The periodic table of elements is a table that contains all known chemical elements represented.
During the 19th century, chemists began to classify known chemical elements according to their physical and chemical properties. In 1860 the first International Congress of Chemists was organized in the German city of Karlsruhe with the aim of unifying the criteria for the classification of elements. This meeting was crucial in the history of science and the origin of the creation of the table that today appears in textbooks.
According to the International Union of Pure and Applied Chemistry (IUPAC) the periodic table of chemical elements was born on March 1, 1869.
How Many Chemical Elements Does the Periodic Table Contain?
Currently the periodic table contains 118 chemical elements.
The last elements that were introduced in the periodic table are elements 113, 115, 117 and 118. The names of these new elements are Nihonium, Moscovio, Teneso and Oganesón, respectively. This incorporation took place on December 1, 2016.
How Are the Chemical Elements Arranged on the Periodic Table?
The periodic table is organized in rows and columns. The columns are called groups, while the rows are known as periods.
The elements are arranged so that elements with similar electronic configurations are on top of each other. It is also ordered so that items with similar behaviors are in the same column.
What Is the Periodic Table For?
The periodic table has multiple uses in chemistry and other sciences. The most important ones are:
Show the relationships between the different chemical elements.
Predict the properties of elements that have just been discovered or that have not yet been synthesized.
Provides a useful picture when analyzing the chemical behaviors of chemicals.
What Is a Period on the Periodic Table?
A period in the periodic table corresponds to a horizontal row. Normally the clearest periodic trends are seen in the groups, however, there are certain regions of the table in which the trends in the horizontal direction are more prominent.
The elements of the same period in the table show trends in ionization potential, atomic radius, and electron affinity and electronegativity.
From left to right in a period, the atomic radius generally decreases. This is because in this direction each element in the table has an extra electron and proton, and the electrons approach the nucleus. This decrease in atomic radius ensures that over a period of time the ionization potential will also increase from left to right.
Electronegativity grows as does the ionization potential. This increase is due to the nucleus attracting electrons.
What Are the Groups or Families of the Periodic Table?
A group or family is a column in the periodic table of chemical elements. Typically, groups have more prominent periodic trends than blocks and periods.
Chemical elements that belong to the same group have similar chemical properties. In addition there is a clear tendency to increase in atomic numbers. But in some parts of the table the horizontal and vertical similarities can be just as important.
Properties of the Elements Within the Group
Elements in the same group tend to exhibit patterns of atomic radius, ionization potential, and electronegativity. From top to bottom, the atomic radius of the elements will increase per group, as there are more electrons and the valence electrons will be farther from the nucleus of the atom.
The electronegativity of families generally decreases as you move down the table. This decrease is due to the increase in the distance between the nucleus and the valence electrons.
What Are the Blocks of the Periodic Table?
The blocks are the specific regions of the periodic table of the elements. The block name corresponds to that of the shell that contains the last electron.
In the periodic table there are the following blocks:
The “s” block: includes the first and second groups that correspond to hydrogen, helium, alkali metals and alkaline earth metals.
Block "p" includes the last six groups. Among other elements, it includes noble gases and metalloids.
Block "d" includes groups between 3 and 12. This block contains all transition metals.
Block "f" has no group numbers. It is often represented below the rest of the table. The "f" block the actinides and lanthanides.
Who Is Credited with the Periodic Table?
The first recognizable periodic table was published by the Russian chemist Dmitri Mendeleev in 1869 in a work called "Principles of Chemistry." The way we organize chemical elements today still follows Mendeleev's proposal.
At the same time, the German chemist Julius Lothar Meyer, a contemporary competitor of Mendeleev, also worked with the idea of creating the first periodic table. Meyer ordered the elements based on the physical properties of atoms but his proposal was not so popular.
Since its inception, Mendeleev's periodic table of elements has been completed and expanded as other elements have been discovered or synthesized.
However, some scientists believe that the final version of the table was achieved thanks to the periodic law presented at the beginning of the 20th century by Henry Moseley.
Dmitri Mendeleev's Predictions
Mendeleev developed his table to show periodic trends in the 63 chemical elements that were known at the time. He also predicted some properties of chemicals that were unknown at the time but that he hoped would fill the gaps in the table.
When those new elements were discovered, his predictions turned out to be largely correct.