The History Of The Atom Part 5

Niels Bohr, Werner Heisenberg, Erwin Schrödinger

By Matthew Kelly 13B

Niels Bohr


Niels Bohr (7 October 1885 – 18 November 1962) was a Danish physicist who helped discover quantum physics and the structure of the atom.

The Rutherford–Bohr model or just Bohr model for short (1913) followed on from the plum-pudding model (1904) and the Rutherford model (1911).

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The Bohr model, introduced by Niels Bohr in 1913, shows the atom as small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity.


Werner Heisenberg


Werner Karl Heisenberg (December 5, 1901 – February 1, 1976) was a German physicist, Nobel Prize winner and one of the people who started a new area of physics called quantum mechanics. Most people think that he is one of the most important scientists of the 20th century. He is also well known for discovering the Heisenberg uncertainty principle, which explains that there is a limit on how well some things can be measured.

Heisenberg’s uncertainty principle is one of the most important results of twentieth century physics. It relates to measurements of sub-atomic particles. Certain pairs of measurements such as:

1. Where a particle is

2. Where it is going (its position and momentum) cannot be exactly found.

In other words you can know the position or the speed of the sub-atomic particle but you can’t know both.

Erwin Rudolf Schrödinger


Erwin Rudolf Josef Alexander Schrödinger was an Austrian Physicist. He was one of the founders of quantum mechanics and won the Nobel Prize in Physics in 1933.

The Schrödinger equation is a mathematical formula that forms the basis of quantum mechanics, the most accurate theory of how subatomic particles behave. It is a mathematical equation that was thought of by Erwin Schrödinger in 1925. It defines something called the wave function of a particle or system (group of particles) which has a certain value at every point in space for every given time. These values have no physical meaning, yet the wave function contains all information that can be known about a particle or system. We can therefore think of the various parts of the atom, especially electrons, as waves.


The electron waves for the first three Bohr orbits are visualized above, depicting the waves as meeting a kind of resonance condition so that the continuing waves interfere constructively with each under these conditions. The numbers apply to the hydrogen orbits.

The Bohr model of the atom started the progress toward a modern theory of the atom with its postulate that angular momentum is quantized, giving only specific allowed energies. Then the development of the quantum theory and the Schrodinger equation refined the picture of the energy levels of atomic electrons.

The model of the atom that therefore existed at the onset of the Second World War is of a nucleus surrounded by a cloud of electrons. It is a visual model that maps the possible locations of electrons in an atom. The model is used to describe the probable locations of electrons around the atomic nucleus. The electron cloud is also defined as the region where an electron forms a three-dimensional standing wave, the one that does not move relative to the atomic nucleus. The model does not depict electrons as particles moving around the nucleus in a fixed orbit. Based on quantum mechanics, it gives the probable location of electrons represented by an ‘electron cloud’.


The electron cloud model uses the concept of ‘orbitals’, referring to regions in the extra-nuclear space of an atom where electrons are likely to be found. An orbital is a mathematical function that describes the wave-like behaviour of electrons in an atom. With the help of this function, the probability of finding an electron in a given region is calculated. The term ‘orbital’ can be used to refer to the physical region where electrons can be found. They are designated with the names s, p, d, and f. The s orbitals are spherical, p orbitals re dumbbell-shaped, d orbitals have two angular nodes, and f orbitals have three. An orbital can contain no more than two electrons.

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