We explain what atomic models are and how they have evolved, from Antiquity to the current times.
What are atomic models?
Atomic models are known as the different mental representations of the structure and functioning of atoms , developed throughout the history of mankind, based on the ideas that were handled in each era regarding what the matter was made of.
The first atomic models date from classical antiquity , when philosophers and naturalists struggled to think and deduce the composition of things that exist, and the most recent (and currently considered as valid) were developed in the twentieth century, when nuclear bombs and: the first real advances in atomic manipulation were nuclear plants of power.
Atomic model of Democritus (450 BC)
The “Atomic Theory of the Universe” was created by the Greek philosopher Democritus and his mentor, Leucipo. At that time, knowledge was not achieved through experimentation, but logical reasoning, based on the formulation of ideas and their debate.
Democritus proposed that the world was made up of minimal and indivisible particles , of eternal existence, homogeneous and incompressible, whose only differences were in shape and size, never of internal functioning. These particles were baptized as atoms, a word that comes from the Greek ἄτομοι and means “indivisible”.
According to Democritus, the properties of matter were determined by the way atoms were grouped. Later philosophers like Epicurus added to the theory the random movement of atoms.
Dalton atomic model (1803 AD)
The first atomic model with scientific bases was born in chemistry , proposed by John Dalton in his “Atomic Postulates.” He argued that everything was made of atoms, indivisible and indestructible , even by chemical reactions. The known elements depended on their atoms , which possessed the same charge and identical properties, but a different relative atomic weight : this because, compared to hydrogen, they showed different masses.
Dalton deduced that atoms are grouped keeping different proportions and thus chemical compounds are formed.
Lewis atomic model (1902 AD)
Also called the Cubic Atomic Model, it proposed the structure of atoms as a cube , in whose eight vertices were electrons . It was proposed by Gilbert N. Lewis and allowed progress in the study of atomic valences and molecular junctions, especially after its update by Irving Langmuir in 1919, thus developing the “atom of the cubic octet”.
These studies gave rise to what is now known as the Lewis diagram, from which the covalent atomic bond is known.
Thomson’s atomic model (1904 AD)
Proposed by JJ Thomson, discoverer of the electron in 1897, this model is prior to the discovery of protons and neutrons, so he assumed that atoms consisted of a sphere of positive charge and different electrons of negative charge embedded in it, such as raisins in the pudding This metaphor gave the model the epithet of “Raisin Pudding Model”.
Rutherford atomic model (1911 AD)
Ernest Rutherford carried out a series of experiments in 1911 from gold plates and other elements, thanks to which he determined the existence of a positively charged atomic nucleus in which the highest percentage of its mass was found . The electrons, on the other hand, revolved freely around said nucleus or center.
Atomic model of Bohr (1913 AD)
This model begins quantum postulates in the world of physics , so it is considered a transition between classical and quantum mechanics . The Danish physicist Niels Bohr proposed it to explain how electrons could have stable orbits surrounding the nucleus , and other details that the previous model could not account for.
This model is summarized in three postulates:
- The electrons draw circular orbits around the nucleus without radiating energy.
- The orbits allowed to the electrons are calculable according to their angular momentum (L).
- Electrons emit or absorb energy when jumping from one orbit to another and in doing so emits a photon that represents the difference in energy between both orbits.
Atomic model of Sommerfeld (1916 AD)
It was proposed by Arnold Sommerfield to try to fill the potholes presented by the Bohr model from the relativistic postulates of Albert Einstein. Among its modifications are that the orbits of the electrons were circular or elliptical , that the electrons had tiny electrical currents and that from the second energy level there were two or more sub-levels.
Atomic model of Schrödinger (1926 AD)
Proposed by Erwin Schrödinger from the Bohr and Sommerfeld studies, he conceived electrons as undulations of matter , which allowed the subsequent formulation of a probabilistic interpretation of the wave function, by Max Born.
That means that the position of an electron or its amount of movement can be studied probabilistically , but not both at the same time, due to Heisenberg’s famous Uncertainty Principle.
This is the atomic model in force at the beginning of the 21st century, with some subsequent additions. It is known as quantum-wave model.