From the Latin atŏmum, an atom is the smallest quantity of a chemical element that has its own existence and that is considered indivisible. The atom is made up of a nucleus with protons and neutrons and several orbital electrons, the number of which varies according to the chemical element.
However, in addition to the elements that compose it, it is important to emphasize that every atom has a series of properties that are essential to take into account when working with it. In this case, we find the fact that they are the size, the mass, the electrical interactions that are established between electrons and protons or the energy levels.
The atom is also called as the fundamental particle, thanks to its characteristic of not being able to be divided by chemical processes. From the 16th and 17th centuries, with the development of chemistry, atomic theory began to advance with certainties that, until then, were impossible to obtain.
Chemists managed to discover that any liquid, gas or solid could be decomposed into different elements or ultimate constituents (for example, each water molecule is made up of two hydrogen atoms and one oxygen atoms: H2O). John Dalton was the one who showed that atoms joined together according to certain definite proportions.
However, there have also been other authors who, in a profound and intense way, have left their mark on the study and analysis of atoms. This would be the case, for example, of the British scientist Joseph John Thomson. He went down in history not only as the inventor of the mass spectrometer but also as the discoverer of two fundamental elements: isotopes and the electron.
The New Zealand physicist Ernest Rutherford, the Danish Niels Bohr or the French Louis-Victor de Broglie are other scientists who, throughout history, have developed their own theories and atomic models with more or less success and acceptance by the scientific community.
In this case, it is important to underline the role of the last cited physicist, since in 1929 he won the Nobel Prize for having managed to discover the wave nature of what the electron is.
We said at the beginning of this definition that the atomic nucleus is made up of protons and neutrons. Protons have a positive energy charge, whereas neutrons have no charge. The difference between the different chemical elements is given by the number of protons and neutrons in their atoms. On the other hand, the number of protons contained in the nucleus of an atom is called the atomic number.
The periodic table of the elements is an organization that allows to distribute the different chemical elements according to certain characteristics and criteria. The simplest nucleus is that of hydrogen, which has a single proton. That is why it appears in the first place of the table. Hydrogen is followed by helium, which has two protons and two neutrons.
In addition to all the above, we cannot ignore the existence of a colloquial expression that uses the term at hand. It is the expression “in an atom” that comes to be synonymous with “in the smallest thing.”