What is the atomic number?

Atomic number

The atomic number is defined as the number of protons that exist in the nucleus of an atom. This concept was historically important because it provided a theoretical basis for the realization of the periodic table of the elements . Dmitri Mendeleev’s discovery of the periodic law in the late 1860s was a remarkable achievement for the entire world as it provided a key organizing concept for the chemical sciences.. A problem that remained in Mendeleev’s final analysis was the inversion of certain elements in his periodic table, however, his contribution was of utmost importance to humanity and the scientific world.

Atomic numberWhat is the atomic number?

The atomic number is a concept that belongs to the field of physics and chemistry and that is closely related to the structure that an atom has and the total number of protons that the nucleus has.

The organization of the periodic table by means of an atomic number also solved some of the remaining problems of Mendeleev’s original work . For example, elements that appeared to be out of place when ordered according to their atomic weights appeared in their correct order when ordered according to their atomic numbers.

  • History of the atomic number
  • What is the atomic number
  • Represents
  • How to calculate the atomic number
  • Examples

History of the atomic number

The solution to this problem did not appear for almost half a century. Then the solution was born from X-ray research , which was discovered in 1895 by Wilhelm Röntgen . In his discovery he found a new form of electromagnetic radiation that had inspired a number of new research projects aimed at learning more about X-rays themselves and their effects on matter.

Charles Grover Barkla , a physicist at the Universities of London and Cambridge, started a line of X-ray research. Starting in 1903, he analyzed the way in which X-rays were scattered by gases, in general , and by elements, in particular. He found that the higher an element was on the periodic table, the more penetrating the rays it produced. He concluded that the X- ray pattern he observed for an element was associated with the number of electrons in the atoms of that element.

In 1913, Moseley discovered that the X-ray spectra of the elements changed in a simple and regular way as one moved up the periodic table and attributed this change to the number of electrons in the atoms of each element and therefore to the total positive charge in the nucleus of each atom.

Moseley’s discovery was an important contribution to the understanding of Mendeleev’s periodic law and provided a theoretical basis for the law. He showed that chemical properties were related to the number of electrons and nuclear charge in a regular and predictable way.

What is the atomic number

The identity that an atom has and its properties are given by the number of particles it contains. What makes chemical elements different from others is the quantity or number of protons that their atoms have within the nucleus . This number is known by the name of atomic number and is represented with the letter Z . It is located in the subscript to the left of the symbol of the corresponding element.


The atomic number of an element is responsible for representing the total number of protons found in an atom and is essential to understand the order in which the chemical elements that are within the periodic table of elements are found. . They also represent the order, starting with hydrogen as the first element because its atomic number is 1 and ununoctium being the last element that appears at the end of it with the atomic number of 118.

How to calculate the atomic number

The steps to follow in order to calculate the atomic number of an element are the following:

  • We must first look for a periodic table and observe that each element has different numbers.
  • Search for the element to be studied by name or by chemical symbol.
  • We will then look for the atomic number that is in the upper corner on the left side of the element. This number will always be a whole number .
  • You will need to confirm that nearby elements have a continuation in terms of their atomic number.
  • Then, the number of neutrons and the atomic weight must be found by applying the formula A – Z = n


  • Helium : its atomic number is 2.
  • Chlorine : the 17.
  • Fluorine : the number 9.
  • Lithium : corresponds to the number 3.
  • Chromium : 24.
  • Barium : 56.
  • Tantalum : its atomic number is 73.
  • Astato : number 85.

Related Articles

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top button