepted model of the atom. It retains the concept of the nucleus from Bohr and Rutherford’s models, but introduces a different definition of the motion of electrons around the nucleus.

• Dalton model (Billiard ball model)
• Thomson model (Plum pudding model)
• Lewis model (Cubical atom model)
• Nagaoka model (Saturnian model)
• Rutherford model (Planetary model)
• Bohr model (Rutherford–Bohr model)
• Bohr–Sommerfeld model (Refined Bohr model)
• Gryziński model (Free-fall model)

Plum-pudding model (1904) Nuclear model (1911) Planetary model (1913) Quantum mechanical model (1926-present)

Thomson atomic model, earliest theoretical description of the inner structure of atoms, proposed about 1900 by William Thomson (Lord Kelvin) and strongly supported by Sir Joseph John Thomson, who had discovered (1897) the electron, a negatively charged part of every atom.

Ernest Rutherford’s most famous experiment is the gold foil experiment. A beam of alpha particles was aimed at a piece of gold foil. Most alpha particles passed through the foil, but a few were scattered backward. This showed that most of the atom is empty space surrounding a tiny nucleus.

Most important, he postulated the nuclear structure of the atom: experiments done in Rutherford’s laboratory showed that when alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most of the atomic mass.

The drawback of Rutherford model is: It can’t explain the stability of an atom. As per the model, the orbital revolution of electrons around the nucleus is not stable as the revolving electrons in orbits will undergo acceleration and emit energy.

‘ It was eventually discovered that this model does not accurately represent the behavior of electrons or the sizes of particles. The Rutherford model is one of the most popular models of the atom even though it was only considered accurate from 1909 to 1913.

Rutherford observed that when a beam of alpha particles (which are now known to be helium nuclei) struck a thin gold foil, some of the particles were deflected backward. This work led to Rutherford’s atomic model, in which a heavy nucleus of positive charge is surrounded by a cloud of light electrons.

Limitations of Rutherford Atomic Model Rutherford’s model was unable to explain the stability of an atom. According to Rutherford’s postulate, electrons revolve at a very high speed around a nucleus of an atom in a fixed orbit. However, Maxwell explained accelerated charged particles release electromagnetic radiations.

Rutherford’s model of atom was wrong because the presence of electrostatic attraction between the nucleus and the electrons. The electrons should fall into the nucleus, but they didn’t. Electrons do not move around the nucleus in circular orbits.

The Bohr Model is very limited in terms of size. Poor spectral predictions are obtained when larger atoms are in question. It cannot predict the relative intensities of spectral lines. It does not explain the Zeeman Effect, when the spectral line is split into several components in the presence of a magnetic field.

James Chadwick