Scientists and chemists have always sought ways of systematizing the elements in a way that would allow to represent their similar qualities. After long years of efforts, atomic number has become the main characteristic for elements systematizing and the modern periodic table was created. Historically, scientists were using atomic weights to structure elements even at times when the idea that atoms consists of smaller parties such as (protons, neutrons, electrons) had not been developed yet. Nevertheless, according to some sources, the basis of the modern periodic table had been well-established and even used to predict the properties of undiscovered elements long before the concept of the atomic number was developed (Royal Society of Chemistry, n.d.).
One of the first persons who tried to organize the elements in proper order was John Dalton in 1800s. For this purpose he created a system of elements (hydrogen , oxygen , nitrogen , carbon, sulfur , phosphorus), basing it on their atomic masses comparatively to hydrogen (which atomic mass was equal to 1). This work, however, is hard to call a periodic system because the scientist didn’t concentrate on similar qualities of elements. The main principles of his concept of atoms, described in his work A New System of Chemical Philosophy, were:
Despite the internal contradictions at the core of Dalton’s concept, some of its principles are still topical. For example, the atoms are not divided into parts, created or destroyed, but this is true only for chemical reactions. Dalton also did not know of the existence of isotopes of chemical elements, whose properties are sometimes different from the ”classic“ ones’ (Famous Scientists, n.d.).
Among the scientists who made a great contribution to the development of chemistry was a French chemist Antoine Lavoisier. His book, Elements of Chemistry, published in 1800s, is the first description of the modern chemistry science. The key achievements of this work were:
Jakob Berzelius was one of the most famous chemists of his time. In his scientific career, he has studied all the periods of chemistry development, from the creation of the oxygen theory by Lavoisier till the development of chemical atomism. The works of Berzelius were focused on the determination of atomic masses. He managed to identify the atomic masses of 45 chemical elements, and the results of his work were published in the form of the table in 1818. He did not use the term “molecule” and indicated what now is known as molecule as the atoms of varying complexity. To identify chemical elements, Berzelius suggested using the initial letters of their Latin names (1814) (Berzelius, Jöns Jacob, 2008). He also introduced the first formulae of chemical compounds (1817-30).
Berzelius gave a more precise definition to atomic masses. Moreover, he successfully applied the law of Gay-Lussac to determine the composition and quantitative characteristics of many elements and compounds. Berzelius realized the meaning of this law immediately after he read a work of the French scientist, relating to 1808. Even before Berzelius, Dalton used the atomic theory for new chemical symbols. Unlike Dalton, Berzelius adopted the atomic weight of oxygen, not hydrogen, as the basis for calculations. The atomic mass adopted by the Swedish scientist equals 100. From 1818 till 1826, Berzelius several times corrected the atomic masses (Berzelius, Jöns Jacob, 2008).
As a result of these studies, Berzelius significantly clarified the magnitude of atomic masses defined by Dalton. It created the preconditioned systematization of elements based on their atomic weights. These carefully performed researches allowed Berzelius make an atomic model of the basic chemistry.
Periodic table of chemical elements is a classification of the chemical elements, establishing the dependence of the properties of various elements regarding to the atomic nucleus. This system is a graphical representation of the periodic law, established by Russian chemist Mendeleev in 1869. In the modern version of the system, the elements are arranged in a two-dimensional table in which each column (group) defines the basic physical and chemical properties, and the lines are the periods, to a certain extent similar to each other (American Institute of Physics, n.d).
Mendeleev’s periodic system was an important milestone in the development of the atomic-molecular theory. After the creation of this table, the modern concept of chemical elements has been refined, as well as notions of simple substances and compounds. The periodic table was a systematization of types of atoms to new branches of physics, atomic and nuclear, which have developed in the early XX century (American Institute of Physics, n.d).
During the studies devoted to finding ways to apply the atom methods in physics, it has been found that the serial number of an element in the periodic table, also called a number of Mendeleev (atomic number) is a measure of the electric charge of the atomic core of this element. At the same time, the number of the horizontal row (period) in the table determines the number of electron shells of atoms, and the number of vertical row – the quantum structure of the upper shell.
The emergence of the periodic system and the discovery of the periodic law opened a new, truly scientific era in the history of chemistry and a number of related sciences: instead of the scattered facts about the elements and compounds, now there was a harmonious system, created by Mendeleev and his followers, which made it possible to analyze, generalize, and draw conclusions.
Henry Moseley is an English physicist, one of the founders of X-ray spectroscopy. According to Moseley, the charge number of the atomic nucleus (atomic number) is the number of protons in the atomic nucleus. The charge is equal to the number of nuclear charge in units of the elementary charge, and at the same time equal to the ordinal number of the corresponding nucleus of a chemical element in the periodic table. In 1913, he found the relationship between the frequency of the spectral lines of X-ray characteristics and the atomic number of the radiating element. This dependence has been named “ The law of Moseley”. This fundamental discovery was of great importance for establishing the physical meaning of the periodic table and the atomic number, as well as for validating the concept of planetary atom. Moseley’s discovery will always be one of the ten most brilliant in design, elegance and performance information content in the history of science (Ellis, 2013).
The periodic table has a great value to natural history and philosophy. The mentioned scientists did their best to help modern scientists of all spheres to consider chemical elements in their interrelation and forecast the characteristics of new elements.