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The atomic orbital model, also known as the Schrödinger model, was introduced by Erwin Schrödinger which suggested that electrons did not actually move in distinct orbits but in a wave-like behaviour as the exact location of an electron in an orbit cannot be precisely calculated. Each layer of shell contains a number of sub shells which correspond to the shell number. They can further be divided into orbits, with a specific area of space which can contain up to a maximum of 2 electrons. This, however, is not the actual representation of the actual atomic structure but allows us to grasp the concept more easily.

Atomic Orbital Model

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References

Evolution of the Atomic

Model

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• Representation of different types of vibrations which form the shape of atomic orbitals

Thomson’s model of the atom is depicted rather like raisin bread, and thus is sometimes called the raisin bread model. He assumed that the basic body of an atom is a spherical object containing N electrons confined in homogeneous jellylike but relatively massive positive charge distribution whose total charge cancels that of the N electrons. An experiment was carried out in which the alpha rays were collided against a thin metal foil. Their results showed that almost all incident alpha particles penetrate the foil and go straight in forward direction but a few are scattered in very large angles. The results of the alpha particle scattering cannot be explained by Thomson's atomic model. Thomson's raisin bread model (plum pudding model) therefore cannot be valid as an atomic model.

Thomson’s Atomic Model Early theories and basic models

Rutherford & Bohr’s Model

Unbreakable small solid “balls”

Greek Theory The word “Atom” originated from a Greek word “atomos” meaning the smallest unit of matter, though there are smaller units of matter than atoms like protons and neutrons. Leucippus and Democritus, two Greek philosophers of the 5th century BC, believed that the atom was irreducible and indestructible. They believed that everything in the universe was composed of atoms. Atoms differed as to their size, shape, weight, electric configuration, or atomic and mass numbers. Democtritus' model consists of an invisible small sphere. It contained no subatomic particles like protons or neutrons. He drew his model to show that all atoms are indestructible and unchangeable. He assumed that they differed in shape and temperature too. Dalton’s Atomic Model Following the Greeks' beliefs was John Dalton's model. Dalton is considered the Father of modern atomic theory, and for many years the unit for atomic weight is called "Dalton". Dalton, like the Greek philosophers before him, viewed atoms as unbreakable small solid balls with no presence of subatomic particles, but he did not expose much about the atoms' structure and outline. In the late 19th Century, other scientists found evidence that atoms are not small solid balls and can be broken. Dalton's atom model needed to be improved to satisfy the new findings.

Positively charged matter

Electrons

Rutherford’s atomic model Rutherford thought that the atom consisted of a black big ball at the center which was the nucleus and small red points moving around the nucleus which were the electrons. Rutherford's new model for the atom, based on the experimental results, had the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and containing the bulk of the atomic mass, like that of the solar system. After Rutherford's discovery, scientists started to realize that the atom is not ultimately a single particle, but is made up of far smaller subatomic particles. Following research was done to figure out the exact atomic structure which led to Rutherford’s gold foil experiment. Bohr Model The Bohr model, which Niels Bohr came up with, showed that the atom was a positively charged nucleus surrounded by electrons which orbited the nucleus, with electrostatic forces acting as the attraction force between the nucleus and the electrons. It was a modification of past models, including the Rutherford model. The Bohr Model is also known as the Bohr-Rutherford model because it is a quantum physics-based modification of the original Rutherford model. The Rutherford model suggested that electrons could move anywhere within the volume of the space surrounding the nucleus. Contrary to the Rutherford model, the Bohr model imposed restrictions on the movement of electrons such that they could only orbit the nucleus.

Nucleus (consists of Protons and neutron s)

electrons

orbits

electrons

Nucleus (consists of proton and electrons)

orbits