Definition of Atomic Model

The knowledge of the atom is possible thanks to an explanatory model, known as the atomic model. It is a representation graph or symbolic of the atom that allows to understand the structure of all the particles that compose it.

Different explanations about atoms throughout history

The first reference to the atom took place in ancient Greece and it was the philosopher Democritus who affirmed that the atom is the particle of the smallest possible matter and is indivisible and indestructible. His ideas were the result of intellectual intuition and not experimentation.

In the nineteenth century, the British scientist John Dalton explained a series of previously unknown laws that are considered the first step in modern atomic theory. Dalton explained the law on conservation of mass, the law of constant composition and the law of multiple proportions. Dalton imagined that the atoms were like compact spheres and with different sizes and masses.

At the beginning of the 20th century, the Englishman Joseph Thompson experimented with cathode rays and concluded that there were negative particles inside the atom and he called these particles electrons. This made him

think that there had to be some positive parts to counteract the negative charges of the electron and for this reason his model views the atom as a sphere of positive matter surrounding negative matter. With Thompson's contribution, the atom was conceived as a divisible particle and, on the other hand, he was the one who found the relationship between mass and electric charge of the atom.

Current atomic model

Atoms are not visible and therefore a theory or model is necessary to understand how they work.

Currently it is accepted that the atom is made up of two parts: the nucleus that is in the center and the periphery where the electrons are.

The nucleus is made up of protons that have a given mass and a positive charge and, on the other hand, by neutrons, which have a mass similar to that of the proton but an electric charge of zero (for this reason they are called neutrons).

At the periphery of the atom are the electrons, which have a certain mass and an electric charge equal to that of the proton but negative. This structure of the atom is the basis of current atomic theory. To express its representation the atom is accompanied by its atomic mass and its atomic number (the concept of atomic number represents the number of protons in the nucleus atomic and the concept of atomic mass represents the number of protons plus the number of neutrons in the core).

Photos: Fotolia - Sergey Nivens / Sergey Nivens

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