Atom It is the smallest portion of any chemical element, which cannot be divided and which has an independent existence. Atoms are composed of electrons that orbit around a nucleus with neutrons and protons .

Atoms of different elements have different amounts of protons . He atomic number (which is identified with the letter Z , for the German term zahl) indicates the amount of protons that is present in the nucleus of an atom. East number , therefore, is responsible for defining the electronic configuration of the atom and allows the ordering of the various chemical elements in the periodic table , which begins with hydrogen (Z = 1) and continues with helium, lithium, beryllium, boron, carbon and nitrogen.

We also have to add that the number of protons that exist in the nucleus of a particular atom is equal to the number of electrons that surround it in what is called the cortex.

The list of chemical elements established based on their atomic number can be determined to be headed by these ten elements: with 1 the hydrogen, with the number 2 helium, 3 is for lithium, 4 is beryllium, 5 is boron boron, 6 is carbon, 7 is nitrogen, 8 is oxygen, 9 is fluorine and 10 is neon.

To this we can also add that in total this list is formed by a total of 115 chemical elements, the last one being the ununoctio. Presumably this is a colorless noble gas whose temporary symbol is the following: Uuo.

It is important to keep in mind that an unaltered atom is electrically neutral : This means that your atomic number will always be the same as your number of electrons.

Although the periodic table of the elements is usually attributed to Dimitri Mendeleev (responsible for ordering the elements according to the variations of the chemical properties), who specified the organization according to the physical properties of the atoms was Julius Lothar Meyer .

However, the important role of English physicist and chemist Henry Moseley who established his own law of atomic numbers, called Moseley's Law, cannot be ignored. In 1913, it was announced that it established that there was a clear systematic relationship between the wavelength of the X-rays that were emitted by the atoms and their atomic number.

In this way, with this discovery, this British chemist came to oppose or to counter the proposals that the mentioned Mendeleev made four decades earlier.

We have already said that the number of protons (expressed by the atomic number) is equal to the number of electrons. He mass number (TO ), on the other hand, indicates the number of particles that an atom has in its nucleus. Therefore, it expresses the sum of protons and neutrons. It is possible to establish, in short, the following relationship between the atomic number and the mass number: A = Z + N , where N equals the number of neutrons.