atomic models

Chemistry

2022

We explain what atomic models are and how they have evolved, from ancient times to modern times.

These models seek to basically explain what matter is made of.

What are atomic models?

Atomic models are known as the different graphic representations of the structure and operation of the atoms. Atomic models have been developed throughout the history of humanity from the ideas that in each era were handled regarding the composition of the matter.

The first atomic models date back to classical antiquity, when philosophers and naturalists ventured to think and deduce the composition of things that exist, that is, of matter.

Atomic model of Democritus (450 BC)

The "Atomic Theory of the Universe" was created by the Greek philosopher Democritus together with his mentor, Leucippus. At that time the knowledge were not achieved through experimentation, but through the reasoning logical, based on the formulation and discussion of ideas.

Democritus proposed that the world was made up of very small and indivisible particles, of existence eternal, homogeneous and incompressible, whose only differences were in shape and size, never in internal functioning. Are particles they were baptized as "atoms", a word that comes from the Greek atémnein y means "indivisible".

According to Democritus, properties of matter they were determined by the way the atoms were grouped together. Later philosophers such as Epicurus added to the theory the movement random of atoms.

Dalton's atomic model (1803 AD)

The first atomic model with scientific bases was born within the chemistry, proposed by John Dalton in his "Atomic Postulates". He maintained that everything was made of atoms, indivisible and indestructible, even by means of chemical reactions.

Dalton proposed that the atoms of the same chemical element were equal to each other and had the same mass and equal properties. On the other hand, he proposed the concept of relative atomic weight (the weight of each element with respect to the weight of hydrogen), comparing the masses of each element with the mass of hydrogen. He also proposed that atoms can combine with each other to form chemical compounds.

Dalton's theory had some flaws. He claimed that chemical compounds were formed using the fewest possible atoms of their elements. For example, the molecule of WaterAccording to Dalton, it would be HO and not H2O, which is the correct formula. On the other hand, he said that the elements in gaseous state They were always monatomic (made up of a single atom), what we know is not real.

Lewis's atomic model (1902 AD)

Also called "Model of the Cubic Atom", in this Lewis model proposed the structure of the atoms distributed in the form of a cube, in whose eight vertices were the electrons. This allowed progress in the study of the valences atomic and chemical links, especially after its update by Irving Langmuir in 1919, where he raised the "atom of the cubic octet".

These studies were the basis of what is known today as the Lewis diagram, a very useful tool to explain covalent bonding.

Thomson's Atomic Model (1904 AD)

Thomson assumed that atoms were spherical with electrons embedded in them.

Proposed by J. J. Thomson, discoverer of the electron in 1897, this model is prior to the discovery of the protons Y neutrons, so he assumed that atoms were made up of a positively charged sphere and negatively charged electrons were embedded in it, like raisins in pudding. Bliss metaphor He gave the model the epithet "Raisin Pudding Model."

This model made an incorrect prediction of the positive charge on the atom, since it stated that it was distributed throughout the atom. Later this was corrected in Rutherford's model where the atomic nucleus was defined.

Rutherford's atomic model (1911 AD)

Ernest Rutherford made a series of experiments in 1911 from gold leaf. In these experiments he determined that the atom is composed of a positively charged atomic nucleus (where most of its mass is concentrated) and electrons, which freely rotate around this nucleus. In this model the existence of the atomic nucleus is proposed for the first time.

Bohr's atomic model (1913 AD)

When jumping from one orbit to another, the electrons emit a photon differentiating the energy between orbits.

This model begins in the world of physical to quantum postulates, so it is considered a transition between classical mechanics and quantum. Danish physicist Niels Bohr proposed this model to explain how electrons could have stable orbits (or stable energy levels) surrounding the nucleus. It also explains why atoms have characteristic emission spectra.

In the spectra carried out for many atoms, it was observed that electrons of the same energy level had different energies. This showed that there were errors in the model and that there must be energy sublevels at each energy level.

Bohr's model is summarized in three postulates:

  • Electrons trace circular orbits around the nucleus without irradiating Energy.
  • The orbits allowed for electrons are those with a certain value of angular momentum (L) (amount of rotation of an object) that is an integer multiple of the value, where h = 6.6260664 × 10-34 and n = 1, 2, 3….
  • Electrons emit or absorb energy when jumping from one orbit to another and in doing so they emit a photon that represents the difference in energy between the two orbits.

Sommerfeld's atomic model (1916 AD)

Sommerfeld's model was based in part on the relativistic postulates of Albert Einstein.

This model was proposed by Arnold Sommerfield to try to cover the deficiencies of the Bohr model.

It was based in part on the relativistic postulates of Albert Einstein. Among its modifications is the assertion that the orbits of the electrons were circular or elliptical, that the electrons had electric flow lowercase and that from the second energy level there were two or more sublevels.

Schrödinger's atomic model (1926 AD)

Proposed by Erwin Schrödinger from the studies of Bohr and Sommerfeld, he conceived electrons as undulations of matter, which allowed the subsequent formulation of a probabilistic interpretation of the wave function (a magnitude that serves to describe the probability finding a particle in space) by Max Born.

That means that you can study probabilistically the position of an electron or its quantity of movement but not both at the same time, due to the Heisenberg Uncertainty Principle.

This is the atomic model in force at the beginning of the XXI century, with some later additions. It is known as the "Quantum-Undulatory Model".

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