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Electron Cloud Model

Electron Cloud Model

What is an electron cloud model? Who proposed the concept of an electron cloud? Read on to find out.
Manali Oak
Last Updated: Jan 27, 2018
Quick Read
Erwin Schrodinger, an Austrian physicist came up with the electron cloud model in 1926. The electron cloud refers to a region outside the nucleus where an electron is most likely to be found.
Before understanding what an electron cloud model is, it is important to know about the forces that bind the electrons together. You might also like to know about the parts of an atom before exploring the concept of an electron cloud.
What binds the subatomic particles in an atom together?
It's an electromagnetic force; a force of attraction that exists between the electrons and the nuclear protons, and binds them to the atom. The attractive force of an electron is directly proportional to its distance from the atomic nucleus. Hence the energy required to separate an electron from the atom varies inversely with its distance from the nucleus.
Where in the atom are electrons found?
Electrons orbit around the nucleus of an atom. Each orbital is equivalent to an energy level of the electron. On absorbing a photon, an electron moves to a new quantum state by acquiring a higher level of energy. On similar lines, an electron can fall to a lower energy level by emitting a photon, thus radiating energy.
What is an electron cloud model?
Electron cloud model
The model provides the means of visualizing the position of electrons in an atom. 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 behavior 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 not more than two electrons.
Who came up with the electron cloud model?
The term, 'electron cloud' was used by the Noble Prize winner Richard Feynman, an American physicist, in The Feynman Lectures on Physics.

The efforts of notable scientists like Ernest Rutherford, Niels Bohr, Werner Heisenberg, and others led to the formation of a model that could be used to estimate the positions of electrons in an atom.

J.J. Thomson, a British physicist was working on cathode rays. His work led to the discovery of electrons in 1897. Till that time, atoms were believed to be the indivisible units of matter. His revolutionary discovery proved the conventional theory wrong.

In 1909, Rutherford brought out the fact that the positive charge and the mass of an atom is concentrated towards its center, and that electrons orbit around the atomic center.

Niels Bohr, a Danish physicist modified Rutherford's model by proposing that the orbital of electrons is restricted to predefined orbits, and that they can make transitions between orbits, on absorbing or emitting energy.

Schrodinger built on his idea and came up with an electron cloud model. It consisted of a nucleus surrounded by clouds of electrons. The clouds indicate the probable positions of electrons in an atom. Greater density of electrons in a certain area is indicative of a higher probability of finding electrons in that atomic region.

Werner Heisenberg, best known for his uncertainty principle, which states that it is not possible to obtain precise values of both position and momentum of a particle at the same time, further added to the idea of the electron cloud model. He suggested that one could only find the probable location of an electron is a certain volume. He determined that the only way to describe the location of an electron in an atom is through probability distribution. This principle forms the basis of the electron cloud model.
Thus we see that an electron cloud model is a visual model that gives the probable locations of electrons in an atom. In this model, electrons are not shown as particles moving around the nucleus in a fixed orbit. It is a modern and the most accepted atomic model, and has rendered all previous explanations of the atomic structure obsolete.